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‘All of the problems with evolutionary theory, as outlined in Genetic Entropy and the Mystery of the Genome, have now been rigorously proven using numerical simulation. We did this using “Mendel’s Accountant”, a state-of-the-art computer analytical tool for genetic systems. Five scientists—John Baumgardner, Wes Brewer, Paul Gibson, Walter ReMine, and I—developed this tool. We reported these new findings in two secular publications, and they will soon be discussed in a second book, Genetic Entropy and Mendel’s Accountant.’
The evolutionary biology of Hyrule laid out in a taxonomical chart for SUPER iam8bit 2011, an exhibition featuring over 100 artists exploring classic video games.
judebuffum.wordpress.com/2011/08/10/the-evolutionary-biol...
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Across the temporal universe this species has stood the evolutionary test of time.
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• Species Identification Group on Reddit
(A crowdsourced method of identifying unknown species of any organism through discussion with up or down votes and comments from tons of people including a bunch of biologists.)
• Artistic Photography Group on Reddit
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Wow, what an Epic, Joshua Tree National Park, California tour. Guided by the Evolutionary Futures Lab team
The latest on Instagram:
The program was part of the Nordic-Baltic Impact Week SOCAP program.
A business bridge for Sweden, the Nordic-Baltics and Silicon Valley.
Evolutionary Futures Lab:
The NBIW - SOCAP program is organised by CleanTech Region Impact Group. Accelerating Nordic-Baltic CleanTech solutions
Photo and video credit: Lars Ling
All rights reserved (c) copyright.
+++ DISCLAIMER +++
Nothing you see here is real, even though the conversion or the presented background story might be based on historical facts. BEWARE!
Some background:
The Hawker Furore was an evolutionary development of the successful Fury fighter. Like the Fury, the Furore was powered the liquid-cooled Rolls-Royce F.XI V-12 engine (later known as the Rolls-Royce Kestrel), which was also used by Hawker's new light bomber, the Hawker Hart.
The new fighter prototype first flew at Brooklands, Surrey, in March 1932, about a year after the Hawker Fury biplane had entered RAF service, and, in parallel, Hawker’s chief designer Sidney Camm also designed a monoplane version of the Fury, but it was held back since Rolls Royce was developing a new, more powerful engine at that time.
The Furore was a single-engine biplane and featured a modern all metal structure single bay wings and the Kestrel engine was enclosed by a smooth, streamlined cowling. But even though the new aircraft used many components from the Fury, it had a totally different look: The Furore had a novel configuration for a fighter, with the fuselage attached to the upper wing — somewhat like the 1914-designed German Gotha G.I bomber and the contemporary Handley Page Heyford heavy bomber. The lower wing was connected with to the fuselage through the landing gear struts, a pair of small pylons and by single struts between the outer wing sections. The fixed, spatted landing gear was integrated into the lower wing’s leading edge, and instead of the Fury’s tail skid the Furore was outfitted with a small wheel, which was spatted, too.
The rationale behind the unusual layout was the desire for a free field of view for the pilot, which was, in traditional designs, obscured by the upper wing. Another factor were improved aerodynamics through less struts, e.g. for the landing gear and between the wings, and attention was paid to reduce drag wherever possible. In the end, Furore and Fury had only their outlines in common, and maintenance of both types was very similar, but structurally the two types differed considerably from each other.
The armament was augmented to four 0.303 in (7.7 mm) machine guns: a synchronized pair fired through an innovative variable pitch three blade propeller (instead of the Fury’s wooden fixed-pitch two blade propeller), while two more of these weapons were integrated into the spat fairings, firing outside of the propeller arc.
Since Rolls Royce’s new engine was pending and in order to compare the Furore’s potential with the conservative Fury, the Air Ministry ordered at the start of 1933 a small initial production run for 21 aircraft. These machines, designated Furore Mk. I, were delivered in the course of early 1934 and distributed evenly among No. 25 and 43 squadron, which also operated the Hawker Fury as direct benchmark. One machine was kept at Hawker for further testing and development.
These trials soon showed that, despite the Furore’s slightly higher weight, the benefits from the aerodynamic cleaning effort outweighed this penalty. The improved firepower also spoke in favor of the Furore. However, the type’s handling was less appreciable, horizontal stability had suffered and the low ground clearance of the lower wing created an unexpected ground effect, which made landing the aircraft literally difficult. Furthermore, the unusual wing position resulted in an operational drawback: even though the pilot enjoyed an almost free, hemispherical field of view from the cockpit in flight, the view for- and downwards was hampered by the relative position of the upper wings and the cockpit, which made taxiing and especially landing – on top of the venturous ground effect – hazardous.
Despite these drawbacks, a second batch of 30 aircraft with some minor refinements (recognizable by longer spats) was ordered in late 1934 as Furore Mk. II, just a couple of weeks before Sidney Camm’s Fury monoplane design eventually came to official attention when Rolls-Royce presented their famous Merlin engine. The Fury monoplane’s design was then revised, according to Air Ministry specification F5/34, to become the prototype Hawker Hurricane. This highly successful type quickly replaced the RAF biplane fighters in frontline units from 1937 onwards, and from this point on, the small Furore fleet was quickly retired or used in liaison and meteorological duties 1940, when the type was retired.
General characteristics:
Crew: One
Length: 26 ft 11 in (8.20 m)
Wingspan: 30 ft 0 in (9.14 m)
Height: 12 ft 3 in (3.74 m)
Wing area: 250 ft² (23.2 m²)
Empty weight: 2,995 lb (1,360 kg)
Loaded weight: 3,800 lb (1,725 kg)
Powerplant:
1× Rolls-Royce Kestrel IV V12 engine, 680 hp (506 kW)
Performance:
Maximum speed: 245 mph at 16,500 ft (395 km/h at 5,030 m)
Range: 270 mi (435 km)
Service ceiling: 29,800 ft (9,100 m)
Rate of climb: 2,650 ft/min (13.5 m/s)
Wing loading: 14.4 lb/ft² (21.5 kg/m²)
Power/mass: 0.179 hp/lb (0.293 kW/kg)
Armament:
2× 0.303 in (7.7 mm) Vickers Mk IV machine guns with 500 RPG in the upper fuselage
2× 0.303 in Lewis machine guns with 350 PRG; one in each wheel fairing
The kit and its assembly:
This one is another contribution to the “RAF Centenary” Group Build at whatifmodelers.com. It was actually inspired by a Matchbox Handley Page Heyford in my stash – I looked at the box an asked myself “Why did you buy this…?”. However, the Heyford and its unique layout made me wonder how a contemporary fighter might have looked like? Looking for a potential conversion basis I stumbled upon the Hawker Fury biplane – its structure looked like a good basis.
Said and done, I organized a Matchbox Fury in the form of a Revell re-boxing. I was shocked to see, though, that this re-issue is of really poor quality, with lots of flash and even some sinkholes! I have no idea what Revell did to the originally very crisp Matchbox molds!?
Conversion work started with wing surgery: the upper wing lost a middle section, which was transplanted between the lower wings, which were cut off from their fuselage connector. The latter was used as a plug to fill the ventral gap between the lower wings’ original position.
Cockpit and tail were taken OOB (I just used a single pair of stabilizing struts instead of two), but I added a spine fairing behind the cockpit (a leftover piece from an Airfix P-61 drop tank) and mounted a taller windscreen.
The upper wings were then mounted directly to the fuselage, under the machine gun mounts. The radiator was placed into its original, ventral position. The lower wing then received a pair of spatted wheels (Eduard resin replacements for an Avia B.534), since I wanted to integrate them into the hull and reduce the overall number of struts. In a wake of more modernization, I also added a pair of machine gun gondolas (from a Gloster Gladiator) on top of them, and the spats were elongated and blended into the wings with 2C putty.
Mounting the lower wing freely under the fuselage was the biggest stunt – I eventually settled on using the Fury’s landing gear struts as connectors – they’d also ensure a proper height of the aircraft. Once they were in place, I added another pair of struts between the fuselage and the lower wing, for a proper angle of attack. After letting this wobbly affair dry thoroughly, the wings were connected with four tailor-made single struts, created from the OOB N-shaped struts. The result is quite stable!
The original wooden, two-blade propeller was replaced by a more modern three-blade propeller with a round spinner; it comes from an Airfix Westland Whirlwind, but had to be modified in order to fit onto the Fury’s nose. Internally, a styrene tube and a metal axis were added.
After the good experience with my recent TR.2 build, the rigging was done as a final step after painting and applying varnish – as per usual, I used dark grey styrene material and white glue.
Painting and markings:
Not many choices here – either a colorful aircraft in overall silver, or a toned-down, camouflaged livery. I settled for the latter, in a typical 1938-39 livery in Dark Green and Dark Earth (Tamiya XF-61 and Humbrol 29). The fuselage and stabilizer undersurfaces were painted in aluminum (Revell 99), while the outer wings became black (Revell 09) and white (Humbrol 22, with a little 147 added).
The cockpit interior was painted in Tar Black (Revell 06), while the spinner became black and Dark Earth. The propeller blades received bare metal front sides, while the rear became black, with yellow tips.
After a black ink wash the model received a post-shading treatment. The decals were puzzled together from the scrap box, e.g. with roundels from an Italeri Tornado, medium sea grey code letters from Xtradecal and serials and some other markings from an Airfix Hurricane. The yellow trim as flight marking on the spats is the only extraordinary addition to the otherwise sombre look.
After some light soot stains around the exhausts, the kit was sealed with matt acrylic varnish from the rattle can. The final step was the rigging, which I tried to keep at a plausible minimum.
A thorough conversion, even though almost the complete original Fury kit could be used! And the result is really ambiguous – on one side, the resulting Furore looks both plausible and very Thirties, like one of those many weird designs that were spawned during the transitional era between biplanes and monoplanes. The build was intended to look like the missing link between the Fury and the Hurricane, and I think that I achieved that. On the other side, the “Heyford effect” takes full effect: despite being based on a sleek and elegant aircraft, and with no major additions, the “re-arranged” Furore looks quite bulky and very massive.
Rapid strata formation in soft sand (field evidence).
Photo of strata formation in soft sand on a beach, created by tidal action of the sea.
Formed in a single, high tidal event. Stunning evidence which displays multiple strata/layers.
Why this is so important ....
It has long been assumed, ever since the 17th century, that layers/strata observed in sedimentary rocks were built up gradually, layer upon layer, over many years. It certainly seemed logical at the time, from just looking at rocks, that lower layers would always be older than the layers above them, i.e. that lower layers were always laid down first followed, in time, by successive layers on top.
This was assumed to be true and became known as the superposition principle.
It was also assumed that a layer comprising a different material from a previous layer, represented a change in environmental conditions/factors.
These changes in composition of layers or strata were considered to represent different, geological eras on a global scale, spanning millions of years. This formed the basis for the Geologic Column, which is used to date rocks and also fossils. The evolutionary, 'fossil record' was based on the vast ages and assumed geological eras of the Geologic Column.
There was also circular reasoning applied with the assumed age of 'index' fossils (based on evolutionary beliefs & preconceptions) used to date strata in the Geologic Column. Dating strata from the assumed age of fossils is known as Biostratigraphy.
We now know that, although these assumptions seemed logical, they are not supported by the evidence.
At the time, the mechanics of stratification were not properly known or studied.
An additional factor was that this assumed superposition and uniformitarian model became essential, with the wide acceptance of Darwinism, for the long ages required for progressive microbes-to-human evolution. There was no incentive to question or challenge the superposition, uniformitarian model, because the presumed, fossil 'record' had become dependant on it, and any change in the accepted model would present devastating implications for Darwinism.
This had the unfortunate effect of linking the study of geology so closely to Darwinism, that any study independent of Darwinian considerations was effectively stymied.
Some of the wealth of evidence can be observed here: field evidence www.flickr.com/photos/101536517@N06/sets/72157635944904973/
and also in the links to stunning, experimental evidence, carried out by sedimentologists, given later..
_______________________________________________
GEOLOGIC PRINCIPLES (established by Nicholas Steno in the 17th Century):
What Nicolas Steno believed about strata formation is the basis of the principle of Superposition and the principle of Original Horizontality.
dictionary.sensagent.com/Law_of_superposition/en-en/
“Assuming that all rocks and minerals had once been fluid, Nicolas Steno reasoned that rock strata were formed when particles in a fluid such as water fell to the bottom. This process would leave horizontal layers. Thus Steno's principle of original horizontality states that rock layers form in the horizontal position, and any deviations from this horizontal position are due to the rocks being disturbed later.”)
BEDDING PLANES.
'Bedding plane' describes the surface in between each stratum which are formed during sediment deposition.
science.jrank.org/pages/6533/Strata.html
“Strata form during sediment deposition, that is, the laying down of sediment. Meanwhile, if a change in current speed or sediment grain size occurs or perhaps the sediment supply is cut off, a bedding plane forms. Bedding planes are surfaces that separate one stratum from another. Bedding planes can also form when the upper part of a sediment layer is eroded away before the next episode of deposition. Strata separated by a bedding plane may have different grain sizes, grain compositions, or colours. Sometimes these other traits are better indicators of stratification as bedding planes may be very subtle.”
______________________________________________
Several catastrophic events, flash floods, volcanic eruptions etc. have forced Darwinian, influenced geologists to admit to rapid stratification in some instances. However they claim it is a rare phenomenon, which they have known about for many years, and which does nothing to invalidate the Geologic Column, the fossil record, evotuionary timescale, or any of the old assumptions regarding strata formation, sedimentation and the superposition principle. They fail to face up to the fact that rapid stratification is not an extraordinary phenonemon, but rather the prevailing and normal mechanism of sedimentary deposition whenever and wherever there is moving, sediment-laden water. The experimental evidence demonstrates the mechanism and a mass of field evidence in normal (non-catastrophic) conditions shows it is a normal everyday occurrence.
It is clear from the experimental evidence that the usual process of stratification is - that strata are not formed by horizontal layers being laid on top of each other in succession, as was assumed. But by sediment being sorted in the flowing water and laid down diagonally in the direction of flow. See diagram:
www.flickr.com/photos/truth-in-science/39821536092/in/dat...
The field evidence (in the image) presented here - of rapid, simultaneous stratification refutes the Superposition Principle, and the Principle of Lateral Continuity.
We now know, the Superposition Principle only applies on a rare occasion of sedimentary deposits in perfectly, still water. Superposition is required for the long evolutionary timescale, but the evidence shows it is not the general rule, as was once believed. Most sediment is laid down in moving water, where particle segregation is the general rule, resulting in the simultaneous deposition of strata/layers as shown in the photo.
See many other examples of rapid stratification with geological features: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Rapid, simultaneous formation of layers/strata, through particle segregation in moving water, is so easily created it has even been described by sedimentologists (working on flume experiments) as a law ...
"Upon filling the tank with water and pouring in sediments, we immediately saw what was to become the rule: The sediments sorted themselves out in very clear layers. This became so common that by the end of two weeks, we jokingly referred to Andrew's law as "It's difficult not to make layers," and Clark's law as "It's easy to make layers." Later on, I proposed the "law" that liquefaction destroys layers, as much to my surprise as that was." Ian Juby, www.ianjuby.org/sedimentation/
The example in the photo is the result of normal, everyday tidal action in a single incident. Where the water current or movement is more turbulent, violent, or catastrophic, great depths (many metres) of stratified sediment can be laid down in a short time. Certainly not the many millions of years assumed by evolutionists.
The composition of strata formed in any deposition event. is related to whatever materials are in the sediment mix, not to any particular timescale. Whatever is in the mix will be automatically sorted into strata/layers. It could be sand, or other material added from mud slides, erosion of chalk deposits, coastal erosion, volcanic ash etc. Any organic material (potential fossils), alive or dead, engulfed by, or swept into, a turbulent sediment mix, will also be sorted and buried within the rapidly, forming layers.
See many other examples of rapid stratification with geological features: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Stratified, soft sand deposit. demonstrates the rapid, stratification principle.
Important, field evidence which supports the work of the eminent, sedimentologist Dr Guy Berthault MIAS - Member of the International Association of Sedimentologists.
(Dr Berthault's experiments (www.sedimentology.fr/)
And also the experimental work of Dr M.E. Clark (Professor Emeritus, U of Illinois @ Urbana), Andrew Rodenbeck and Dr. Henry Voss, (www.ianjuby.org/sedimentation/)
Location: Sandown, Isle of Wight. Formed 21/02/2018, This field evidence demonstrates that multiple strata in sedimentary deposits do not need millions of years to form and can be formed rapidly. This natural example confirms the principle demonstrated by the sedimentation experiments carried out by Dr Guy Berthault and other sedimentologists. It calls into question the standard, multi-million year dating of sedimentary rocks, and the dating of fossils by depth of burial or position in the strata.
Mulltiple strata/layers are evident in this example.
Dr Berthault's experiments (www.sedimentology.fr/) and other experiments (www.ianjuby.org/sedimentation/) and field studies of floods and volcanic action show that, rather than being formed by gradual, slow deposition of sucessive layers superimposed upon previous layers, with the strata or layers representing a particular timescale, particle segregation in moving water or airborne particles can form strata or layers very quickly, frequently, in a single event.
And, most importantly, lower strata are not necessarily older than upper strata, they can be the same age, having been created in the same, sedimentary episode.
Such field studies confirm experiments which have shown that there is no longer any reason to conclude that strata/layers in sedimentary rocks relate to different geological eras and/or a multi-million year timescale. www.youtube.com/watch?v=5PVnBaqqQw8&feature=share&.... they also show that the relative position of fossils in rocks is not indicative of an order of evolutionary succession. Obviously, the uniformitarian principle, on which the geologic column is based, can no longer be considered valid. And the multi-million, year dating of sedimentary rocks and fossils needs to be reassessed. Rapid deposition of stratified sediments also explains the enigma of polystrate fossils, i.e. large fossils that intersect several strata. In some cases, tree trunk fossils are found which intersect the strata of sedimentary rock up to forty feet in depth. upload.wikimedia.org/wikipedia/commons/thumb/0/08/Lycopsi... They must have been buried in stratified sediment in a short time (certainly not millions, thousands, or even hundreds of years), or they would have rotted away. youtu.be/vnzHU9VsliQ
In fact, the vast majority of fossils are found in good, intact condition, which is testament to their rapid burial. You don't get good fossils from gradual burial, because they would be damaged or destroyed by decay, predation or erosion. The existence of so many fossils in sedimentary rock on a global scale is stunning evidence for the rapid depostion of sedimentary rock as the general rule. It is obvious that all rock containing good intact fossils was formed from sediment laid down in a very short time, not millions, or even thousands of years.
See set of photos of other examples of rapid stratification: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Carbon dating of coal should not be possible if it is millions of years old, yet significant amounts of Carbon 14 have been detected in coal and other fossil material, which indicates that it is less than 50,000 years old. www.ldolphin.org/sewell/c14dating.html
www.grisda.org/origins/51006.htm
Evolutionists confidently cite multi-million year ages for rocks and fossils, but what most people don't realise is that no one actually knows the age of sedimentary rocks or the fossils found within them. So how are evolutionists so sure of the ages they so confidently quote? The astonishing thing is they aren't. Sedimentary rocks cannot be dated by radiometric methods*, and fossils can only be dated to less than 50,000 years with Carbon 14 dating. The method evolutionists use is based entirely on assumptions. Unbelievably, fossils are dated by the assumed age of rocks, and rocks are dated by the assumed age of fossils, that's right ... it is known as circular reasoning.
* Regarding the radiometric dating of igneous rocks, which is claimed to be relevant to the dating of sedimentary rocks, in an occasional instance there is an igneous intrusion associated with a sedimentary deposit -
Prof. Aubouin says in his Précis de Géologie: "Each radioactive element disintegrates in a characteristic and constant manner, which depends neither on the physical state (no variation with pressure or temperature or any other external constraint) nor on the chemical state (identical for an oxide or a phosphate)."
"Rocks form when magma crystallizes. Crystallisation depends on pressure and temperature, from which radioactivity is independent. So, there is no relationship between radioactivity and crystallisation.
Consequently, radioactivity doesn't date the formation of rocks. Moreover, daughter elements contained in rocks result mainly from radioactivity in magma where gravity separates the heavier parent element, from the lighter daughter element. Thus radiometric dating has no chronological signification." Dr. Guy Berthault www.sciencevsevolution.org/Berthault.htm
Visit the fossil museum:
www.flickr.com/photos/101536517@N06/sets/72157641367196613/
Just how good are peer reviews of scientific papers?
www.sciencemag.org/content/342/6154/60.full
www.examiner.com/article/want-to-publish-science-paper-ju...
The neo-Darwinian idea that the human genome consists entirely of an accumulation of billions of mutations is, quite obviously, completely bonkers. Nevertheless, it is compulsorily taught in schools and universities as 'science'.
The reason for this encephalization is difficult to discern, as the major changes from Homo erectus to Homo heidelbergensis were not associated with major changes in technology. It has been suggested that the changes have been associated with social changes, increased empathic abilities and increases in size of social groupings.Human evolution is the evolutionary process that led to the emergence of anatomically modern humans, beginning with the evolutionary history of primates.The increase in volume over time has affected areas within the brain unequally—the temporal lobes, which contain centers for language processing, have increased disproportionately, and seems to favor a belief that there was evolution after leaving Africa, as has the prefrontal cortex which has been related to complex decision-making and moderating social behavior.Encephalization has been tied to an increasing emphasis on meat in the diet, or with the development of cooking, and it has been proposed that intelligence increased as a response to an increased necessity for solving social problems as human society became more complex. The human brain was able to expand because of the changes in the morphology of smaller mandibles and mandible muscle attachments to the skull into allowing more room for the brain to grow – in particular genus Homo – and leading to the emergence of Homo sapiens as a distinct species of the hominid family, the great apes.The human species eventually developed a much larger brain than that of other primates—typically 1,330 cm3 in modern humans, nearly three times the size of that of a chimpanzee or gorilla. The pattern of encephalization started with Homo habilis, after a hiatus with Anamensis and Ardipithecus species which had smaller brains as a result of their bipedal locomotion which at approximately 600 cm3 Homo habilus had a brain slightly larger than that of chimpanzees, and this evolution continued with Homo erectus (800–1,100 cm3), reaching a maximum in Neanderthals with an average size of (1,200–1,900 cm3), larger even than modern Homo sapiens. This pattern of brain increase happened through the pattern of human postnatal brain growth which differs from that of other apes (heterochrony). It also allows for extended periods of social learning and language acquisition in juvenile humans which may have begun 2 million years ago. However, the differences between the structure of human brains and those of other apes may be even more significant than differences in size. The study of human evolution involves many scientific disciplines, including physical anthropology, primatology, archaeology, paleontology, neurobiology, ethology, linguistics, evolutionary psychology, embryology and genetics.[1] Genetic studies show that primates diverged from other mammals about 85 million years ago, in the Late Cretaceous period, and the earliest fossils appear in the Paleocene, around 55 million years ago.Within the Hominoidea (apes) superfamily, the Hominidae family diverged from the Hylobatidae (gibbon) family some 15–20 million years ago; African great apes (subfamily Homininae) diverged from orangutans (Ponginae) about 14 million years ago; the Hominini tribe (humans, Australopithecines and other extinct biped genera, and chimpanzees) parted from the Gorillini tribe (gorillas) between 9 million years ago and 8 million years ago; and, in turn, the subtribes Hominina (humans and biped ancestors) and Panina (chimps) separated about 7.5 million years ago to 5.6 million years ago.Human evolution from its first separation from the last common ancestor of humans and chimpanzees is characterized by a number of morphological, developmental, physiological, and behavioral changes. The most significant of these adaptations are bipedalism, increased brain size, lengthened ontogeny (gestation and infancy), and decreased sexual dimorphism. The relationship between these changes is the subject of ongoing debate. Other significant morphological changes included the evolution of a power and precision grip, a change first occurring in H. erectus.Bipedalism is the basic adaptation of the hominin and is considered the main cause behind a suite of skeletal changes shared by all bipedal hominins. The earliest hominin, of presumably primitive bipedalism, is considered to be either Sahelanthropus[6] or Orrorin, both of which arose some 6 to 7 million years ago. The non-bipedal knuckle-walkers, the gorilla and chimpanzee, diverged from the hominin line over a period covering the same time, so either of Sahelanthropus or Orrorin may be our last shared ancestor. Ardipithecus, a full biped, arose somewhat later.The early bipeds eventually evolved into the australopithecines and still later into the genus Homo. There are several theories of the adaptation value of bipedalism. It is possible that bipedalism was favored because it freed the hands for reaching and carrying food, saved energy during locomotion,enabled long distance running and hunting, provided an enhanced field of vision, and helped avoid hyperthermia by reducing the surface area exposed to direct sun; features all advantageous for thriving in the new savanna and woodland environment created as a result of the East African Rift Valley uplift versus the previous closed forest habitat. A new study provides support for the hypothesis that walking on two legs, or bipedalism, evolved because it used less energy than quadrupedal knuckle-walking.However, recent studies suggest that bipedality without the ability to use fire would not have allowed global dispersal.This change in gait saw a lengthening of the legs proportionately when compared to the length of the arms, which were shortened through the removal of the need for brachiation. Another change is the shape of the big toe. Recent studies suggest that Australopithecines still lived part of the time in trees as a result of maintaining a grasping big toe. This was progressively lost in Habilines.Anatomically, the evolution of bipedalism has been accompanied by a large number of skeletal changes, not just to the legs and pelvis, but also to the vertebral column, feet and ankles, and skull.The femur evolved into a slightly more angular position to move the center of gravity toward the geometric center of the body. The knee and ankle joints became increasingly robust to better support increased weight. To support the increased weight on each vertebra in the upright position, the human vertebral column became S-shaped and the lumbar vertebrae became shorter and wider. In the feet the big toe moved into alignment with the other toes to help in forward locomotion. The arms and forearms shortened relative to the legs making it easier to run. The foramen magnum migrated under the skull and more anterior.The most significant changes occurred in the pelvic region, where the long downward facing iliac blade was shortened and widened as a requirement for keeping the center of gravity stable while walking;[15] bipedal hominids have a shorter but broader, bowl-like pelvis due to this. A drawback is that the birth canal of bipedal apes is smaller than in knuckle-walking apes, though there has been a widening of it in comparison to that of australopithecine and modern humans, permitting the passage of newborns due to the increase in cranial size but this is limited to the upper portion, since further increase can hinder normal bipedal movement.The shortening of the pelvis and smaller birth canal evolved as a requirement for bipedalism and had significant effects on the process of human birth which is much more difficult in modern humans than in other primates. During human birth, because of the variation in size of the pelvic region, the fetal head must be in a transverse position (compared to the mother) during entry into the birth canal and rotate about 90 degrees upon exit.The smaller birth canal became a limiting factor to brain size increases in early humans and prompted a shorter gestation period leading to the relative immaturity of human offspring, who are unable to walk much before 12 months and have greater neoteny, compared to other primates, who are mobile at a much earlier age.The increased brain growth after birth and the increased dependency of children on mothers had a big effect upon the female reproductive cycle,[and the more frequent appearance of alloparenting in humans when compared with other hominids.Delayed human sexual maturity also led to the evolution of menopause with one explanation providing that elderly women could better pass on their genes by taking care of their daughter's offspring, as compared to having more children of their own.The genetic revolution in studies of human evolution started when Vincent Sarich and Allan Wilson measured the strength of immunological cross-reactions of blood serum albumin between pairs of creatures, including humans and African apes (chimpanzees and gorillas).The strength of the reaction could be expressed numerically as an immunological distance, which was in turn proportional to the number of amino acid differences between homologous proteins in different species. By constructing a calibration curve of the ID of species' pairs with known divergence times in the fossil record, the data could be used as a molecular clock to estimate the times of divergence of pairs with poorer or unknown fossil records.In their seminal 1967 paper in Science, Sarich and Wilson estimated the divergence time of humans and apes as four to five million years ago,[54] at a time when standard interpretations of the fossil record gave this divergence as at least 10 to as much as 30 million years. Subsequent fossil discoveries, notably "Lucy", and reinterpretation of older fossil materials, notably Ramapithecus, showed the younger estimates to be correct and validated the albumin method.Progress in DNA sequencing, specifically mitochondrial DNA (mtDNA) and then Y-chromosome DNA (Y-DNA) advanced the understanding of human origins.[55][8][56] Application of the molecular clock principle revolutionized the study of molecular evolution.On the basis of a separation from the orangutan between 10 and 20 million years ago, earlier studies of the molecular clock suggested that there were about 76 mutations per generation that were not inherited by human children from their parents; this evidence supported the divergence time between hominins and chimps noted above. However, a 2012 study in Iceland of 78 children and their parents suggests a mutation rate of only 36 mutations per generation; this datum extends the separation between humans and chimps to an earlier period greater than 7 million years ago (Ma). Additional research with 226 offspring of wild chimp populations in 8 locations suggests that chimps reproduce at age 26.5 years, on average; which suggests the human divergence from chimps occurred between 7 and 13 million years ago. And these data suggest that Ardipithecus (4.5 Ma), Orrorin (6 Ma) and Sahelanthropus (7 Ma) all may be on the hominid lineage, and even that the separation may have occurred outside the East African Rift region.Furthermore, analysis of the two species' genes in 2006 provides evidence that after human ancestors had started to diverge from chimpanzees, interspecies mating between "proto-human" and "proto-chimps" nonetheless occurred regularly enough to change certain genes in the new gene pool:A new comparison of the human and chimp genomes suggests that after the two lineages separated, they may have begun interbreeding... A principal finding is that the X chromosomes of humans and chimps appear to have diverged about 1.2 million years more recently than the other chromosomes.The research suggests:There were in fact two splits between the human and chimp lineages, with the first being followed by interbreeding between the two populations and then a second split. The suggestion of a hybridization has startled paleoanthropologists, who nonetheless are treating the new genetic data seriously.
H. floresiensis, which lived from approximately 190,000 to 50,000 years before present, has been nicknamed hobbit for its small size, possibly a result of insular dwarfism.[160] H. floresiensis is intriguing both for its size and its age, being an example of a recent species of the genus Homo that exhibits derived traits not shared with modern humans. In other words, H. floresiensis shares a common ancestor with modern humans, but split from the modern human lineage and followed a distinct evolutionary path. The main find was a skeleton believed to be a woman of about 30 years of age. Found in 2003, it has been dated to approximately 18,000 years old. The living woman was estimated to be one meter in height, with a brain volume of just 380 cm3 (considered small for a chimpanzee and less than a third of the H. sapiens average of 1400 cm3).[citation needed]
However, there is an ongoing debate over whether H. floresiensis is indeed a separate species.[161] Some scientists hold that H. floresiensis was a modern H. sapiens with pathological dwarfism.[162] This hypothesis is supported in part, because some modern humans who live on Flores, the Indonesian island where the skeleton was found, are pygmies. This, coupled with pathological dwarfism, could have resulted in a significantly diminutive human. The other major attack on H. floresiensis as a separate species is that it was found with tools only associated with H. sapiens.
Homo floresiensis
The hypothesis of pathological dwarfism, however, fails to explain additional anatomical features that are unlike those of modern humans (diseased or not) but much like those of ancient members of our genus. Aside from cranial features, these features include the form of bones in the wrist, forearm, shoulder, knees, and feet. Additionally, this hypothesis fails to explain the find of multiple examples of individuals with these same characteristics, indicating they were common to a large population, and not limited to one individual
Rapid strata formation in soft sand (field evidence).
Photo of strata formation in soft sand, with geological features, on a beach, created by tidal action of the sea.
Formed in a single, high tidal event. Stunning evidence which displays multiple strata/layers.
Why this is so important ....
It has long been assumed, ever since the 17th century, that layers/strata observed in sedimentary rocks were built up gradually, layer upon layer, over many years. It certainly seemed logical at the time, from just looking at rocks, that lower layers would always be older than the layers above them, i.e. that lower layers were always laid down first followed, in time, by successive layers on top.
This was assumed to be true and became known as the superposition principle.
It was also assumed that a layer comprising a different material from a previous layer, represented a change in environmental conditions/factors.
These changes in composition of layers or strata were considered to represent different, geological eras on a global scale, spanning millions of years. This formed the basis for the Geologic Column, which is used to date rocks and also fossils. The evolutionary, 'fossil record' was based on the vast ages and assumed geological eras of the Geologic Column.
There was also circular reasoning applied with the assumed age of 'index' fossils (based on evolutionary preconceptions) used to date strata in the Geologic Column.
We now know that, although these assumptions seemed logical, they are not supported by the evidence.
At the time, the mechanics of stratification were not properly known or studied.
An additional factor was that this assumed superposition and uniformitarian model became essential, with the wide acceptance of Darwinism, for the long ages required for progressive microbes-to-human evolution. There was no incentive to question or challenge the superposition, uniformitarian model, because the presumed, fossil 'record' had become dependant on it, and any change in the accepted model would present devastating implications for Darwinism.
This had the unfortunate effect of linking the study of geology so closely to Darwinism, that any study independent of Darwinian considerations was effectively stymied. This link of geology with Darwinian preconceptions is known as biostratigraphy.
Some of the wealth of evidence can be observed here: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
and also in the links to stunning, experimental evidence, carried out by sedimentologists, given later.
_______________________________________________
GEOLOGIC PRINCIPLES (established by Nicholas Steno in the 17th Century):
What Nicolas Steno believed about strata formation is the basis of the principle of Superposition and the principle of Original Horizontality.
dictionary.sensagent.com/Law_of_superposition/en-en/
“Assuming that all rocks and minerals had once been fluid, Nicolas Steno reasoned that rock strata were formed when particles in a fluid such as water fell to the bottom. This process would leave horizontal layers. Thus Steno's principle of original horizontality states that rock layers form in the horizontal position, and any deviations from this horizontal position are due to the rocks being disturbed later.”)
BEDDING PLANES.
'Bedding plane' describes the surface in between each stratum which are formed during sediment deposition.
science.jrank.org/pages/6533/Strata.html
“Strata form during sediment deposition, that is, the laying down of sediment. Meanwhile, if a change in current speed or sediment grain size occurs or perhaps the sediment supply is cut off, a bedding plane forms. Bedding planes are surfaces that separate one stratum from another. Bedding planes can also form when the upper part of a sediment layer is eroded away before the next episode of deposition. Strata separated by a bedding plane may have different grain sizes, grain compositions, or colours. Sometimes these other traits are better indicators of stratification as bedding planes may be very subtle.”
______________________________________________
Several catastrophic events, flash floods, volcanic eruptions etc. have forced Darwinian, influenced geologists to admit to rapid stratification in some instances. However they claim it is a rare phenomenon, which they have known about for many years, and which does nothing to invalidate the Geologic Column, the fossil record, evotuionary timescale, or any of the old assumptions regarding strata formation, sedimentation and the superposition principle. They fail to face up to the fact that rapid stratification is not an extraordinary phenonemon, but rather the prevailing and normal mechanism of sedimentary deposition whenever and wherever there is moving, sediment-laden water. The experimental evidence demonstrates the mechanism and a mass of field evidence in normal (non-catastrophic) conditions shows it is a normal everyday occurrence.
It is clear from the experimental evidence that the usual process of stratification is - that strata are not formed by horizontal layers being laid on top of each other in succession, as was assumed. But by sediment being sorted in the flowing water and laid down diagonally in the direction of flow. See diagram:
www.flickr.com/photos/truth-in-science/39821536092/in/dat...
The field evidence (in the image) presented here - of rapid, simultaneous stratification refutes the Superposition Principle, the Principle of Original Horizontality and the Principle of Lateral Continuity.
We now know, the Superposition Principle only applies on a rare occasion of sedimentary deposits in perfectly, still water. Superposition is required for the long evolutionary timescale, but the evidence shows it is not the general rule, as was once believed. Most sediment is laid down in moving water, where particle segregation is the general rule, resulting in the simultaneous deposition of strata/layers as shown in the photo.
See many other examples of rapid stratification with geological features: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Rapid, simultaneous formation of layers/strata, through particle segregation in moving water, is so easily created it has even been described by sedimentologists (working on flume experiments) as a law ...
"Upon filling the tank with water and pouring in sediments, we immediately saw what was to become the rule: The sediments sorted themselves out in very clear layers. This became so common that by the end of two weeks, we jokingly referred to Andrew's law as "It's difficult not to make layers," and Clark's law as "It's easy to make layers." Later on, I proposed the "law" that liquefaction destroys layers, as much to my surprise as that was." Ian Juby, www.ianjuby.org/sedimentation/
The example in the photo is the result of normal, everyday tidal action in a single incident. Where the water current or movement is more turbulent, violent, or catastrophic, great depths (many metres) of stratified sediment can be laid down in a short time. Certainly not the many millions of years assumed by evolutionists.
The composition of strata formed in any deposition event. is related to whatever materials are in the sediment mix, not to any particular timescale. Whatever is in the mix will be automatically sorted into strata/layers. It could be sand, or other material added from mud slides, erosion of chalk deposits, coastal erosion, volcanic ash etc. Any organic material (potential fossils), alive or dead, engulfed by, or swept into, a turbulent sediment mix, will also be sorted and buried within the rapidly, forming layers.
See many other examples of rapid stratification with geological features: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Stratified, soft sand deposit. demonstrates the rapid, stratification principle.
Important, field evidence which supports the work of the eminent, sedimentologist Dr Guy Berthault MIAS - Member of the International Association of Sedimentologists.
(Dr Berthault's experiments (www.sedimentology.fr/)
And also the experimental work of Dr M.E. Clark (Professor Emeritus, U of Illinois @ Urbana), Andrew Rodenbeck and Dr. Henry Voss, (www.ianjuby.org/sedimentation/)
Location: Sandown, Isle of Wight. Formed 17/01/2018, This field evidence demonstrates that multiple strata in sedimentary deposits do not need millions of years to form and can be formed rapidly. This natural example confirms the principle demonstrated by the sedimentation experiments carried out by Dr Guy Berthault and other sedimentologists. It calls into question the standard, multi-million year dating of sedimentary rocks, and the dating of fossils by depth of burial or position in the strata.
Mulltiple strata/layers are evident in this example.
Dr Berthault's experiments (www.sedimentology.fr/) and other experiments (www.ianjuby.org/sedimentation/) and field studies of floods and volcanic action show that, rather than being formed by gradual, slow deposition of sucessive layers superimposed upon previous layers, with the strata or layers representing a particular timescale, particle segregation in moving water or airborne particles can form strata or layers very quickly, frequently, in a single event.
And, most importantly, lower strata are not older than upper strata, they are the same age, having been created in the same sedimentary episode.
Such field studies confirm experiments which have shown that there is no longer any reason to conclude that strata/layers in sedimentary rocks relate to different geological eras and/or a multi-million year timescale. www.youtube.com/watch?v=5PVnBaqqQw8&feature=share&.... they also show that the relative position of fossils in rocks is not indicative of an order of evolutionary succession. Obviously, the uniformitarian principle, on which the geologic column is based, can no longer be considered valid. And the multi-million, year dating of sedimentary rocks and fossils needs to be reassessed. Rapid deposition of stratified sediments also explains the enigma of polystrate fossils, i.e. large fossils that intersect several strata. In some cases, tree trunk fossils are found which intersect the strata of sedimentary rock up to forty feet in depth. upload.wikimedia.org/wikipedia/commons/thumb/0/08/Lycopsi... They must have been buried in stratified sediment in a short time (certainly not millions, thousands, or even hundreds of years), or they would have rotted away. youtu.be/vnzHU9VsliQ
In fact, the vast majority of fossils are found in good, intact condition, which is testament to their rapid burial. You don't get good fossils from gradual burial, because they would be damaged or destroyed by decay, predation or erosion. The existence of so many fossils in sedimentary rock on a global scale is stunning evidence for the rapid depostion of sedimentary rock as the general rule. It is obvious that all rock containing good intact fossils was formed from sediment laid down in a very short time, not millions, or even thousands of years.
See set of photos of other examples of rapid stratification: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Carbon dating of coal should not be possible if it is millions of years old, yet significant amounts of Carbon 14 have been detected in coal and other fossil material, which indicates that it is less than 50,000 years old. www.ldolphin.org/sewell/c14dating.html
www.grisda.org/origins/51006.htm
Evolutionists confidently cite multi-million year ages for rocks and fossils, but what most people don't realise is that no one actually knows the age of sedimentary rocks or the fossils found within them. So how are evolutionists so sure of the ages they so confidently quote? The astonishing thing is they aren't. Sedimentary rocks cannot be dated by radiometric methods*, and fossils can only be dated to less than 50,000 years with Carbon 14 dating. The method evolutionists use is based entirely on assumptions. Unbelievably, fossils are dated by the assumed age of rocks, and rocks are dated by the assumed age of fossils, that's right ... it is known as circular reasoning.
* Regarding the radiometric dating of igneous rocks, which is claimed to be relevant to the dating of sedimentary rocks, in an occasional instance there is an igneous intrusion associated with a sedimentary deposit -
Prof. Aubouin says in his Précis de Géologie: "Each radioactive element disintegrates in a characteristic and constant manner, which depends neither on the physical state (no variation with pressure or temperature or any other external constraint) nor on the chemical state (identical for an oxide or a phosphate)."
"Rocks form when magma crystallizes. Crystallisation depends on pressure and temperature, from which radioactivity is independent. So, there is no relationship between radioactivity and crystallisation.
Consequently, radioactivity doesn't date the formation of rocks. Moreover, daughter elements contained in rocks result mainly from radioactivity in magma where gravity separates the heavier parent element, from the lighter daughter element. Thus radiometric dating has no chronological signification." Dr. Guy Berthault www.sciencevsevolution.org/Berthault.htm
Visit the fossil museum:
www.flickr.com/photos/101536517@N06/sets/72157641367196613/
Just how good are peer reviews of scientific papers?
www.sciencemag.org/content/342/6154/60.full
www.examiner.com/article/want-to-publish-science-paper-ju...
The neo-Darwinian idea that the human genome consists entirely of an accumulation of billions of mutations is, quite obviously, completely bonkers. Nevertheless, it is compulsorily taught in schools and universities as 'science'.
Cape Baboons in the Upper Thendele Camp
Bärenpaviane im Upper Thendele Camp
(Wikipedia)
The chacma baboon (Papio ursinus), also known as the Cape baboon, is, like all other baboons, from the Old World monkey family. It is one of the largest of all monkeys. Located primarily in southern Africa, the chacma baboon has a wide variety of social behaviors, including a dominance hierarchy, collective foraging, adoption of young by females, and friendship pairings. These behaviors form parts of a complex evolutionary ecology. In general, the species is not threatened, but human population pressure has increased contact between humans and baboons. Hunting, accidents, and trapping kill or remove many baboons from the wild, thereby reducing baboon numbers and disrupting their social structure.
Due to hybridization between different baboon (Papio) populations across Africa, authors have occasionally grouped the entire radiation as a single species, the hamadryas baboon, Papio hamadryas. Arbitrary boundaries were then used to separate the populations into subspecies. Other authors considered the chacma baboon a subspecies of the yellow baboon, Papio cynocephalus, though it is now recognised as a separate species, Papio ursinus. The chacma baboon has two or three subspecies, depending on which classification is followed. Grubb et al. (2003) listed two subspecies,[4] while Groves (2005) in Mammal Species of the World listed three. This article follows Groves (2005) and describes three distinct subspecies. In the Grubb et al. (2003) paper, P. u. raucana was believed to be synonymous with P. u. ursinus.
Papio ursinus ursinus Kerr, 1792 – Cape chacma (found in southern South Africa)
P. ursinus griseipes Pocock, 1911 – Gray-footed chacma (found in northern South Africa to southern Zambia)
P. ursinus raucana Shortridge, 1942 – Ruacana chacma (found from Namibia to southern Angola, but not accepted by all authorities as distinct.
The chacma baboon is perhaps the longest species of monkey, with a male body length of 50–115 cm (20–45 in) and tail length of 45–84 cm (18–33 in). It also one of the heaviest; the male weighs from 21 to 45 kg (46 to 99 lb) with an average of 31.8 kg (70 lb). Baboons are sexually dimorphic, and females are considerably smaller than males. The female chacma weighs from 12 to 25 kg (26 to 55 lb), with an average of 15.4 kg (34 lb). It is similar in size to the olive baboon, averaging slightly higher in mean body mass, and of similar weight to the more compact mandrill, the males of which weigh on average about 1 kg (2.2 lb) more than a chacma baboon, the females weigh 3 kg (6.6 lb) less than the female chacma. While the mandrill is usually crowned the largest of all modern monkeys, going on total length and average (but not maximum) body weight between the sexes, the chacma baboon appears to be the largest extant monkey. The chacma baboon is generally dark brown to gray in color, with a patch of rough hair on the nape of its neck. Unlike the males of northern baboon species (the Guinea, hamadryas, and olive baboons), chacma males do not have a mane. Perhaps the most distinctive feature of this baboon is its long, downward-sloping face. The canine teeth of male chacma baboons have a mean length of 3.86 ± 0.30 cm (1.52 ± 0.12 in) at the time they emigrate from their natal troop. This is the time of greatest tooth length as the teeth tend to wear or be broken thereafter.
The three subspecies are differentiated by size and color. The Cape chacma is a large, heavy, dark-brown, and has black feet. The gray-footed chacma is slightly smaller than the Cape chacma, lighter in color and build, and has gray feet. The Ruacana chacma generally appears to be a smaller, less darkly colored version of the Cape chacma.
The chacma baboon inhabits a wide array of habitats including woodland, savanna, steppes, and subdesert, from the grassy alpine slopes of the Drakensberg to the Kalahari desert. During the night the chacma baboon needs hills, cliffs, or large trees in which to sleep. During the day water availability may limit its range in arid areas. It is found in southern Africa, ranging from South Africa north to Angola, Zambia, and Mozambique. The subspecies are divided across this range. The Cape chacma is found in southern South Africa; the gray-footed chacma, is present from northern South Africa, through the Okavango Delta in Botswana, Zimbabwe, Mozambique (south of the Zambezi), to southwest Zambia; and the Ruacana chacma is found in northern Namibia and southern Angola.
The chacma baboon is omnivorous with a preference for fruits, while also eating insects, seeds, grass, smaller vertebrate animals, and fungi (the desert truffle Kalaharituber pfeilii); at the Cape of Good Hope in particular, it is also known for taking shellfish and other marine invertebrates. It is generally a scavenger when it comes to game meat, and rarely engages in hunting large animals. One incident of a chacma baboon killing a human infant has been reported, but the event is so rare, the locals believed it was due to witchcraft. Normally, chacma baboons will flee at the approach of humans, though this is changing due to the easy availability of food near human dwellings.
The chacma baboon usually lives in social groups, called troops, which are composed of multiple adult males, adult females, and their offspring. Occasionally, however, very small groups form that consist of only a single adult male and several adult females. Chacma troops are characterized by a dominance hierarchy. Female ranking within the troop is inherited through the mother and remains relatively fixed, while male ranking is often in flux, especially when the dominant male is replaced. Chacmas are unusual among baboons in that neither males nor females form strong relationships with members of the same sex. Instead, the strongest social bonds are often between unrelated adult males and females. Infanticide is also common compared to other baboon species, as newly dominant males will often attempt to kill young baboons sired by the previously dominant male. Baboon troops possess a complex group behavior and communicate by means of body attitudes, facial expressions, vocalizations and touch.
The chacma baboon often sleeps in large groups on cliffs or in trees at night to avoid predators. The morning dispersal from the sleeping site is synchronized, with all members leaving at the same time. In most cases, dispersal is initiated by a single individual, and the other members of the group decide whether or not to follow. At least five followers must be recruited for a successful dispersal initiation, and not all initiation attempts are successful. Surprisingly, the initiator's dominance status shows little correlation with successful initiation of departure; more-dominant individuals are no more likely to lead a successful departure than subordinate individuals. One study has shown that while the success rate of dispersal initiation attempts is relatively constant across all sexes, male are more likely to attempt initiation than females, and lactating females are less likely to attempt initiation than females without dependent offspring. A separate study has achieved slightly different results. While dominance hierarchy does not play a significant role in initiating the morning dispersal, social affiliation does. Chacma baboons that play a more central role in the group (as measured by grooming behavior and time spent with other members) are more likely to be followed during the morning dispersal. This study concluded that group members are more likely to follow the behavior of individuals with which they are closely affiliated.
Dominance does play a role in group foraging decisions. A dominant individual (usually the alpha male) leads the group to easily monopolized resources. The group usually follows, even though many subordinate members cannot gain access to that particular resource. As in morning dispersal, the inclination of group members to follow the leader is positively associated with social interactions with that dominant individual.
Collective foraging behavior, with many individuals taking advantage of the same resource at once, has also been observed. However, this behavior can be chiefly attributed to shared dietary needs rather than social affiliation. Pregnant females, who share similar dietary needs, are more likely to synchronize their behavior than fertile females. Foraging synchronization decreases in areas with lower food density.
Adoption behavior has been observed in chacma baboons. Orphaned baboons whose mothers have disappeared or died are often too small to care for themselves. In one study of nine natural orphans and three introduced orphans, all but one orphan were adopted by another member of the group. The individual that was not adopted was 16 months old, four months older than the next oldest orphan, and was old enough to survive on its own. Adoption behavior includes sleeping close to the orphaned infant, grooming and carrying the orphan, and protecting it from harassment by other members of the troop. Both males and females care for infants, and care does not depend on the infant's sex. Additionally, all caregivers are prereproductive, only four or five years of age. The two major theories explaining this behavior are kin selection, in which caregivers take care of potentially related orphans, and parental practice, in which young caregivers increase their own fitness by using an orphan to practice their own parental skills.
Males and female chacma baboons often form relationships referred to as "friendships". These cooperative relationships generally occur between lactating females and adult males. The females are believed to seek out male friendships to gain protection from infanticide. In many baboon species, immigrant alpha males often practice infanticide upon arrival in a new troop. By killing unrelated infants, the new male shortens the time until he can mate with the females of the troop. A female with dependent offspring generally does not become sexually receptive until she weans her offspring at around 12 months of age. However, a mother usually becomes sexually receptive shortly after the death of her offspring.
This protection hypothesis is supported by studies of stress hormones in female baboons during changes in the male hierarchy. When an immigrant male ascends to the top of the male dominance hierarchy, stress hormones in lactating and pregnant females increases, while stress hormones in females not at risk of infanticide stay the same. Additionally, females in friendships with males exhibit a smaller rise in stress hormones than do females without male friends.
The benefits of friendship to males are less clear. A male is more likely to enter into friendships with females with which he has mated, which indicates males might enter into friendships to protect their own offspring and not just to protect that female's future reproductive success. These friendships may play a role in the mating system of chacma baboons. A female will often mate with several males, which increases the number of potential fathers for her offspring and increases the chances she will be able to find at least one friend to protect her infants.
Female chacma baboons have been observed to compete with each other for male friends. This may be the result of one male having a high probability of paternity with multiple females. These competitions are heavily influenced by the female dominance hierarchy, with dominant females displacing subordinate females in friendships with males. Generally, when a more-dominant female attempts to make friends with an individual which is already the friend of a subordinate female, the subordinate female reduces grooming and spatial proximity to that male, potentially leaving her offspring at higher risk of infanticide.
The chacma baboon is widespread and does not rank among threatened animal species. However, in some confined locations, such as South Africa's Southern Cape Peninsula, local populations are dwindling due to habitat loss and predation from other protected species, such as leopards and lions. Some troops have become a suburban menace, overturning trash cans and entering houses in their search for food. These troops can be aggressive and dangerous, and such negative encounters have resulted in hunting by frustrated local residents. This isolated population is thought to face extinction within 10 years.
The chacma is listed under Appendix II of CITES as it occurs in many protected areas across its range. The only area in South Africa where they are monitored is in the Cape Peninsula, where they are protected.
Observations by those working hands-on in South Africa's rehabilitation centers have found this species is damaged by human intervention; troop structures are influenced, and over the years a significant loss in numbers has occurred. Because they live near human habitats, baboons are shot, poisoned, electrocuted, run over, and captured for the pet industry, research laboratories and muthi (medicine).[32] Despite this, assessors working for the IUCN believe there are no major threats that could result in a range-wide decline of the species.
(Wikipedia)
Der Bärenpavian oder Tschakma (Papio ursinus) ist eine Primatenart aus der Gattung der Paviane innerhalb der Familie der Meerkatzenverwandten (Cercopithecidae). Er lebt im südlichen Afrika.
Mit einer Kopfrumpflänge von bis zu 115 Zentimetern, wozu noch ein bis zu 71 Zentimeter langer Schwanz kommt, und einem Gewicht von 15 bis 31 Kilogramm bilden sie die größte und schwerste Pavianart. Ihr Fell ist an der Oberseite dunkelbraun oder grau gefärbt, die Unterseite ist heller, die Hände und Füße sind meist schwarz. Die langgezogene, unbehaarte Schnauze ist dunkelviolett oder schwarz gefärbt, ebenso die Sitzschwielen. Die Fellfärbung und die Größe sind nach Region variabel, so gibt es eine Population mit grauen Pfoten; besonders kleine Exemplare kommen zum Beispiel in der Kalahari vor.
Die Männchen sind deutlich größer und schwerer als die Weibchen und haben auch längere Eckzähne, im Gegensatz zu den übrigen Pavianarten fehlt ihnen aber die Mähne an den Schultern und am vorderen Rücken.
Bärenpaviane leben im südlichen Afrika, genauer in Angola, Botswana, Mosambik, Namibia, Südafrika und Sambia. Sie bewohnen sowohl Steppen und Savannen als auch offene Waldgebiete, sind jedoch auf das Vorhandensein von Wasser angewiesen.
Wie alle Paviane leben sie in Gruppen, meistens in gemischten Gruppen, in manchen Regionen (zum Beispiel im gebirgigen Südafrika) dominieren jedoch die Einmännchengruppen (siehe Gruppenverhalten der Paviane). Die Bärenpaviane zeigen ein komplexes Gruppenverhalten und kommunizieren mittels Körperhaltungen, Gesichtsausdrücken, Lauten und durch Körperkontakte. Bärenpaviane sind Allesfresser; sie haben eine Vorliebe für Früchte, nehmen jedoch auch Blätter, Insekten, Samen und kleinere Wirbeltiere zu sich.
Die Fortpflanzung kann das ganze Jahr über erfolgen, die Weibchen weisen während der fruchtbaren Phase eine ausgeprägte Regelschwellung auf. Innerhalb der gemischten Gruppen kann sich prinzipiell jedes Männchen mit jedem Weibchen paaren. Das führt zu teilweise erbitterten Auseinandersetzungen unter den Männchen um das Paarungsvorrecht.
Nach einer rund 180-tägigen Tragzeit bringt das Weibchen meist ein einzelnes Jungtier zur Welt, das zunächst schwarz gefärbt ist. Mit rund einem Jahr werden die Jungen entwöhnt, mit drei bis fünf Jahren tritt die Geschlechtsreife ein. Das Höchstalter eines Tieres in menschlicher Obhut betrug 45 Jahre, in freier Wildbahn ist die Lebenserwartung deutlich geringer.
Bärenpaviane sind weit verbreitet und zählen nicht zu den bedrohten Tierarten. Manchmal gelten sie als Plage, da sie Plantagen verwüsten.
In Uitenhage war in der zweiten Hälfte des 19. Jahrhunderts ein Bärenpavian namens Jack Assistent eines körperbehinderten Streckenwärters.
(Wikipedia)
Hometown: New York City
Degree: PhD, ecology and evolutionary biology
Julia Bradley-Cook has long been captivated by extreme environments and the way humans interact with them. At Dartmouth, she researched permafrost soils in Greenland to understand climate change impacts on the large carbon pool that the soils contain. Julia was a National Science Foundation IGERT Polar Environmental Change Fellow and a GK-12 Fellow, and pursued science communication through blogging, video, and teaching. As a student leader, she served as president of the Graduate Student Council and co-founded the Science Technology and Engineering Policy Society. Bradley-Cook grew up in New York City and, at age 17, spent 40 days canoeing in the Canadian Arctic. After earning a BA in biology from Grinnell College, she spent two years working at a Namibian nongovernmental organization, supporting research in the Namib Desert and investigating energy use and carbon offset markets. After graduation, Bradley-Cook will return to Washington, D.C., where she is an AAAS Congressional Science Fellow.
Favorite place on campus: The Robert Frost statue
“Only a short walk from the Fairchild science cluster, Robert’s shaded perch never failed to clear my head and give me a fresh perspective.”
(Photo by Joe Martinez)
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An evolutionary process in plain sight.
The vast volcanic sand dunes are too acidic for trees and bushes to thrive, but after years, during rainy season ferns grow and cover the entire area, for a while, until all dried up again. Dried ferns changed the qualities of the soil and grass could thrive in some area, a slow process where mother earth 🌎 allows the volcanic ash turns into fertile land.
Picture taken from the savanna, Mount Bromo, Tengger Semeru National Park, East Java, Indonesia.
Fish, any of approximately 34,000 species of vertebrate animals (phylum Chordata) found in the fresh and salt waters of the world. Living species range from the primitive jawless lampreys and hagfishes through the cartilaginous sharks, skates, and rays to the abundant and diverse bony fishes. Most fish species are cold-blooded; however, one species, the opah (Lampris guttatus), is warm-blooded.
The term fish is applied to a variety of vertebrates of several evolutionary lines. It describes a life-form rather than a taxonomic group. As members of the phylum Chordata, fish share certain features with other vertebrates. These features are gill slits at some point in the life cycle, a notochord, or skeletal supporting rod, a dorsal hollow nerve cord, and a tail. Living fishes represent some five classes, which are as distinct from one another as are the four classes of familiar air-breathing animals—amphibians, reptiles, birds, and mammals. For example, the jawless fishes (Agnatha) have gills in pouches and lack limb girdles. Extant agnathans are the lampreys and the hagfishes. As the name implies, the skeletons of fishes of the class Chondrichthyes (from chondr, “cartilage,” and ichthyes, “fish”) are made entirely of cartilage. Modern fish of this class lack a swim bladder, and their scales and teeth are made up of the same placoid material. Sharks, skates, and rays are examples of cartilaginous fishes. The bony fishes are by far the largest class. Examples range from the tiny seahorse to the 450-kg (1,000-pound) blue marlin, from the flattened soles and flounders to the boxy puffers and ocean sunfishes. Unlike the scales of the cartilaginous fishes, those of bony fishes, when present, grow throughout life and are made up of thin overlapping plates of bone. Bony fishes also have an operculum that covers the gill slits.
The study of fishes, the science of ichthyology, is of broad importance. Fishes are of interest to humans for many reasons, the most important being their relationship with and dependence on the environment. A more obvious reason for interest in fishes is their role as a moderate but important part of the world’s food supply. This resource, once thought unlimited, is now realized to be finite and in delicate balance with the biological, chemical, and physical factors of the aquatic environment. Overfishing, pollution, and alteration of the environment are the chief enemies of proper fisheries management, both in fresh waters and in the ocean. (For a detailed discussion of the technology and economics of fisheries, see commercial fishing.) Another practical reason for studying fishes is their use in disease control. As predators on mosquito larvae, they help curb malaria and other mosquito-borne diseases.
Fishes are valuable laboratory animals in many aspects of medical and biological research. For example, the readiness of many fishes to acclimate to captivity has allowed biologists to study behaviour, physiology, and even ecology under relatively natural conditions. Fishes have been especially important in the study of animal behaviour, where research on fishes has provided a broad base for the understanding of the more flexible behaviour of the higher vertebrates. The zebra fish is used as a model in studies of gene expression.
There are aesthetic and recreational reasons for an interest in fishes. Millions of people keep live fishes in home aquariums for the simple pleasure of observing the beauty and behaviour of animals otherwise unfamiliar to them. Aquarium fishes provide a personal challenge to many aquarists, allowing them to test their ability to keep a small section of the natural environment in their homes. Sportfishing is another way of enjoying the natural environment, also indulged in by millions of people every year. Interest in aquarium fishes and sportfishing supports multimillion-dollar industries throughout the world.
Fishes have been in existence for more than 450 million years, during which time they have evolved repeatedly to fit into almost every conceivable type of aquatic habitat. In a sense, land vertebrates are simply highly modified fishes: when fishes colonized the land habitat, they became tetrapod (four-legged) land vertebrates. The popular conception of a fish as a slippery, streamlined aquatic animal that possesses fins and breathes by gills applies to many fishes, but far more fishes deviate from that conception than conform to it. For example, the body is elongate in many forms and greatly shortened in others; the body is flattened in some (principally in bottom-dwelling fishes) and laterally compressed in many others; the fins may be elaborately extended, forming intricate shapes, or they may be reduced or even lost; and the positions of the mouth, eyes, nostrils, and gill openings vary widely. Air breathers have appeared in several evolutionary lines.
Many fishes are cryptically coloured and shaped, closely matching their respective environments; others are among the most brilliantly coloured of all organisms, with a wide range of hues, often of striking intensity, on a single individual. The brilliance of pigments may be enhanced by the surface structure of the fish, so that it almost seems to glow. A number of unrelated fishes have actual light-producing organs. Many fishes are able to alter their coloration—some for the purpose of camouflage, others for the enhancement of behavioral signals.
Fishes range in adult length from less than 10 mm (0.4 inch) to more than 20 metres (60 feet) and in weight from about 1.5 grams (less than 0.06 ounce) to many thousands of kilograms. Some live in shallow thermal springs at temperatures slightly above 42 °C (100 °F), others in cold Arctic seas a few degrees below 0 °C (32 °F) or in cold deep waters more than 4,000 metres (13,100 feet) beneath the ocean surface. The structural and, especially, the physiological adaptations for life at such extremes are relatively poorly known and provide the scientifically curious with great incentive for study.
Almost all natural bodies of water bear fish life, the exceptions being very hot thermal ponds and extremely salt-alkaline lakes, such as the Dead Sea in Asia and the Great Salt Lake in North America. The present distribution of fishes is a result of the geological history and development of Earth as well as the ability of fishes to undergo evolutionary change and to adapt to the available habitats. Fishes may be seen to be distributed according to habitat and according to geographical area. Major habitat differences are marine and freshwater. For the most part, the fishes in a marine habitat differ from those in a freshwater habitat, even in adjacent areas, but some, such as the salmon, migrate from one to the other. The freshwater habitats may be seen to be of many kinds. Fishes found in mountain torrents, Arctic lakes, tropical lakes, temperate streams, and tropical rivers will all differ from each other, both in obvious gross structure and in physiological attributes. Even in closely adjacent habitats where, for example, a tropical mountain torrent enters a lowland stream, the fish fauna will differ. The marine habitats can be divided into deep ocean floors (benthic), mid-water oceanic (bathypelagic), surface oceanic (pelagic), rocky coast, sandy coast, muddy shores, bays, estuaries, and others. Also, for example, rocky coastal shores in tropical and temperate regions will have different fish faunas, even when such habitats occur along the same coastline.
Although much is known about the present geographical distribution of fishes, far less is known about how that distribution came about. Many parts of the fish fauna of the fresh waters of North America and Eurasia are related and undoubtedly have a common origin. The faunas of Africa and South America are related, extremely old, and probably an expression of the drifting apart of the two continents. The fauna of southern Asia is related to that of Central Asia, and some of it appears to have entered Africa. The extremely large shore-fish faunas of the Indian and tropical Pacific oceans comprise a related complex, but the tropical shore fauna of the Atlantic, although containing Indo-Pacific components, is relatively limited and probably younger. The Arctic and Antarctic marine faunas are quite different from each other. The shore fauna of the North Pacific is quite distinct, and that of the North Atlantic more limited and probably younger. Pelagic oceanic fishes, especially those in deep waters, are similar the world over, showing little geographical isolation in terms of family groups. The deep oceanic habitat is very much the same throughout the world, but species differences do exist, showing geographical areas determined by oceanic currents and water masses.
All aspects of the life of a fish are closely correlated with adaptation to the total environment, physical, chemical, and biological. In studies, all the interdependent aspects of fish, such as behaviour, locomotion, reproduction, and physical and physiological characteristics, must be taken into account.
Correlated with their adaptation to an extremely wide variety of habitats is the extremely wide variety of life cycles that fishes display. The great majority hatch from relatively small eggs a few days to several weeks or more after the eggs are scattered in the water. Newly hatched young are still partially undeveloped and are called larvae until body structures such as fins, skeleton, and some organs are fully formed. Larval life is often very short, usually less than a few weeks, but it can be very long, some lampreys continuing as larvae for at least five years. Young and larval fishes, before reaching sexual maturity, must grow considerably, and their small size and other factors often dictate that they live in a habitat different than that of the adults. For example, most tropical marine shore fishes have pelagic larvae. Larval food also is different, and larval fishes often live in shallow waters, where they may be less exposed to predators.
After a fish reaches adult size, the length of its life is subject to many factors, such as innate rates of aging, predation pressure, and the nature of the local climate. The longevity of a species in the protected environment of an aquarium may have nothing to do with how long members of that species live in the wild. Many small fishes live only one to three years at the most. In some species, however, individuals may live as long as 10 or 20 or even 100 years.
Fish behaviour is a complicated and varied subject. As in almost all animals with a central nervous system, the nature of a response of an individual fish to stimuli from its environment depends upon the inherited characteristics of its nervous system, on what it has learned from past experience, and on the nature of the stimuli. Compared with the variety of human responses, however, that of a fish is stereotyped, not subject to much modification by “thought” or learning, and investigators must guard against anthropomorphic interpretations of fish behaviour.
Fishes perceive the world around them by the usual senses of sight, smell, hearing, touch, and taste and by special lateral line water-current detectors. In the few fishes that generate electric fields, a process that might best be called electrolocation aids in perception. One or another of these senses often is emphasized at the expense of others, depending upon the fish’s other adaptations. In fishes with large eyes, the sense of smell may be reduced; others, with small eyes, hunt and feed primarily by smell (such as some eels).
Specialized behaviour is primarily concerned with the three most important activities in the fish’s life: feeding, reproduction, and escape from enemies. Schooling behaviour of sardines on the high seas, for instance, is largely a protective device to avoid enemies, but it is also associated with and modified by their breeding and feeding requirements. Predatory fishes are often solitary, lying in wait to dart suddenly after their prey, a kind of locomotion impossible for beaked parrot fishes, which feed on coral, swimming in small groups from one coral head to the next. In addition, some predatory fishes that inhabit pelagic environments, such as tunas, often school.
Sleep in fishes, all of which lack true eyelids, consists of a seemingly listless state in which the fish maintains its balance but moves slowly. If attacked or disturbed, most can dart away. A few kinds of fishes lie on the bottom to sleep. Most catfishes, some loaches, and some eels and electric fishes are strictly nocturnal, being active and hunting for food during the night and retiring during the day to holes, thick vegetation, or other protective parts of the environment.
Communication between members of a species or between members of two or more species often is extremely important, especially in breeding behaviour (see below Reproduction). The mode of communication may be visual, as between the small so-called cleaner fish and a large fish of a very different species. The larger fish often allows the cleaner to enter its mouth to remove gill parasites. The cleaner is recognized by its distinctive colour and actions and therefore is not eaten, even if the larger fish is normally a predator. Communication is often chemical, signals being sent by specific chemicals called pheromones.
Many fishes have a streamlined body and swim freely in open water. Fish locomotion is closely correlated with habitat and ecological niche (the general position of the animal to its environment).
Many fishes in both marine and fresh waters swim at the surface and have mouths adapted to feed best (and sometimes only) at the surface. Often such fishes are long and slender, able to dart at surface insects or at other surface fishes and in turn to dart away from predators; needlefishes, halfbeaks, and topminnows (such as killifish and mosquito fish) are good examples. Oceanic flying fishes escape their predators by gathering speed above the water surface, with the lower lobe of the tail providing thrust in the water. They then glide hundreds of yards on enlarged, winglike pectoral and pelvic fins. South American freshwater flying fishes escape their enemies by jumping and propelling their strongly keeled bodies out of the water.
So-called mid-water swimmers, the most common type of fish, are of many kinds and live in many habitats. The powerful fusiform tunas and the trouts, for example, are adapted for strong, fast swimming, the tunas to capture prey speedily in the open ocean and the trouts to cope with the swift currents of streams and rivers. The trout body form is well adapted to many habitats. Fishes that live in relatively quiet waters such as bays or lake shores or slow rivers usually are not strong, fast swimmers but are capable of short, quick bursts of speed to escape a predator. Many of these fishes have their sides flattened, examples being the sunfish and the freshwater angelfish of aquarists. Fish associated with the bottom or substrate usually are slow swimmers. Open-water plankton-feeding fishes almost always remain fusiform and are capable of rapid, strong movement (for example, sardines and herrings of the open ocean and also many small minnows of streams and lakes).
Bottom-living fishes are of many kinds and have undergone many types of modification of their body shape and swimming habits. Rays, which evolved from strong-swimming mid-water sharks, usually stay close to the bottom and move by undulating their large pectoral fins. Flounders live in a similar habitat and move over the bottom by undulating the entire body. Many bottom fishes dart from place to place, resting on the bottom between movements, a motion common in gobies. One goby relative, the mudskipper, has taken to living at the edge of pools along the shore of muddy mangrove swamps. It escapes its enemies by flipping rapidly over the mud, out of the water. Some catfishes, synbranchid eels, the so-called climbing perch, and a few other fishes venture out over damp ground to find more promising waters than those that they left. They move by wriggling their bodies, sometimes using strong pectoral fins; most have accessory air-breathing organs. Many bottom-dwelling fishes live in mud holes or rocky crevices. Marine eels and gobies commonly are found in such habitats and for the most part venture far beyond their cavelike homes. Some bottom dwellers, such as the clingfishes (Gobiesocidae), have developed powerful adhesive disks that enable them to remain in place on the substrate in areas such as rocky coasts, where the action of the waves is great.
The methods of reproduction in fishes are varied, but most fishes lay a large number of small eggs, fertilized and scattered outside of the body. The eggs of pelagic fishes usually remain suspended in the open water. Many shore and freshwater fishes lay eggs on the bottom or among plants. Some have adhesive eggs. The mortality of the young and especially of the eggs is very high, and often only a few individuals grow to maturity out of hundreds, thousands, and in some cases millions of eggs laid.
Males produce sperm, usually as a milky white substance called milt, in two (sometimes one) testes within the body cavity. In bony fishes a sperm duct leads from each testis to a urogenital opening behind the vent or anus. In sharks and rays and in cyclostomes the duct leads to a cloaca. Sometimes the pelvic fins are modified to help transmit the milt to the eggs at the female’s vent or on the substrate where the female has placed them. Sometimes accessory organs are used to fertilize females internally—for example, the claspers of many sharks and rays.
In the females the eggs are formed in two ovaries (sometimes only one) and pass through the ovaries to the urogenital opening and to the outside. In some fishes the eggs are fertilized internally but are shed before development takes place. Members of about a dozen families each of bony fishes (teleosts) and sharks bear live young. Many skates and rays also bear live young. In some bony fishes the eggs simply develop within the female, the young emerging when the eggs hatch (ovoviviparous). Others develop within the ovary and are nourished by ovarian tissues after hatching (viviparous). There are also other methods utilized by fishes to nourish young within the female. In all live-bearers the young are born at a relatively large size and are few in number. In one family of primarily marine fishes, the surfperches from the Pacific coast of North America, Japan, and Korea, the males of at least one species are born sexually mature, although they are not fully grown.
Some fishes are hermaphroditic—an individual producing both sperm and eggs, usually at different stages of its life. Self-fertilization, however, is probably rare.
Successful reproduction and, in many cases, defense of the eggs and the young are assured by rather stereotypical but often elaborate courtship and parental behaviour, either by the male or the female or both. Some fishes prepare nests by hollowing out depressions in the sand bottom (cichlids, for example), build nests with plant materials and sticky threads excreted by the kidneys (sticklebacks), or blow a cluster of mucus-covered bubbles at the water surface (gouramis). The eggs are laid in these structures. Some varieties of cichlids and catfishes incubate eggs in their mouths.
Some fishes, such as salmon, undergo long migrations from the ocean and up large rivers to spawn in the gravel beds where they themselves hatched (anadromous fishes). Some, such as the freshwater eels (family Anguillidae), live and grow to maturity in fresh water and migrate to the sea to spawn (catadromous fishes). Other fishes undertake shorter migrations from lakes into streams, within the ocean, or enter spawning habitats that they do not ordinarily occupy in other ways.
The basic structure and function of the fish body are similar to those of all other vertebrates. The usual four types of tissues are present: surface or epithelial, connective (bone, cartilage, and fibrous tissues, as well as their derivative, blood), nerve, and muscle tissues. In addition, the fish’s organs and organ systems parallel those of other vertebrates.
The typical fish body is streamlined and spindle-shaped, with an anterior head, a gill apparatus, and a heart, the latter lying in the midline just below the gill chamber. The body cavity, containing the vital organs, is situated behind the head in the lower anterior part of the body. The anus usually marks the posterior termination of the body cavity and most often occurs just in front of the base of the anal fin. The spinal cord and vertebral column continue from the posterior part of the head to the base of the tail fin, passing dorsal to the body cavity and through the caudal (tail) region behind the body cavity. Most of the body is of muscular tissue, a high proportion of which is necessitated by swimming. In the course of evolution this basic body plan has been modified repeatedly into the many varieties of fish shapes that exist today.
The skeleton forms an integral part of the fish’s locomotion system, as well as serving to protect vital parts. The internal skeleton consists of the skull bones (except for the roofing bones of the head, which are really part of the external skeleton), the vertebral column, and the fin supports (fin rays). The fin supports are derived from the external skeleton but will be treated here because of their close functional relationship to the internal skeleton. The internal skeleton of cyclostomes, sharks, and rays is of cartilage; that of many fossil groups and some primitive living fishes is mostly of cartilage but may include some bone. In place of the vertebral column, the earliest vertebrates had a fully developed notochord, a flexible stiff rod of viscous cells surrounded by a strong fibrous sheath. During the evolution of modern fishes the rod was replaced in part by cartilage and then by ossified cartilage. Sharks and rays retain a cartilaginous vertebral column; bony fishes have spool-shaped vertebrae that in the more primitive living forms only partially replace the notochord. The skull, including the gill arches and jaws of bony fishes, is fully, or at least partially, ossified. That of sharks and rays remains cartilaginous, at times partially replaced by calcium deposits but never by true bone.
The supportive elements of the fins (basal or radial bones or both) have changed greatly during fish evolution. Some of these changes are described in the section below (Evolution and paleontology). Most fishes possess a single dorsal fin on the midline of the back. Many have two and a few have three dorsal fins. The other fins are the single tail and anal fins and paired pelvic and pectoral fins. A small fin, the adipose fin, with hairlike fin rays, occurs in many of the relatively primitive teleosts (such as trout) on the back near the base of the caudal fin.
The skin of a fish must serve many functions. It aids in maintaining the osmotic balance, provides physical protection for the body, is the site of coloration, contains sensory receptors, and, in some fishes, functions in respiration. Mucous glands, which aid in maintaining the water balance and offer protection from bacteria, are extremely numerous in fish skin, especially in cyclostomes and teleosts. Since mucous glands are present in the modern lampreys, it is reasonable to assume that they were present in primitive fishes, such as the ancient Silurian and Devonian agnathans. Protection from abrasion and predation is another function of the fish skin, and dermal (skin) bone arose early in fish evolution in response to this need. It is thought that bone first evolved in skin and only later invaded the cartilaginous areas of the fish’s body, to provide additional support and protection. There is some argument as to which came first, cartilage or bone, and fossil evidence does not settle the question. In any event, dermal bone has played an important part in fish evolution and has different characteristics in different groups of fishes. Several groups are characterized at least in part by the kind of bony scales they possess.
Scales have played an important part in the evolution of fishes. Primitive fishes usually had thick bony plates or thick scales in several layers of bone, enamel, and related substances. Modern teleost fishes have scales of bone, which, while still protective, allow much more freedom of motion in the body. A few modern teleosts (some catfishes, sticklebacks, and others) have secondarily acquired bony plates in the skin. Modern and early sharks possessed placoid scales, a relatively primitive type of scale with a toothlike structure, consisting of an outside layer of enamel-like substance (vitrodentine), an inner layer of dentine, and a pulp cavity containing nerves and blood vessels. Primitive bony fishes had thick scales of either the ganoid or the cosmoid type. Cosmoid scales have a hard, enamel-like outer layer, an inner layer of cosmine (a form of dentine), and then a layer of vascular bone (isopedine). In ganoid scales the hard outer layer is different chemically and is called ganoin. Under this is a cosminelike layer and then a vascular bony layer. The thin, translucent bony scales of modern fishes, called cycloid and ctenoid (the latter distinguished by serrations at the edges), lack enameloid and dentine layers.
Skin has several other functions in fishes. It is well supplied with nerve endings and presumably receives tactile, thermal, and pain stimuli. Skin is also well supplied with blood vessels. Some fishes breathe in part through the skin, by the exchange of oxygen and carbon dioxide between the surrounding water and numerous small blood vessels near the skin surface.
Skin serves as protection through the control of coloration. Fishes exhibit an almost limitless range of colours. The colours often blend closely with the surroundings, effectively hiding the animal. Many fishes use bright colours for territorial advertisement or as recognition marks for other members of their own species, or sometimes for members of other species. Many fishes can change their colour to a greater or lesser degree, by movement of pigment within the pigment cells (chromatophores). Black pigment cells (melanophores), of almost universal occurrence in fishes, are often juxtaposed with other pigment cells. When placed beneath iridocytes or leucophores (bearing the silvery or white pigment guanine), melanophores produce structural colours of blue and green. These colours are often extremely intense, because they are formed by refraction of light through the needlelike crystals of guanine. The blue and green refracted colours are often relatively pure, lacking the red and yellow rays, which have been absorbed by the black pigment (melanin) of the melanophores. Yellow, orange, and red colours are produced by erythrophores, cells containing the appropriate carotenoid pigments. Other colours are produced by combinations of melanophores, erythrophores, and iridocytes.
The major portion of the body of most fishes consists of muscles. Most of the mass is trunk musculature, the fin muscles usually being relatively small. The caudal fin is usually the most powerful fin, being moved by the trunk musculature. The body musculature is usually arranged in rows of chevron-shaped segments on each side. Contractions of these segments, each attached to adjacent vertebrae and vertebral processes, bends the body on the vertebral joint, producing successive undulations of the body, passing from the head to the tail, and producing driving strokes of the tail. It is the latter that provides the strong forward movement for most fishes.
The digestive system, in a functional sense, starts at the mouth, with the teeth used to capture prey or collect plant foods. Mouth shape and tooth structure vary greatly in fishes, depending on the kind of food normally eaten. Most fishes are predacious, feeding on small invertebrates or other fishes and have simple conical teeth on the jaws, on at least some of the bones of the roof of the mouth, and on special gill arch structures just in front of the esophagus. The latter are throat teeth. Most predacious fishes swallow their prey whole, and the teeth are used for grasping and holding prey, for orienting prey to be swallowed (head first) and for working the prey toward the esophagus. There are a variety of tooth types in fishes. Some fishes, such as sharks and piranhas, have cutting teeth for biting chunks out of their victims. A shark’s tooth, although superficially like that of a piranha, appears in many respects to be a modified scale, while that of the piranha is like that of other bony fishes, consisting of dentine and enamel. Parrot fishes have beaklike mouths with short incisor-like teeth for breaking off coral and have heavy pavementlike throat teeth for crushing the coral. Some catfishes have small brushlike teeth, arranged in rows on the jaws, for scraping plant and animal growth from rocks. Many fishes (such as the Cyprinidae or minnows) have no jaw teeth at all but have very strong throat teeth.
Some fishes gather planktonic food by straining it from their gill cavities with numerous elongate stiff rods (gill rakers) anchored by one end to the gill bars. The food collected on these rods is passed to the throat, where it is swallowed. Most fishes have only short gill rakers that help keep food particles from escaping out the mouth cavity into the gill chamber.
Once reaching the throat, food enters a short, often greatly distensible esophagus, a simple tube with a muscular wall leading into a stomach. The stomach varies greatly in fishes, depending upon the diet. In most predacious fishes it is a simple straight or curved tube or pouch with a muscular wall and a glandular lining. Food is largely digested there and leaves the stomach in liquid form.
Between the stomach and the intestine, ducts enter the digestive tube from the liver and pancreas. The liver is a large, clearly defined organ. The pancreas may be embedded in it, diffused through it, or broken into small parts spread along some of the intestine. The junction between the stomach and the intestine is marked by a muscular valve. Pyloric ceca (blind sacs) occur in some fishes at this junction and have a digestive or absorptive function or both.
The intestine itself is quite variable in length, depending upon the fish’s diet. It is short in predacious forms, sometimes no longer than the body cavity, but long in herbivorous forms, being coiled and several times longer than the entire length of the fish in some species of South American catfishes. The intestine is primarily an organ for absorbing nutrients into the bloodstream. The larger its internal surface, the greater its absorptive efficiency, and a spiral valve is one method of increasing its absorption surface.
Sharks, rays, chimaeras, lungfishes, surviving chondrosteans, holosteans, and even a few of the more primitive teleosts have a spiral valve or at least traces of it in the intestine. Most modern teleosts have increased the area of the intestinal walls by having numerous folds and villi (fingerlike projections) somewhat like those in humans. Undigested substances are passed to the exterior through the anus in most teleost fishes. In lungfishes, sharks, and rays, it is first passed through the cloaca, a common cavity receiving the intestinal opening and the ducts from the urogenital system.
Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills. The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour. Water taken in continuously through the mouth passes backward between the gill bars and over the gill filaments, where the exchange of gases takes place. The gills are protected by a gill cover in teleosts and many other fishes but by flaps of skin in sharks, rays, and some of the older fossil fish groups. The blood capillaries in the gill filaments are close to the gill surface to take up oxygen from the water and to give up excess carbon dioxide to the water.
Most modern fishes have a hydrostatic (ballast) organ, called the swim bladder, that lies in the body cavity just below the kidney and above the stomach and intestine. It originated as a diverticulum of the digestive canal. In advanced teleosts, especially the acanthopterygians, the bladder has lost its connection with the digestive tract, a condition called physoclistic. The connection has been retained (physostomous) by many relatively primitive teleosts. In several unrelated lines of fishes, the bladder has become specialized as a lung or, at least, as a highly vascularized accessory breathing organ. Some fishes with such accessory organs are obligate air breathers and will drown if denied access to the surface, even in well-oxygenated water. Fishes with a hydrostatic form of swim bladder can control their depth by regulating the amount of gas in the bladder. The gas, mostly oxygen, is secreted into the bladder by special glands, rendering the fish more buoyant; the gas is absorbed into the bloodstream by another special organ, reducing the overall buoyancy and allowing the fish to sink. Some deep-sea fishes may have oils, rather than gas, in the bladder. Other deep-sea and some bottom-living forms have much-reduced swim bladders or have lost the organ entirely.
The swim bladder of fishes follows the same developmental pattern as the lungs of land vertebrates. There is no doubt that the two structures have the same historical origin in primitive fishes. More or less intermediate forms still survive among the more primitive types of fishes, such as the lungfishes Lepidosiren and Protopterus.
The circulatory, or blood vascular, system consists of the heart, the arteries, the capillaries, and the veins. It is in the capillaries that the interchange of oxygen, carbon dioxide, nutrients, and other substances such as hormones and waste products takes place. The capillaries lead to the veins, which return the venous blood with its waste products to the heart, kidneys, and gills. There are two kinds of capillary beds: those in the gills and those in the rest of the body. The heart, a folded continuous muscular tube with three or four saclike enlargements, undergoes rhythmic contractions and receives venous blood in a sinus venosus. It passes the blood to an auricle and then into a thick muscular pump, the ventricle. From the ventricle the blood goes to a bulbous structure at the base of a ventral aorta just below the gills. The blood passes to the afferent (receiving) arteries of the gill arches and then to the gill capillaries. There waste gases are given off to the environment, and oxygen is absorbed. The oxygenated blood enters efferent (exuant) arteries of the gill arches and then flows into the dorsal aorta. From there blood is distributed to the tissues and organs of the body. One-way valves prevent backflow. The circulation of fishes thus differs from that of the reptiles, birds, and mammals in that oxygenated blood is not returned to the heart prior to distribution to the other parts of the body.
The primary excretory organ in fishes, as in other vertebrates, is the kidney. In fishes some excretion also takes place in the digestive tract, skin, and especially the gills (where ammonia is given off). Compared with land vertebrates, fishes have a special problem in maintaining their internal environment at a constant concentration of water and dissolved substances, such as salts. Proper balance of the internal environment (homeostasis) of a fish is in a great part maintained by the excretory system, especially the kidney.
The kidney, gills, and skin play an important role in maintaining a fish’s internal environment and checking the effects of osmosis. Marine fishes live in an environment in which the water around them has a greater concentration of salts than they can have inside their body and still maintain life. Freshwater fishes, on the other hand, live in water with a much lower concentration of salts than they require inside their bodies. Osmosis tends to promote the loss of water from the body of a marine fish and absorption of water by that of a freshwater fish. Mucus in the skin tends to slow the process but is not a sufficient barrier to prevent the movement of fluids through the permeable skin. When solutions on two sides of a permeable membrane have different concentrations of dissolved substances, water will pass through the membrane into the more concentrated solution, while the dissolved chemicals move into the area of lower concentration (diffusion).
The kidney of freshwater fishes is often larger in relation to body weight than that of marine fishes. In both groups the kidney excretes wastes from the body, but the kidney of freshwater fishes also excretes large amounts of water, counteracting the water absorbed through the skin. Freshwater fishes tend to lose salt to the environment and must replace it. They get some salt from their food, but the gills and skin inside the mouth actively absorb salt from water passed through the mouth. This absorption is performed by special cells capable of moving salts against the diffusion gradient. Freshwater fishes drink very little water and take in little water with their food.
Marine fishes must conserve water, and therefore their kidneys excrete little water. To maintain their water balance, marine fishes drink large quantities of seawater, retaining most of the water and excreting the salt. Most nitrogenous waste in marine fishes appears to be secreted by the gills as ammonia. Marine fishes can excrete salt by clusters of special cells (chloride cells) in the gills.
There are several teleosts—for example, the salmon—that travel between fresh water and seawater and must adjust to the reversal of osmotic gradients. They adjust their physiological processes by spending time (often surprisingly little time) in the intermediate brackish environment.
Marine hagfishes, sharks, and rays have osmotic concentrations in their blood about equal to that of seawater and so do not have to drink water nor perform much physiological work to maintain their osmotic balance. In sharks and rays the osmotic concentration is kept high by retention of urea in the blood. Freshwater sharks have a lowered concentration of urea in the blood.
Endocrine glands secrete their products into the bloodstream and body tissues and, along with the central nervous system, control and regulate many kinds of body functions. Cyclostomes have a well-developed endocrine system, and presumably it was well developed in the early Agnatha, ancestral to modern fishes. Although the endocrine system in fishes is similar to that of higher vertebrates, there are numerous differences in detail. The pituitary, the thyroid, the suprarenals, the adrenals, the pancreatic islets, the sex glands (ovaries and testes), the inner wall of the intestine, and the bodies of the ultimobranchial gland make up the endocrine system in fishes. There are some others whose function is not well understood. These organs regulate sexual activity and reproduction, growth, osmotic pressure, general metabolic activities such as the storage of fat and the utilization of foodstuffs, blood pressure, and certain aspects of skin colour. Many of these activities are also controlled in part by the central nervous system, which works with the endocrine system in maintaining the life of a fish. Some parts of the endocrine system are developmentally, and undoubtedly evolutionarily, derived from the nervous system.
As in all vertebrates, the nervous system of fishes is the primary mechanism coordinating body activities, as well as integrating these activities in the appropriate manner with stimuli from the environment. The central nervous system, consisting of the brain and spinal cord, is the primary integrating mechanism. The peripheral nervous system, consisting of nerves that connect the brain and spinal cord to various body organs, carries sensory information from special receptor organs such as the eyes, internal ears, nares (sense of smell), taste glands, and others to the integrating centres of the brain and spinal cord. The peripheral nervous system also carries information via different nerve cells from the integrating centres of the brain and spinal cord. This coded information is carried to the various organs and body systems, such as the skeletal muscular system, for appropriate action in response to the original external or internal stimulus. Another branch of the nervous system, the autonomic nervous system, helps to coordinate the activities of many glands and organs and is itself closely connected to the integrating centres of the brain.
The brain of the fish is divided into several anatomical and functional parts, all closely interconnected but each serving as the primary centre of integrating particular kinds of responses and activities. Several of these centres or parts are primarily associated with one type of sensory perception, such as sight, hearing, or smell (olfaction).
The sense of smell is important in almost all fishes. Certain eels with tiny eyes depend mostly on smell for location of food. The olfactory, or nasal, organ of fishes is located on the dorsal surface of the snout. The lining of the nasal organ has special sensory cells that perceive chemicals dissolved in the water, such as substances from food material, and send sensory information to the brain by way of the first cranial nerve. Odour also serves as an alarm system. Many fishes, especially various species of freshwater minnows, react with alarm to a chemical released from the skin of an injured member of their own species.
Many fishes have a well-developed sense of taste, and tiny pitlike taste buds or organs are located not only within their mouth cavities but also over their heads and parts of their body. Catfishes, which often have poor vision, have barbels (“whiskers”) that serve as supplementary taste organs, those around the mouth being actively used to search out food on the bottom. Some species of naturally blind cave fishes are especially well supplied with taste buds, which often cover most of their body surface.
Sight is extremely important in most fishes. The eye of a fish is basically like that of all other vertebrates, but the eyes of fishes are extremely varied in structure and adaptation. In general, fishes living in dark and dim water habitats have large eyes, unless they have specialized in some compensatory way so that another sense (such as smell) is dominant, in which case the eyes will often be reduced. Fishes living in brightly lighted shallow waters often will have relatively small but efficient eyes. Cyclostomes have somewhat less elaborate eyes than other fishes, with skin stretched over the eyeball perhaps making their vision somewhat less effective. Most fishes have a spherical lens and accommodate their vision to far or near subjects by moving the lens within the eyeball. A few sharks accommodate by changing the shape of the lens, as in land vertebrates. Those fishes that are heavily dependent upon the eyes have especially strong muscles for accommodation. Most fishes see well, despite the restrictions imposed by frequent turbidity of the water and by light refraction.
Fossil evidence suggests that colour vision evolved in fishes more than 300 million years ago, but not all living fishes have retained this ability. Experimental evidence indicates that many shallow-water fishes, if not all, have colour vision and see some colours especially well, but some bottom-dwelling shore fishes live in areas where the water is sufficiently deep to filter out most if not all colours, and these fishes apparently never see colours. When tested in shallow water, they apparently are unable to respond to colour differences.
Sound perception and balance are intimately associated senses in a fish. The organs of hearing are entirely internal, located within the skull, on each side of the brain and somewhat behind the eyes. Sound waves, especially those of low frequencies, travel readily through water and impinge directly upon the bones and fluids of the head and body, to be transmitted to the hearing organs. Fishes readily respond to sound; for example, a trout conditioned to escape by the approach of fishermen will take flight upon perceiving footsteps on a stream bank even if it cannot see a fisherman. Compared with humans, however, the range of sound frequencies heard by fishes is greatly restricted. Many fishes communicate with each other by producing sounds in their swim bladders, in their throats by rasping their teeth, and in other ways.
A fish or other vertebrate seldom has to rely on a single type of sensory information to determine the nature of the environment around it. A catfish uses taste and touch when examining a food object with its oral barbels. Like most other animals, fishes have many touch receptors over their body surface. Pain and temperature receptors also are present in fishes and presumably produce the same kind of information to a fish as to humans. Fishes react in a negative fashion to stimuli that would be painful to human beings, suggesting that they feel a sensation of pain.
An important sensory system in fishes that is absent in other vertebrates (except some amphibians) is the lateral line system. This consists of a series of heavily innervated small canals located in the skin and bone around the eyes, along the lower jaw, over the head, and down the mid-side of the body, where it is associated with the scales. Intermittently along these canals are located tiny sensory organs (pit organs) that apparently detect changes in pressure. The system allows a fish to sense changes in water currents and pressure, thereby helping the fish to orient itself to the various changes that occur in the physical environment.
+++ DISCLAIMER +++
Nothing you see here is real, even though the conversion or the presented background story might be based historical facts. BEWARE!
Some background:
The Dassault MD.454 Mystère IV was a 1950s French fighter-bomber aircraft, the first transonic aircraft to enter service in French Air Force. The Mystère IV was an evolutionary development of the Mystère II aircraft and the straight-wing Ouragan. Although bearing an external resemblance to the earlier aircraft, the Mystère IV was in fact a new design with aerodynamic improvements for supersonic flight. The prototype first flew on 28 September 1952, and the aircraft entered service in April 1953.
The first 50 Mystère IVA production aircraft were powered by British Rolls-Royce Tay turbojets, while the remainder had the French-built Hispano-Suiza Verdon 350 version of that engine. In addition to production Mystère IVA, Dassault developed an upgraded Mystère IVB with either a Rolls-Royce Avon (first two prototypes) or a SNECMA Atar 101 (third prototype) afterburning engine and a radar ranging gunsight. Six pre-production aircraft were built but the project was abandoned in favor of the more promising Super Mystère.
Another development was the Mystère IVN. This aircraft was developed in parallel with the Mystère IVB as a night and all-weather interceptor. It differed from the single-seat fighter in several respects: a 1.4m section was added to the forward fuselage to accommodate a second crew member; internal fuel capacity was substantially increased and provision was made for an APG 33 intercept radar with the scanner above the engine air intake, not unlike the North American F-86D 'Sabre Dog' which already flew in 1949.
Powered by a Rolls-Royce Avon RA.7R, rated at 9.553 lbf (43.30 kN) with maximum afterburning, the Mystère IVN had provision for an armament of two 30mm cannons in the lower forward fuselage and a retractable rocket pack for 55 unguided air-air rockets of 68mm caliber.
The prototype was flown on 19 July 1954, but the development program was soon about to be abandoned owing to France's inability to finance the development of two night fighters (the other being the SNCASO Vautour) at the same time. Compared to the heavier Vautour, the Mystère IVN suffered from several shortcomings: endurance was considered insufficient and the proposed APG-33 radar, a Hughes-built Aircraft X band fire control radar originally developed for the USAF's F-89A and F-94A/B 1st generation jet interceptors, turned out to be unsuitable, too.
France decided to move on with the Vautour, but there was serious interest in the Mystère IVN from foreign markets: India, already being a taker of French combat aircraft like the Ouragan and the Mystère IVA, showed much interest, as well as smaller European countries like the Netherlands, Denmark, Germany and Belgium, where the limited range and loiter time were only of secondary importance. Israel also showed much interest. Most of them had to replace their outdated WWII Mosquito night fighters or were looking for a jet-powered, yet affordable solution for the all-weather interceptor role.
Eventually the Mystère IVN was developed further as a private venture, without official orders for the Armée de l’ Air. Several measures were taken to improve the type's endurance – the most significant was to omit the rocket belly tray in the fuselage and its complicated mechanics. Instead, the space was used for an auxiliary tank and some new avionics.
The IVA’s pair of 30mm DEFA cannons was retained. Unguided rockets – at the time of development the preferred air-to-air weapon against large bomber groups, coming in at high altitude and subsonic speed, could still be carried externally in up to four streamlined pods under the wings. A pair of 800l drop tanks could be carried on the wet inner pair of pylons, too.
Avionics were upgraded, too: the prototypes' AN/APG-33 was replaced by a more effective Hughes AN/APG-40 fire control radar (used in the F-89D and F-94C), together with an E-9 fire control system like that of the early F-102. This allowed the Mystère IVN (theoretically) to carry both types of the GAR-1/AIM-4 'Falcon' AAM. The GAR-1D (later re-coded AIM-4A) had semi-active radar homing (SARH), giving a range of about 5 mi (8.0 km). The GAR-2 (AIM-4B) was a heat-seeker, generally limited to rear-aspect engagements, but with the advantage of being a 'fire and forget' weapon. It had a similar range to the GAR-1.
The Mystère IVN could carry a maximum of four such missiles on launch rails under the wings. As would also be Soviet practice, it was common to fire the weapon in salvos of both types to increase the chances of a hit (a heat-seeking missile fired first, followed moments later by a radar-guided missile). The Falcon turned out to be rather unreliable and complicated in handling. It also had only a small 7.6 lb (3.4 kg) warhead, limiting their lethal radius, and it lacked a proximity fuze: the fuzing for the missile was in the leading edges of the wings, requiring a direct hit to detonate. Consequently, the missile was not introduced by any of the Mystère IVN’s users.
Alternatively, the French AA.20 air-to-air missile was tested, but it was deemed to be even less practical, as it relied on direct command guidance, using a similar system to that used by Nord's anti-tank missiles, with the missile being steered visually from the launching aircraft - at night or in adverse weather conditions not a suitable concept. The later, beam-riding AA.25 would have been a better option, but it was incompatible with the US-built APG-40 radar.
Belgium was the initial user of the type, initially buying 24 Mystery IVN (serialled AY-01 – 24) as replacements for the BAF's obsolete Mosquito NF.30 fleet in 1955, and later ordering 12 more as replacements for the Gloster Meteor NF.11 night fighter fleet. These were accompanied by 53 Avro CF-100 'Canuck', bought in 1957.
Both types served with No 11, 349 and 350 Squadron of the 1st "All Weather" Wing at Beauvechain and only saw a single, brief ‘hot’ mission: during “Operation Simba” in 1959, four BAF Mystère IVN, were, together with four more CF-100s, deployed to Kamina Air Base in Belgian Kongo, in order to suppress unrest and keep air control. The mission only lasted from 3rd to 16th of July 1959, though, and the transfer alone took four days, due to slow C-119G transporters which carried the technical support for the mission.
The Canuck was only used until 1964 when it was replaced by the Lockheed F-104G Starfighter, the Belgian Mystère IVNs would follow in 1975. None of these aircraft was preserved, as all remaining aircraft were sold to scrap dealer Van Heyghen and broken up at Gent.
Other users were Israel (20), India (42), Spain (16) and Australia (16) – many European countries rather settled for the license-built F-86K/L interceptors, sponsored by the USA (e. g. Denmark, the Netherlands, Italy, Germany), even though the Mystère IVN offered the benefit of a second crew member/WSO.
General characteristics
Crew: 2
Length: 14.92 m (49 ft 11 in)
Wingspan: 11.12 m (36 ft 5 ¾ in)
Height: 4.60 m (15 ft 1 in)
Wing area: 32.06 m² (345.1 ft²)
Empty weight: 7.140 kg (15.741 lb)
Max. take-off weight: 10.320 kg(22.752 lb)
Powerplant
1× Rolls-Royce Avon RA.7R rated at 7.350 lbf (32.69 kN) dry thrust and 9.553 lbf (43.30 kN) with afterburner
Performance
Maximum speed: 1.030 km/h (640 mph) at sea level
Range: 915 km (494 nmi, 570 mi) without external tanks,
Ferry range: 2.280 km (1.231 nmi, 1.417 mi) with external tanks
Service ceiling: 15.000 m (49.200 ft)
Rate of climb: 95 m/s (7.874 ft/min)
Armament
2× 30 mm (1.18 in) DEFA cannons with 150 rounds per gun
1.000 kg (2.200 lb) of payload on four external hardpoints under the wings, including unguided rocket pods (for 19 x 68mm missiles each), drop tanks, iron bombs of up to 1.000 lb (454 kg) caliber or up to four GAR-1/2 (AIM-4) ‘Falcon’ AAMs.
The kit and its assembly:
A whiffy aircraft – even though it actually existed! This became a bigger project than originally intended – it started when I wondered what one could whif from a Matchbox Mystère IVA? When I browsed sources I stumbled across the real IVN prototype several times, a very attractive aircraft. An all-weather version sounded like a plan.
At first I just wanted to add a radome and a chin air intake to the basic kit, creating a fantasy single-seater, but then I decided to tackle the challenge and create something that could be called a IVN model – even though a later service aircraft, and certainly not 100% true to the real thing.
Another factor that spoke for the IVN was that there is no kit available. AFAIK there’s a short-run, mixed-media 1:48 scale kit from Fonderie Miniatures of this aircraft – but in 1:72?
In real life, only a single Mystère IVN was actually built and flown – the type became a victim to the Vautour, as mentioned above. The only prototype served as a radar and equipment test bed, and AFAIK it still exists today as an exhibit at the Conservatoire de l'Air et de l'Espace d'Aquitaine in Bordeaux–Merignac. As a side note: With this plane Jacqueline Auriol beat the women world speed record in May 1955, flying 1.151 km/h
Basis for my conversion is the simple Matchbox Mystère IVA kit. Good news is that you just need to modify the fuselage for an IVN – wings and tail surfaces can be taken OOB. But the fuselage…?
The easier part is the rear end, as the exhaust pipe needs to be widened and lengthened for the IVN’s bigger afterburner engine. I cut the original tail section under the fin away and replaced it with parts from 1:100 A-10 engine nacelles, with a new nozzle inside and 2C putty sculpting around the fin base in order to get some cleaner lines. Pretty straightforward.
The front end was another thing, though. Almost anything in front of the wings had to be re-designed. Initial step was to lengthen the fuselage by almost exactly 20mm, but then you need the chin air intake with the radome above (very F-86D-like), too, and a tandem seat cockpit has to be integrated. Complicated!
I found a suitable cockpit hood in the Matchbox Meteor NF.11/12/14 kit (Hannant’s Xtrakit re-boxing). It offers, as optional parts for a late NF.14, a strutless, relatively short canopy together with a matching fuselage part. A very convenient combo for the conversion, as the clear parts can be glued onto correct foundations, and even the dorsal radius of Meteor and Mystère is very similar.
After cutting the fuselage in front of the wings in half I also cut out a dorsal gap around the original cockpit opening and tried to insert the donation part, while filling the 20mm gaps on the fuselage flanks with styrene strips on the inside of the fuselage and 2C and finally NC putty on the outside.
In the same step I also had to improvise a new cockpit floor. The dashboard and radar screen for the WSO were taken from the Meteor. I also added cockpit side walls from styrene sheet and ejection seats.
A dorsal spine had to be scratched, too, as the Meteor NF.14 had a bubble canopy, while the Mystère IVN features a straight spine. The canopy was cut at its rear end, and a part of a vintage FROG Me 410 engine nacelle(!) was implanted to fill the spine gap. More messy putty work, but things started to look like the real aircraft!
With the cockpit and the glass parts in place I started sculpting the nose section next. The radome is a WWII drop tank front end, cut out to match the IVA’s nose shape. Then the air intake below was added, it comes from a Italeri F-16 but had to be considerably modified in order to fit into the new place (narrowed, shortened, and with cutout on top for the radome). Being flatter and wider I extended the new intake’s lines and shape into cheek fairings, up to the cannon muzzles.
During the same process I also blended the radome with the circular front end of the original Mystère IVA. Again, lots of putty sculpting, but worth the effort. It’s certainly not 100% like the real thing, but IMHO the impression counts in this case.
The landing gear was taken OOB. Under the wings four pylons were added (from two Revell G.91 kits, the inner pairs), the inner pair received drop tanks (also from a Revell Fiat G.91), the outer pair holds the IVA kit’s streamlined rocket pods, those that come OOB.
For those who quibble about the Matchbox kit’s small drop tanks: No, these 'blobs' are typical French air-to-air missile pods of the 50ies/60ies, with 19 68mm missiles inside. They have vertical front and back ends, but they carry aerodynamic caps on both ends. Looks wacky, but if you know what they are they make sense. They can also be seen on contemporary Vautour aircraft.
In a wake of terminal detailism I also decided to modify the wings with lowered flaps – this is easy to realize, since area under the wings is limited by wide and deep trenches, and the flaps are just “boards”. The respective areas were sanded away, and new flaps made from thin styrene sheet.
Several pitots from wire or styrene were added, the gun ports drilled open and filled witn short pieces of hollow steel needles.
Painting and markings:
A French service aircraft would have been the 1st choice, but all aircraft from that era were left bare metal – with the rough putty surface not the best choice, and it might have looked rather F-86D-style?
Camouflaged French aircraft came later, with the imported F-100s and the SMB2, and those were rather tactical schemes.
So, I looked for an alternative, also in foreign countries, and settled on Belgium. The real Belgian Air Force situation is described above, and one can only wonder why they settled for the huge and rather ineffective CF-100, as it only carried unguided air-to-air rockets on the wing tips, but no cannon at all. So, there would have been a place for a smaller and more agile night fighter in the BAF.
The paint scheme follows the BAF’s fashion of the late 1950ies: RAF-style, featuring a rather dark green/dark grey camouflage, with pale grey the lower surfaces, but not in BS colors, rather European NATO standard.
I settled for Revell 46 (RAL 6014, NATO olive green) and Modelmaster 2085 (actually RLM 75 - it is a tad lighter than Dark Sea Grey) as basic colors for the upper sides, and Modelmaster 2039 (FS 16515, Canadian Voodoo Grey) for the lower sides. This sounds like an odd combo, but after consulting real aircraft pics of that era the colors seemed to deteriorate quickly, esp. the green would bleach into even reddish hues and the grey turn very pale.
Consequently the aircraft was weathered thoroughly through dry-brushing the upper sides and the panel lines with several lighter tones. The green received a treatment with RLM 81(!) and Humbrol 155, esp. around the hot rear end of the afterburner extension, and the grey was lightened with Dark Sea Grey and FS 36231.
The kit also received a light black ink wash in order to emphasize contrasts - most details were painted onto the hull, as I didn't dare a new engraving on the mixed material underground.
After painting was done I could not help but consider the camouflaged Mystère IVN to look like a blown-up Fiat G.91T? Weird how a paint scheme affects perception! To be honest, I don’t find the paint scheme truly sexy, but together with the Belgian cockades and the red 350th Squadron markings the aircraft looks disturbing enough to make you look twice.
The cockpit interior was painted in dark grey, the landing gear wells and other interior surfaces were left in Aluminum.
The red and white wing tip pitots are a nice, colorful detail. I am not certain if these were unique to the IVN prototype, but I adopted them for my service version – and the stripes were taken from real world BAF CF-100s.
Tactical codes were improvised with single letters from TL Modellbau sheets. The squadron marking decals come from a Modeldecal aftermarket sheet (#100), they belong to a Belgian CF-100.
The roundels were partly taken from the same sheet, but also from a TL Modellbau roundels sheet, as the CF-100 insignia were much too large for the relatively compact Mystère IVN.
A messy project, since almost the whole fuselage had to be modified – but worth the effort. The Mystère IVN is a pretty aircraft that unfortunately did not get its chance.
The bright Belgian roundels (esp. those on the wings, with their blue, wide extra ring!) make the aircraft look a bit surreal? Anyway, the NATO camouflage makes the Mystère IVA heritage almost disappear, I guess that the aircraft will confuse a lot of people. ;)
What is the truth about Darwinian, progressive (microbes to human) evolution?
Although we are told it is an irrefutable, scientific fact .....
the real fact, as we will show later, is that there is no credible mechanism for such progressive evolution.
Classical Darwinism: Evolution by creeps.
What was the evolutionary idea that Darwin popularised?
Put simply ...
Darwin believed that there was unlimited variability in the gene pool of all living things, which would enable the gradual transformation of a first, self-replicating, living cell, through many years of natural selection, into every living thing, including humans.
However, the changes possible were well known by selective breeders to be strictly limited.
This is because the changes seen in selective breeding are due to the shuffling, deletion and emphasis, or duplication, of genetic information already existing in the gene pool (micro-evolution). There is no viable mechanism for creating new, beneficial, genetic information required to create entirely new body parts ... anatomical structures, biological systems, organs etc. (macro-evolution).
Darwin rashly ignored the limits which were well known to breeders (even though he selectively bred pigeons himself, and should have known better). He simply extrapolated the strictly limited, minor changes observed in selective breeding to major, unlimited, progressive changes able to create new structures, organs etc. through natural selection, over an alleged, multi-million year timescale.
Of course, the length of time involved made no difference, the existing, genetic information could not increase of its own accord, no matter how long the timescale. Natural selection can only select from that which is already there, it cannot create any new information.
That was a gigantic flaw in Darwinism, and opponents of Darwin's ideas tried to argue that changes were limited, as selective breeding had demonstrated. But, because Darwinism had so quickly and widely acquired a status more akin to an ideology than objective science, belief in the Darwinian idea outweighed the verdict of observational and experimental science. Thus classical Darwinism became firmly established as scientific orthodoxy for nearly a century.
Opponents continued to argue all this time, that Darwinism could not be supported scientifically, and should not even merit the status of a scientific theory, but they were ostracised and dismissed as cranks, weirdoes or religious fanatics.
Finally however, it was discovered that the opponents of Darwin were perfectly correct - and that constructive, genetic changes (progressive, macro-evolution) would require the creation of new, genetic information.
This looked like the ignominious end of Darwinism, as there was no credible, natural mechanism able to create new, constructive, genetic information. And Darwinism should have been consigned to the dustbin of history,
However, rather than ditch the whole idea as unscientific nonsense, the vested interests in Darwinism had become so important, with numerous, lifelong careers and an ideological agenda which depended on the Darwinian belief system, a desperate attempt was made to rescue it from its justified demise.
A mechanism had to be invented to explain the origin of new, constructive information.
That mechanism was 'mutations'. Mutations are ... literally, genetic, copying MISTAKES.
Enter Neo-Darwinism: Evolution by freaks.
Because the majority of the public had already been convinced that classical Darwinism was a scientific fact, and that anyone who questioned it was undoubtedly a crank, all that had to be done, as far as the public was concerned, was to give the impression that the ‘theory’ had been refined and updated in the light of modern science.
The true fact that classical Darwinism had always been demonstrably wrong and was fatally flawed from the outset, was kept quiet. This meant that the opponents of Darwinism, who had been correct all along, and who were the real champions of science, continued to be ridiculed and vilified as cranks and scorned by the mass media and the establishment.
The new developments were portrayed simply as an updating of the ‘theory’. The impression was given that there was nothing wrong with Darwin’s original idea of progressive (macro) evolution, it had simply 'evolved' and 'improved' in the light of greater knowledge ....
A sort of progressive evolution of the whole idea of evolution.
This new, 'improved' Darwinism became known as Neo-Darwinism.
So, what is Neo-Darwinism? And did it really solve the fatal flaws of the Darwinian idea?
Neo Darwinism is progressive, macro evolution - as Darwin had proposed, but based on the (ludicrous) idea that random mutations (which are accidental, genetic, copying mistakes) selected by natural selection, can provide the constructive, genetic information capable of creating entirely new features, anatomical structures, organs, and biological systems. In other words, it is macro-evolution based on a belief in the progression from microbes to humans through billions of random, genetic, copying MISTAKES, accumulated over many millions of years.
However, there is no evidence for it, and it should be classed as unscientific nonsense, it defies logic, the laws of probability and Information Theory.
It is understandable that people can be confused, because they know that 'micro'-evolution is an observable fact, which everyone accepts. It is a disgrace that evolutionists cynically exploit that confusion by citing obvious examples of micro-evolution such as: the Peppered Moth, Darwin's finches, so-called superbugs etc., as evidence of macro-evolution.
Such examples are not evidence of macro-evolution at all. The public is being hoodwinked and lied to. There are no observable examples or evidence of macro-evolution, and no examples of a mutation, or a series of mutations, capable of creating new anatomical structures, organs etc. and that is a fact. It is no wonder that the distinguished entomologist, W R Thompson wrote in the preface to the 1959 centenary edition of Darwin's Origin of the Species, that ... “the success of Darwinism was accompanied by a decline in scientific integrity.”
Micro-evolution is just the small changes which take place, through natural selection or selective breeding, but only within the strict limits of the built-in variability of the existing gene pool. Any constructive changes, outside the extent of the existing gene pool, requires a credible mechanism for the creation of new, beneficial, constructive, genetic information. That is essential for ‘macro’ evolution. And that is a massive problem.
Micro evolution does not involve or require the creation of any new, genetic information. Therefore, micro evolution and macro evolution are entirely different. Apart from the idea that both require natural selection, there is no other connection, whatever evolutionists may claim.
Once people fully understand that the differences they see in various, dog breeds, for example, are just limited micro-evolution (selection of existing, genetic information) and nothing to do with progressive macro-evolution, they realise that they have been fed an incredible story.
A dog will always remain a dog, it can never be selectively bred into some other creature, the extent of variation is constrained by the limitations of the existing, genetic information in the gene pool of the dog genus, and fully, informed evolutionists know that is an irrefutable fact.
To explain further.... Neo-Darwinian, macro evolution is the incredible idea that everything in the genome of humans, and every living thing past and present (apart from the original genetic information in the very first living cell) , is purely the result of the accumulation of billions of genetic, copying mistakes..... mutations accrued upon previous mutations, and on - and on - and on.
Although evolutionists don’t like to state it this way, Neo-Darwinism actually proposes that the complete genome (every scrap of genetic information in the DNA) of every living thing that has ever lived was created by a long series of cumulative mistakes ... mistakes upon previous mistakes .... upon previous mistakes .... upon previous mistakes etc. etc. In other words, the complete genome of every living thing is made up of nothing more than an incredibly long chain of mistakes. That is the mind-boggling truth about the neo-Darwinian, evolution story. For obvious reasons, it is something evolutionists would prefer you not to think about too much.
When we do think about it, we soon realise that what is actually being proposed is that, apart from the original information in the first living cell (and evolutionists have yet to explain how that original information magically arose?) - every additional scrap of genetic information for all - biological features, anatomical structures, systems and processes that exist, or have ever existed in living things, such as:
skin, bones, bone joints, shells, flowers, leaves, wings, scales, muscles, fur, hair, teeth, claws, toe and finger nails, horns, beaks, nervous systems, blood, blood vessels, brains, lungs, hearts, digestive systems, vascular systems, liver, kidneys, pancreas, bowels, immune systems, senses, eyes, ears, sex organs, sexual reproduction, sperm, eggs, pollen, the process of metamorphosis, marsupial pouches, marsupial embryo migration, mammary glands, hormone production, melanin etc. .... have been created entirely from scratch, by an incredibly long series of small, accumulated mistakes ... mistake - upon mistake - upon mistake - upon mistake - over and over again, millions of times.
That is ... every body part, system and process of all living things are the result of literally billions of genetic MISTAKES of MISTAKES, accumulated over many millions of years.
Incredibly, what we are asked to believe is that something like a vascular system, reproductive organs, or something like the process of insect metamorphosis, developed in small, random, incremental steps, with every step being the result of a copying mistake, and with each step being able to provide a significant survival or reproductive advantage in order to be preserved and become dominant in the gene pool.
If you believe that ... you will believe anything.
Even worse, evolutionists have yet to cite a single example of a positive, beneficial, mutation which adds constructive information to the genome of any creature. Yet they expect us to believe that we have been converted from an original, single, living cell into humans by an incredibly, vast accumulation of these imaginary, beneficial mutations.
Conclusion:
Progressive, microbes-to-man evolution is impossible - there is no credible mechanism to produce all the new, genetic information which is essential for that to take place.
The evolution story is an obvious fairy tale presented as scientific fact.
However, nothing has changed - those who dare to question Neo-Darwinism are still portrayed as idiots, retards, cranks, weirdoes, anti-scientific ignoramuses or religious fanatics.
Want to join the club?
What about the fossil record?
The formation of fossils.
Books explaining how fossils are formed frequently give the impression that it takes many years of build up of layers of sediment to bury organic remains, which then become fossilised.
Therefore many people don't realise that this impression is erroneous, because it is a fact that all good, intact fossils require rapid burial in sufficient sediment to prevent decay or predatory destruction.
So it is evident that rock containing good, undamaged fossils was laid down rapidly, sometimes in catastrophic conditions.
The very existence of intact fossils is a testament to rapid burial and sedimentation.
You don't get fossils from slow burial. Organic remains don't just sit around on the sea bed, or elsewhere, waiting for sediment to cover them a millimetre at a time, over a long period.
Unless they are buried rapidly, they would soon be damaged or destroyed by predation and/or decay.
The fact that so many sedimentary rocks contain fossils, indicates that the sediment that created them was normally laid down within a short time.
Another important factor is that many large fossils (tree trunks, large fish, dinosaurs etc.) intersect several or many strata (sometimes called layers) which clearly indicates that multiple strata were formed simultaneously in a single event by grading/segregation of sedimentary particles into distinct layers, and not stratum by stratum over long periods of time or different geological eras, which is the evolutionist's, uniformitarian interpretation of the geological column.
In view of the fact that many large fossils required a substantial amount of sediment to bury them, and the fact that they intersect multiple strata (polystrate fossils), how can any sensible person claim that strata or, for that matter, any fossil bearing rock, could have taken millions of years to form?
What do laboratory experiments and field studies of recent, sedimentation events show? sedimentology.fr/
You don't even need to be a qualified sedimentologist or geologist to come to that conclusion, it is common sense.
Rapid formation of strata - some recent, field evidence:
www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Evolution - multi-million year timescale debunked.
Rapid strata formation in soft sand (field evidence).
www.flickr.com/photos/truth-in-science/39554035561
All creatures and plants alive today, which are found as fossils, are the same in their fossil form as the living examples, in spite of the fact that the fossils are claimed to be millions of years old. So all living things today could be called 'living fossils' inasmuch as there is no evidence of any evolutionary changes in the alleged multi-million year timescale. The fossil record shows either extinct species or unchanged species, that is all.
When no evidence is cited as evidence:
www.flickr.com/photos/101536517@N06/15157133658
The Cambrian Explosion.
Trilobites and other many creatures appeared suddenly in some of the earliest rocks of the fossil record, with no intermediate ancestors. This sudden appearance of a great variety of advanced, fully developed creatures is called the Cambrian Explosion. Trilobites are especially interesting because they have complex eyes, which would need a lot of progressive evolution to develop such advanced features However, there is no evidence of any evolution leading up to the Cambrian Explosion, and that is a serious dilemma for evolutionists.
Trilobites are now thought to be extinct, although it is possible that similar creatures could still exist in unexplored parts of deep oceans.
See fossil of a crab unchanged after many millions of years:
www.flickr.com/photos/101536517@N06/12702046604/in/set-72...
Fossil museum: www.flickr.com/photos/101536517@N06/sets/72157641367196613/
What about all the claimed scientific evidence that evolutionists have found for evolution?
The evolutionist 'scientific' method has resulted in a serious decline in scientific integrity, and has given us such scientific abominations as:
Piltdown Man (a fake),
Nebraska Man (a pig),
South West Colorado Man (a horse),
Orce man (a donkey),
Embryonic Recapitulation (a fraud),
Archaeoraptor (a fake),
Java Man (a giant gibbon),
Peking Man (a monkey),
Montana Man (an extinct dog-like creature)
Nutcracker Man (an extinct type of ape - Australopithecus)
The Horse Series (unrelated species cobbled together),
Peppered Moth (faked photographs)
The Orgueil meteorite (faked evidence)
Etc. etc.
Anyone can call anything 'science' ... it doesn't make it so.
All these examples were trumpeted by evolutionists as scientific evidence for evolution.
Do we want to trust evolutionists claims about scientific evidence, when they have such an appalling record?
Just how good are peer reviews of scientific papers?
www.sciencemag.org/content/342/6154/60.full
Want to publish a science paper?
www.nature.com/nature/journal/v434/n7036/full/nature03653...
www.nature.com/news/publishers-withdraw-more-than-120-gib...
Piltdown Man and Nebraska Man were even used in the famous, Scopes Trial as positive evidence for evolution.
Piltdown Man reigned for over 40 years, as a supreme example of human evolution, before it was exposed as a crudely, fashioned fake.
Is that 'science'?
Punctuated Equilibrium: Evolution by Jerks.
The ludicrous Hopeful Monster Theory and so-called Punctuated Equilibrium (evolution in big jumps) were invented by evolutionists as a desperate attempt to explain away the lack of fossil evidence for evolution. They are proposed methods of evolution which, it is claimed, need no fossil evidence. They are actually an admission that the required fossil evidence does not exist.
Piltdown Man... it survived as alleged proof of evolution for over 40 years in evolution textbooks and was taught in schools and universities, it survived peer reviews etc. and was used as supposed irrefutable evidence for evolution at the famous Scopes Trial..
_____________________________________________
A pig, a horse and a donkey!
The pig ....
Nebraska Man, this was a single tooth of a peccary. it was trumpeted as scientific evidence for the evolution of humans. Highly imaginative artists impressions of an ape-like man appeared in newspapers magazines etc.
Having been 'discovered' 3 years prior to the Scopes Trial, it was resurrected, and given renewed publicity, shortly before the trial - presumably, in order to influence the trial and convince the public of the scientific evidence for evolution.. Such 'scientific' evidence is enough to make any genuine, respectable scientist weep.
The horse ....
South West Colorado Man, another tooth .... of a horse this time... also hailed as ‘scientific’ evidence for human evolution.
The donkey ....
Orce man, loudly proclaimed by evolutionists to be scientific evidence of an early hominid, based on the discovery of a tiny fragment of skullcap. This is now believed to have most likely come from a donkey, but even if it was human. such a tiny fragment is certainly not any evidence of human evolution, as it was claimed. A symposium which had been planned to discuss this alleged human 'missing link' had to be embarrassingly cancelled when it was identified as being very similar to a donkey skull.
_________________________________________
Embryonic Recapitulation, the evolutionist zealot Ernst Haeckel (who was a hero of Hitler) published fraudulent drawings of embryos and his theory was readily accepted by evolutionists as proof of evolution. Even after he was exposed as a fraudster, evolutionists still continued to use his fraudulent evidence in books and publications on evolution, including school textbooks, until very recently.
Archaeoraptor, A so-called feathered dinosaur from the Chinese fossil faking industry. It managed to fool credulous evolutionists, because it was exactly what they were looking for. The evidence fitted the wishful thinking.
Java Man, Dubois, the man who discovered Java Man and declared it a human ancestor ..... admitted much later that it was actually a giant gibbon, however, that spoilt the evolution story which had been built up around it, so evolutionists were reluctant to get rid of it, and still maintained it was a human ancestor. Dubois had also 'forgotten' to mention that he found the bones of modern humans at the same site.
Peking Man, made up from monkey skulls which were found in an ancient limestone burning industrial site where there were crushed monkey skulls and modern human bones. Drawings were made of Peking Man, but the original skull conveniently disappeared. So that allowed evolutionists to continue to use it as evidence without fear of it ever being debunked.
The Horse Series, unrelated species cobbled together, They were from different continents and were in no way a proper series of intermediates, They had different numbers of ribs etc. and the very first in the line, is similar to a creature alive today - the Hyrax.
Peppered Moth, moths were glued to trees to fake photographs for the peppered moth evidence. They don't normally rest on trees in daytime. In any case, the selection of a trait which is part of the variability of the existing gene pool, is not progressive evolution. It is just normal, natural selection within limits, which no-one disputes.
The Orgueil meteorite, organic material and even plant seeds were embedded and glued into the Orgueil meteorite and disguised with coal dust to make them look like part of the original meteorite, in a fraudulent attempt to fool the world into believing in the discredited idea of spontaneous generation of life, which is essential for progressive evolution to get started. The reasoning being that, if it could be shown that there was life in space, spontaneous generation must have happened there and could therefore be declared by evolutionists as being a scientific fact.
Is macro evolution even science? The answer to that has to be an emphatic - NO!
The usual definition of science is: that which can be demonstrated and observed and repeated. Evolution cannot be proved, or tested; it is claimed to have happened in the past, and, as such, it is not subject to the scientific method. It is merely a belief.
Of course, there is nothing wrong with having beliefs, especially if there is a wealth of evidence to support them, but they should not be presented as scientific fact. As we have shown, in the case of progressive evolution, there is a wealth of evidence against it. Nevertheless, we are told by evolutionist zealots that microbes to man evolution is a fact and likewise the spontaneous generation of life from sterile matter. They are deliberately misleading the public on both counts. Evolution is not only not a fact, it is not even proper science.
You don't need a degree in rocket science to understand that Darwinism has damaged and undermined science.
However, what does the world's, most famous, rocket scientist (the father of modern rocket science) have to say?
Wernher von Braun (1912 – 1977) PhD Aerospace Engineering
"In recent years, there has been a disturbing trend toward scientific dogmatism in some areas of science. Pronouncements by notable scientists and scientific organizations about "only one scientifically acceptable explanation" for events which are clearly outside the domain of science -- like all origins are -- can only destroy the curiosity of those who must carry on the future work of science. Humility, a seemingly natural product of studying nature, appears to have largely disappeared -- at least its visibility is clouded from the public's viewpoint.
Extrapolation backward in time until there are no physical artifacts of certainty that can be examined, requires sophisticated guessing which scientists prefer to refer to as "inference." Since hypotheses, a product of scientific inference, are virtually the stuff that comprises the cutting edge of scientific progress, inference must constantly be nurtured. However, the enthusiasm that encourages inference must be matched in degree with caution that clearly differentiates inference from what the public so readily accepts as "scientific fact." Failure to keep these two factors in balance can lead either to a sterile or a seduced science. 'Science but not Scientists' (2006) p.xi"
And the eminent scientist, William Robin Thompson (1887 - 1972) Entomologist and Director of the Commonwealth Institute of Biological Control, Ottawa, Canada, who was asked to write the introduction of the centenary edition of Darwin's 'Origin', wrote:
"The concept of organic Evolution is very highly prized by biologists, for many of whom it is an object of genuinely religious devotion, because they regard it as a supreme integrative principle. This is probably the reason why the severe methodological criticism employed in other departments of biology has not yet been brought to bear against evolutionary speculation." 'Science and Common Sense' (1937) p.229
“As we know, there is a great divergence of opinion among biologists … because the evidence is unsatisfactory and does not permit any certain conclusion. It is therefore right and proper to draw the attention of the non-scientific public to the disagreements about evolution. But some recent remarks of evolutionists show that they think this unreasonable ......
This situation, where scientific men rally to the defence of a doctrine they are unable to define scientifically, much less demonstrate with scientific rigor, attempting to maintain its credit with the public by the suppression of criticism and the elimination of difficulties, is abnormal and unwise in science.”
Prof. W. R. Thompson, F.R.S., introduction to the 1956 edition of Darwin's 'Origin of the Species'
"When I was asked to write an introduction replacing the one prepared a quarter of a century ago by the distinguished Darwinian, Sir Anthony Keith [one of the "discoverers" of Piltdown Man], I felt extremely hesitant to accept the invitation . . I am not satisfied that Darwin proved his point or that his influence in scientific and public thinking has been beneficial. If arguments fail to resist analysis, consent should be withheld and a wholesale conversion due to unsound argument must be regarded as deplorable. He fell back on speculative arguments."
"He merely showed, on the basis of certain facts and assumptions, how this might have happened, and as he had convinced himself he was able to convince others."
"But the facts and interpretations on which Darwin relied have now ceased to convince."
"This general tendency to eliminate, by means of unverifiable speculations, the limits of the categories Nature presents to us is the inheritance of biology from The Origin of Species. To establish the continuity required by the theory, historical arguments are invoked, even though historical evidence is lacking. Thus are engendered those fragile towers of hypothesis based on hypothesis, where fact and fiction intermingle in an inextricable confusion."—*W.R. Thompson, "Introduction," to Everyman’s Library issue of Charles Darwin, Origin of Species (1958 edition).
"The evolution theory can by no means be regarded as an innocuous natural philosophy, but rather is a serious obstruction to biological research. It obstructs—as has been repeatedly shown—the attainment of consistent results, even from uniform experimental material. For everything must ultimately be forced to fit this theory. An exact biology cannot, therefore, be built up."—*H. Neilsson, Synthetische Artbildng, 1954, p. 11
Berkeley University law professor, Philip Johnson, makes the following points: “(1) Evolution is grounded not on scientific fact, but on a philosophical belief called naturalism; (2) the belief that a large body of empirical evidence supports evolution is an illusion; (3) evolution is itself a religion; and, (4) if evolution were a scientific hypothesis based on rigorous study of the evidence, it would have been abandoned long ago.”
To end with a more jocular quote, it has been said that:
"If Classical Darwinism is evolution by creeps and punctuated equilibrium is evolution by jerks, then neo Darwinism is evolution by freaks".
The real theory of everything
www.flickr.com/photos/truth-in-science/34295660211
www.flickr.com/photos/truth-in-science/39554035561/in/dat...
Eudocimus albus (Linnaeus, 1758) - American white ibis in Florida, USA. (March 2014)
Birds are small to large, warm-blooded, egg-laying, feathered, bipedal vertebrates capable of powered flight (although some are secondarily flightless). Many scientists characterize birds as dinosaurs, but this is consequence of the physical structure of evolutionary diagrams. Birds aren’t dinosaurs. They’re birds. The logic & rationale that some use to justify statements such as “birds are dinosaurs” is the same logic & rationale that results in saying “vertebrates are echinoderms”. Well, no one says the latter. No one should say the former, either.
However, birds are evolutionarily derived from theropod dinosaurs. Birds first appeared in the Triassic or Jurassic, depending on which avian paleontologist you ask. They inhabit a wide variety of terrestrial and surface marine environments, and exhibit considerable variation in behaviors and diets.
Classification: Animalia, Chordata, Vertebrata, Aves, Ciconiiformes, Threskiornithidae
Locality: southern shore of Sanibel Island, southwestern Florida, USA
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More info. at:
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All the photography, swimsuits, gold 45 revolver and 45surf logos, clothing designs, and lingerie are composed and designed in accordance with the golden ratio and divine proportion!
Dr. E’s Golden Ratio Principle: The golden ratio exalts beauty because the number is a characteristic of the mathematically and physically most efficient manners of growth and distribution, on both evolutionary and purely physical levels. The golden ratio ensures that the proportions and structure of that which came before provide the proportions and structure of that which comes after, thusly providing symmetry over not only space but time, and exalting life’s foundational dynamic symmetry. Robust, ordered, symmetric growth is naturally associated with health and beauty, and thus we evolved to perceive the golden ratio harmonies as inherently beautiful, as we saw and felt their presence in all vital growth and life. In the salient features and proportions of humans and nature alike, from the distribution of our facial features and bones to the arrangements of petals, leaves, and sunflowers seeds. As ratios between Fibonacci Numbers offer the closest whole-number approximations to the golden ratio, and as seeds, cells, leaves, bones, and other physical entities appear in whole numbers, the Fibonacci Numbers oft appear in the arrangement of nature’s discrete elements as “growth’s numbers.” From the dawn of time, humanity sought to salute their gods in art and temples exalting the same proportion by which they and all their vital sustenance, as well as all the flowers and nature’s epic beauty, had been created—the golden ratio.
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Light Time Dimension Theory's dx4/dt=ic graces all the clothes, swimsuits, and lingerie!
Proof of Light Time Dimension Theory's principle of a fourth expanding dimension:
Proof of ltd’s principle:
1. The velocity of every object through
Spacetime is c.
2. The velocity of light through the
Three spatial dimensions is always c.
3. If light had any velocity through x4,
Light’s total velocity would not be c.
4. Ergo light remains stationary in x4.
5. Thus light tracks and traces the
Movement and character of x4.
6. As light is a spherically-symmetric,
Probabilistic wavefront expanding
At c, x4 expands at the rate of c in a
Spherically-symmetric manner,
Distributing nonlocality.
QED
Abstract
To understand the evolutionary significance of geographic variation, one must identify the factors that generate phenotypic differences among populations. I examined the causes of geographic variation in and evolutionary history of number of trunk vertebrae in slender salamanders. Batrachoseps (Caudata: Plethodontidae). Number of trunk vertebrae varies at many taxonomic levels within Batrachoseps. Parallel clines in number occur along an environmental gradient in three lineages in the Coast Ranges of California. These parallel clines may signal either adaptation or a shared phenotypically plastic response to the environmental gradient. By raising eggs from 10 populations representing four species of Batrachoseps, I demonstrated that number of trunk vertebrae can be altered by the developmental temperature; however, the degree of plasticity is insufficient to account for geographic variation. Thus, the geographic variation results largely from genetic variation. Number of trunk vertebrae covaries with body size and shape in diverse vertebrate taxa, including Batrachoseps. I hypothesize that selection for different degrees of elongation, possibly related to fossoriality, has led to the extensive evolution of number of trunk vertebrae in Batrachoseps. Analysis of intrapopulational variation revealed sexual dimorphism in both body shape and number of trunk vertebrae, but no correlation between these variables in either sex. Females are more elongate than males, a pattern that has been attributed to fecundity selection in other taxa. Patterns of covariation among different classes of vertebrae suggest that some intrapopulational variation in number results from changes in vertebral identity rather than changes in segmentation.
Elizabeth L. Jockusch
Evolution
Images in this gallery were captured by:
Mark Smith M.S. Geoscientist mark@macroscopicsolutions.com
Daniel Saftner B.S. Geoscientist and Returned Peace Corps Volunteer daniel@macroscopicsolutions.com
Annette Evans Ph.D. Student at the University of Connecticut annette@macroscopicsolutions.com
+++ DISCLAIMER +++
Nothing you see here is real, even though the conversion or the presented background story might be based historical facts. BEWARE!
Some background:
The Hawker Cyclone was an evolutionary successor to the successful Hawker Typhoon and Tempest fighters and fighter-bombers of the Second World War. The Cyclone's design process was initiated in September 1942 by Sydney Camm, one of Hawker's foremost aircraft designers, to meet the Royal Air Force’s requirement for a lightweight Tempest Mk.II and V replacement.
The project, tentatively designated Tempest Mk. VIII, was formalised in January 1943 when the Air Ministry issued Specification F.2/42 around the "Tempest Light Fighter".This was followed up by Specification F.2/43, issued in May 1943, which required a high rate of climb of not less than 4,500 ft/min (23 m/s) from ground level to 20,000 feet (6,096 m), good fighting manoeu rability and a maximum speed of at least 450 mph (724 km/h) at 22,000 feet (6,705 m). The armament was to be four 20mm Hispano V cannon with a total capacity of 600 rounds, plus the capability of carrying two bombs each up to 1,000 pounds (454 kg). In April 1943, Hawker had also received Specification N.7/43 from the Admiralty, who sought a navalized version of the developing aircraft, what eventually led to the Hawker Sea Fury, which was a completely new aircraft, which only shared the general outlines of the Tempest.
The Royal Air Force was looking for a quicker solution, and Camm started working on a new laminar flow wing, which would further improve the Tempest’s speed. Further refinements were done to other aerodynamic components, too, like the radiator, since the Tempest V’s liquid-cooled Napier Sabre engine was to be used. After some experiments with new arrangements, an annular radiator directly behind the propeller was chosen – certainly inspired by fast German aircraft like the Fw 190D and developed by Napier.
A total of three prototypes were ordered; the first one was powered by a Napier Sabre IIA liquid-cooled H-24 sleeve-valve engine, generating 2,180 hp (1,625 kW), but the second and any following aircraft carried the more powerful Sabre V with 2,340 hp, driving a Rotol four-blade propeller. Later aircraft were even to carry the Napier Sabre VII, which was capable of developing 3,400–4,000 hp (2,535–2,983 kW) and pushing the top speed to 485 mph (780 km/h) and more. The third airframe was just a static test structure. However, since the differences between the Tempest and the new aircraft had become almost as big as to its predecessor, the Typhoon, the new type received its own name Cyclone.
The first Cyclone Mk. I to fly, on 30 August 1944, was NV950, and it became clear soon that the modifications would improve the Cyclone’s top speed vs. the Tempest by almost 30 mph (50 km/h), but the new components would also require a longer testing period than expected. The annular radiator frequently failed and overheated, and the new, slender wings caused directional stability problems so that the complete tail section had to be re-designed. This troubling phase took more than 6 months, so that eventual service aircraft would only be ready in mid-1945 – too late for any serious impact in the conflict.
However, since the Hawker Fury, the land-based variant of the Sea Fury, which had been developed from the Tempest for the Royal Navy in parallel, had been cancelled, the Royal Air Force still ordered 150 Cyclone fighters (F Mk. I), of which one third would also carry cameras and other reconnaissance equipment (as Cyclone FR Mk.II). Due to the end of hostilities in late 1945, this order immediately lost priority. Consequently, the first production Cyclone fighters were delivered in summer 1946 – and in the meantime, jet fighters had rendered the piston-powered fighters obsolete, at least in RAF service. As a consequence, all Cyclones were handed over to friendly Commonwealth nations and their nascent air forces, e. g. India, Thailand or Burma. India received its first Cyclones in late 1947, just when the Kashmir conflict with Pakistan entered a hot phase. The machines became quickly involved in this conflict from early 1948 onwards.
Cyclones played an important role in the strikes against hostiles at Pir Badesar and the dominating Pir Kalewa. The taking of Ramgarh fort and Pt. 6944 on the west flank of Bhimbar Gali was to be a classic close support action with Indian forces carrying out a final bayonet charge against the enemy trenches whilst RIAF Cyclones and Tempests strafed and rocketed the trenches at close quarters. On a chance reconnaissance, enemy airfields were located at Gilgit and 40 NMs south, at Chilas. Cyclones flew several strikes against the landing strips in Oct and Nov 48, cratering & damaging both and destroying several hangars, barracks and radio installations. This attack destroyed Pakistani plans to build an offensive air capability in the North. Already, with Tempests and Cyclones prowling the valleys, Pakistani re-supply by Dakotas had been limited to hazardous night flying through the valleys.
After the end of hostilities in late 1948 and the ensuing independence, the Cyclone squadrons settled into their peace time stations. However, constant engine troubles (particularly the radiator) continued to claim aircraft and lives and the skill required to land the Cyclone because of its high approach speed continued to cause several write offs. The arrival of the jet-engined Vampire were the first signs of the Cyclone’s demise. As the IAF began a rapid expansion to an all jet force, several Tempest and Cyclone squadrons began converting to Vampires, 7 Squadron being the first in Dec 49. By this time it had already been decided that the piston-engine fighters would be relegated to the fighter lead-in role to train pilots for the new jet fighters. A conversion training flight was set up at Ambala in Sep 49 with Spitfire T Mk IXs, XVIIIs and Tempests to provide 16 hrs/six weeks of supervised Tempest training. This unit eventually moved to Hakimpet two years later and operated till the end of 1952. Some Cyclone FR Mk. IIs remained in front line service until 1954, though.
General characteristics:
Crew: One
Length: 35 ft 5 3/4 in (10.83 m)
Wingspan: 42 ft 5 1/2 in (12.96 m)
Height (tail down): 15 ft 6 3/4 in (4.75 m)
Wing area: 302 ft² (28 m²)
Empty weight: 9,250 lb (4,195 kg)
Loaded weight: 11,400 lb (5,176 kg)
Max. takeoff weight: 13,640 lb (6,190 kg)
Powerplant:
1× Napier Sabre V liquid-cooled H-24 sleeve-valve engine with 2,340 hp (1,683 kW)
Performance:
Maximum speed: 460 mph (740 km/h) 18,400 ft (5,608 m),
Range: 740 mi (1,190 km)
1,530 mi (2,462 km) with two 90 gal (409 l) drop tanks
Service ceiling: 36,500 ft (11,125 m)
Rate of climb: 4,700 ft/min (23.9 m/s)
Wing loading: 37.75 lb/ft² (184.86 kg/m²)
Power/mass: 0.21 hp/lb (0.31 kW/kg)
Armament:
4× 20 mm (.79 in) Mark V Hispano cannons, 200 RPG
2× underwing hardpoints for 500 lb (227 kg) or 1,000 lb (454 kg) bombs
or 2 × 45 gal (205 l) or 2 × 90 gal (409 l) drop tanks
plus 6× 3” (76.2 mm) RP-3 rockets
The kit and its assembly:
Another episode in the series “Things to make and do with Supermarine Attacker wings”. And what started as a simple switch of wings eventually turned into a major kitbashing, since the model evolved from a modded Tempest into something more complex and conclusive.
The initial spark was the idea of a Hawker alternative to Supermarine’s Spiteful and Seafang developments – especially with their slender laminar flow wings. Wouldn’t a Hawker alternative make sense?
Said and done, I dug out a NOVO Attacker kit and a Matchbox Tempest, and started measuring – and the wing transplantation appeared feasible! I made the cut on the Tempest wing just outside of the oil cooler, and the Attacker wings were then attached to these stubs – after some gaps for the landing gear wells had been cut into the massive lower wing halves. The stunt went more smoothly than expected, the only cosmetic flaw is that the guns went pretty far outboard, but that’s negligible.
But the different wings were not enough. I had recently seen in a book a picture of a Tempest (NV 768) with an experimental annular radiator for the Sabre engine (looking like a streamlined Tempest II), and wondered if this arrangement would have been the aerodynamically more efficient solution than the bulbous chin radiator of the Tempest V and VI? I decided to integrate this feature into my build, too, even though not as a copy of the real-world arrangement. The whole nose section, even though based on the OOB Mk. V nose, was scratched and re-sculpted with lots of putty. The radiator intake comes from a FROG He 219, with the front end opened and a fan from a Matchbox Fw 190 placed inside, as well as a styrene tube for the new propeller. The latter was scratched, too, from a Matchbox He 70 spinner and single blades from an Italeri F4U, plus a metal axis. The exhaust stubs were taken OOB, but their attachment slits had to be re-engraved into the new and almost massive nose section.
Once the wings and the nose became more concrete, I found that the Tempest’s original rounded tail surfaces would not match with the new, square wings. Therefore I replaced the stabilizers with donations from a Heller F-84G and modified the fin with a new, square tip (from an Intech Fw 190D) and got rid of the fin fillet – both just small modifications, but they change the Tempest’s profile thoroughly.
In order to underline the aircraft’s new, sleek lines, I left away any ordnance – but instead I added some camera fairings: one under the rear fuselage or a pair of vertical/oblique cameras, and another camera window portside for a horizontal camera. The openings were drilled, and, after painting, the kit the camera windows were created with Humbrol Clearfix.
Painting and markings:
Somehow I thought that this aircraft had to carry Indian markings – and I had a set of standard Chakra Wheels from the late Forties period in my stash. The camouflage is, typical for early IAF machines of British origin, RAF standard, with Dark Green and Ocean Grey from above and Medium Sea Grey from below. I just used the more brownish pst-war RAF Dark Green tone (Humbrol 163), coupled with the rather light Ocean Grey from Modelmaster (2057). The underside became Humbrol 165. All interior surfaces were painted with RAF Interior Green, nothing fancy. The only colorful addition is the saffron-colored spinner, in an attempt to match the fin flash’s tone.
As a standard measure, the kit received a black ink wash and some panel post-shading with lighter tones – only subtly, since the machine was not to look too weathered and beaten, just used from its Kashmir involvements.
The national markings come from a Printscale Airspeed Oxford sheet, the tactical code with alternating white and black letters, depending on the underground (the sky fuselage band comes from a Matchbox Brewster Buffalo), was puzzled together from single letters from TL Modellbau – both seen on different contemporary RIAF aircraft.
As another, small individual detail I gave the machine a tactical code letter on the fuselage, and the small tiger emblems under the cockpit were home-printed from the official IAF No. 1 Squadron badge.
Despite the massive modifications this one is a relatively subtle result, all the changes become only visible at a second glance. A sleek aircraft, and from certain angley the Cyclone looks like an A-1 Skyraider on a diet?
+++ DISCLAIMER +++
Nothing you see here is real, even though the conversion or the presented background story might be based on historical facts. BEWARE!
Some background:
When Marcel Dassault started work on jet-powered fighters after WWII, the development evolved in gradual steps instead of quantum leaps, leading to a long line of aircraft. The Mystère IV was an evolutionary development of the Mystère II aircraft. Although bearing an external resemblance to the earlier aircraft, the Mystère IV was in fact a new design with aerodynamic improvements for supersonic flight. The prototype first flew on 28 September 1952, and the aircraft entered service in April 1953. The first 50 Mystere IVA production aircraft were powered by British Rolls-Royce Tay turbojets, while the remainder had the French-built Hispano-Suiza Verdon 350 version of that engine.
France was the main operator of the Mystère IV. In April 1953 the United States government and the United States Air Force placed an order for 223 aircraft to be operated by the French, and at the peak usage the Armée de l‘air operated 6 squadrons. Most of the aircraft were purchased under a United States Offshore Procurement contract and many were returned to US custody after they were retired. The Mystère IVs were used in the 1956 Suez Crisis and continued to remain in French service into the 1980s, even though they were quickly relegated into second line duties as more capable types like the Super Mystère SM2B or the Mirage III entered service.
Other international operators included Israel (using about sixty Mystère IVs in large-scale combat during the 1967 Six Day War), India (104 aircraft procured in 1957 and extensively used in the Indo-Pakistani War of 1965) and Ecuador.
The Fuerza Aérea Ecuatoriana (FAE, Ecuadorian Air Force) was officially created on October 27, 1920. However, like in many other countries, military flying activity already started before the formal date of birth of the Air Force. By 1939 the Ecuadorian Air Force was still limited to about 30 aircraft, though, and a staff of about 60, including 10 officers. Military aviation did not start in earnest until the early forties when an Ecuadorian mission to the United States resulted in the delivery of an assortment of aircraft for the Aviation school at Salinas: three Ryan PT-22 Recruits, six Curtiss-Wright CW-22 Falcons, six Fairchild PT-19A Cornells and three North American AT-6A Harvards arrived in March 1942, considerably boosting the capacity of the Escuela de Aviación at Salinas.
The 1950s and 1960s saw a further necessary buildup of the air force, gaining more units and aircraft, while efforts were made in enhancing the facilities at various airbases. In May 1961 the "First Air Zone" with its subordinate unit Ala de Transportes No.11 was founded. The "Second Air Zone" controlled the units in the southern half of Ecuador, Ala de Combate No.21 at Taura, Ala de Rescate No.22 at Guayaquil and Ala de Combate No.23 at Manta as well as the Escuela Superior Militar de Aviación "Cosme Rennella B." (ESMA) at Salinas.
It was at this time that the FAE was looking for a capable (yet affordable) jet fighter that would replace the vintage F-47 “Thunderbolt” piston engine fighters of American origin that had been operated since 1947 as well as the ageing fleet of Gloster Meteor jet fighters. After consulting various options, including the British Hawker Hunter and the American F-86 Sabre, Ecuador settled upon the French Mystère IV. A total of 32 aircraft were ordered in 1958 and delivered until early 1963 in two tranches, subsequently outfitting two combat squadrons.
The Ecuadorian aircraft resembled the early French Mystère IV standard and were powered by the British Rolls-Royce Tay 250. However, they differed in small details and incorporated some updates, leading to the individual designation Mystère IVE (for Ecuador). This included a modified instrumentation and a British Martin Baker ejection seat in the cockpit. On the outside, a fairing for a brake parachute at the fin’s base was the most obvious change, and there were small oval boundary layer fences on the wings’ leading edges that improved the aircraft’s handling. The front landing gear was slightly different, too, now outfitted with a mudguard.
To improve the aircraft’s capabilities in air-to-air combat, an American AN/APG-30 range-finding radar was fitted, mounted to the center of the air intake (under a slightly enlarged radome) and linked with the gyroscopic gunsight in the cockpit. It was effective at a range of up to 2.750 m, but only covered a narrow cone directly in front of the aircraft. Initially the aircraft were operated as pure fighters/interceptors, but soon they also took over ground attack and CAS missions with iron bombs and unguided missiles, even though the Mystère IV’s ordnance capacity was rather limited. But the aircraft had a good handling at low altitude and were a stable weapon platform, so that the pilots operated them with confidence.
In the early Seventies, Ecuador had plans to upgrade its Mystères with Pratt & Whitney J48-P-5 engines, a license-built version of the Rolls-Royce Tay from the USA and outfitted with an afterburner. With reheat the J48 delivered 8,750 lbf (38.9 kN) of thrust, but continuous dry thrust was only 6,350 lbf (28.2 kN), markedly less than the old Tay engine. The high fuel consumption with operating afterburner would have markedly limited the aircraft’s range, and this engine switch would have necessitated major modifications to the aircrafts’ tail section, so that the upgrade eventually did not come to fruition due the lack of funds and the rather limited and only temporary improvement in performance.
Nevertheless, in course of their career in Ecuador, the Mystères’ still underwent some modifications and modernizations. In the early Seventies an MLU program was carried out: the retractable pannier for unguided missiles was deleted in favor of an extra fuel tank and upgraded navigational and weapon avionics. The latter included wirings for IR-guided AIM-9B Sidewinder AAMs on the outer underwing pylons, what greatly improved the aircraft’s air-to-air capabilities. The original DEFA 552 guns were replaced with more modern DEFA 553s, which had a new feed system, a nitro-chrome plated steel barrel (which was longer than the 552’s and now protruded visibly from the openings), a forged drum casing, and improved electrical reliability. During this upgrade phase the machines also lost their original natural metal livery and they received a less conspicuous tactical NATO-style grey/green paint scheme with metallic-grey undersides.
In this form the Ecuadorean Mystère IVEs soldiered on well into the Eighties, with a very good reliability record. During their active career they even saw “hot” action on several occasions, for instance in a continuous border dispute with Peru, the so-called Paquisha War. This brief military clash over the control of three watch posts flared up in January 1981 and the Mystères became involved. The first incident was a dogfight with an A-37B of the Fuerza Aérea del Peru (FAP), launched from Guayaquil to intercept it – with no casualities, though. Several similar interception incidents happened until early February 1981, and the FAE Mystères also flew several CAS missions to repel the Peruvian Jungle Infantry and to support Ecuadorian ground forces. Despite their age, the aircrafts’ ruggedness and simplicity proved them to be reliable, and its high roll rate and good handling at low altitude made it a versatile platform that was still competitive, even though its rather sluggish acceleration turned out to be a serious weak spot, esp. in the country’s typical mountainous terrain. Its relatively low range with internal fuel only was another operational problem.
The Mystère IVEs were finally retired in 1988 and replaced by Mirage F.1C fighters from France and IAI Kfir C.7 fighter bombers from Israel.
General characteristics:
Crew: 1
Length: 12.89 m (42 ft 3 in)
Wingspan: 11.12 m (36 ft 6 in)
Height: 4.6 m (15 ft 1 in)
Wing area: 32.06 m² (345.1 sq ft)
Empty weight: 5,860 kg (12,919 lb)
Gross weight: 8,510 kg (18,761 lb)
Max takeoff weight: 9,500 kg (20,944 lb)
Powerplant:
1× Rolls-Royce Tay 250 centrifugal-flow turbojet engine with 34.32 kN (7,720 lbf) thrust
Performance:
Maximum speed: 1,110 km/h (690 mph, 600 kn) at sea level
Range: 915 km (569 mi, 494 nmi) with internal fuel only
2,280 km (1,420 mi; 1,230 nmi) with drop tanks
Service ceiling: 15,000 m (49,000 ft)
Rate of climb: 40 m/s (7,900 ft/min)
Armament:
2× 30 mm (1.18 in) DEFA 553 cannon with 150 rounds per gun
1,000 kg (2,200 lb) of payload on four underwing hardpoints, incl. bombs, rockets or drop tanks
The kit and its assembly:
A very simple project, and basically just an OOB kit in the colors of a fictional operator. The whole thing was inspired by the question: what could have been a predecessor of the Ecuadorean Mirage F.1s? Not an existential question that might pop up frequently, but I quickly decided that the Mystère IV would have been a good/plausible contender. I found this idea even more attractive when I considered a camouflage paint scheme for it, because you only get either French or Indian machines in a uniform NMF outfit or IDF Mystères in desert camouflage (either in brown/blue or the later sand/earth/green scheme).
The kit is the venerable Matchbox Mystère IVA, even though in its Revell re-boxing. It’s a very simple affair, with partly crude details like the landing gear or the dreaded “trenches” for engraved surface details, esp. on the wings. But it goes together quite well, and with some corrections and additions you get a decent model.
The kit was basically built OOB, I just added underwings pylons with some ordnance for a fighter bomber mission: a pair of drop tanks and two SNEB missile launcher pods (tanks leftover from a Sword F-94, IIRC, and the pods from a Matchbox G.91Y). A complete tub with a floor and with side consoles (origin is uncertain, though – maybe it came from an Xtrakit Supermarin Swift?) was fitted to the cockpit and the primitive OOB ejection seat was replaced with something more convincing, pimped with seatbelts (masking tape) and ejection trigger handles (thin wire).
The flaps were lowered for a more natural look, and I added small oval boundary layer fences from a BAe Hawk as a personal twist. The clumsy front wheel, originally molded onto the strut as a single piece, was replaced with something better. The main landing gear covers were replaced with thinner styrene sheet material (the OOB parts are VERY thick) and pieces from hollow steel needles were implanted into the respective fairings as gun barrels.
A thinner pitot, created from heated sprue material, was used instead of the rather massive OOB part. The ranging radar fairing in the intake was slightly enlarged with the help of white glue. And, finally, a piece of sprue was implanted into the fin’s base as a brake parachute fairing, reminiscent of the Polish Lim-6/7, license-produced MiG-17s.
Painting and markings:
Actually quite conservative, with a typical Seventies paint scheme in dark grey/dark green. I even considered a more exotic three-tone scheme but found that – together with the colorful national markings – this would look too busy. Since there is no reference for a Mystère IV in such a guise, I simply adapted the standard pattern from a Royal Air Force Supermarine Swift. For a different look than the standard RAF colors – after all, the fictional Ecuadorean Mystère IVs were painted with domestic material. I used Humbrol 75 (Bronze Green) and ModelMaster 2057 (FS 36173, USAF Neutral Grey) for a good contrast between the upper tones, with Humbrol 56 (Alu Dope) underneath.
The tail section received a burned metal look, using Revell 91 (Iron) and some graphite. The cockpit interior was painted in a very dark grey (Revell 09, Anthracite) while the landing gear became silver-grey and the wells zinc-chromate primer (Humbrol 81). For some contrast, the drop tanks became shiny aluminum (Revell 99).
The kit received a light black ink washing, primarily for the recessed panel lines, and a subtle panel post-shading – for a less uniform surface than for true weathering, I’d imagine that the aircraft would be looked after well. However, some gun soot stains around the weapon ports were added with graphite, too.
The Ecuadorean roundels and unit markings came from an Xtradecal Strikemaster sheet, the tactical codes from a Croco Decal sheet for various South-American trainers. The flag on the rudder was, due to its sweep, painted, and most stencils were taken from the Mystère’s OOB sheet or procured from an Ecuadorian Mirage V on a Carpena sheet.
Finally, the kit was sealed with matt acrylic varnish, the ordnance was added and the position lights on the wing tips were created with silver and clear paint on top of that.
Well, this was not a spectacular conversion build, rather an OOB travesty with some cosmetic changes. However, the rather classic grey/green camouflage suits the tubby aircraft well and the bright national insignia really stand out on it – a pretty combo. The whole package as fictional Mystère IVE looks surprisingly convincing!
Konrad Lorenz, (born Nov. 7, 1903, Vienna, Austria—died Feb. 27, 1989, Altenburg), Austrian zoologist, founder of modern ethology, the study of animal behaviour by means of comparative zoological methods. His ideas contributed to an understanding of how behavioral patterns may be traced to an evolutionary past, and he was also known for his work on the roots of aggression. He shared the Nobel Prize for Physiology or Medicine in 1973 with the animal behaviourists Karl von Frisch and Nikolaas Tinbergen.
Lorenz was the son of an orthopedic surgeon. He showed an interest in animals at an early age, and he kept animals of various species—fish, birds, monkeys, dogs, cats, and rabbits—many of which he brought home from his boyhood excursions. While still young, he provided nursing care for sick animals from the nearby Schönbrunner Zoo. He also kept detailed records of bird behaviour in the form of diaries.
In 1922, after graduating from secondary school, he followed his father’s wishes that he study medicine and spent two semesters at Columbia University, in New York City. He then returned to Vienna to study.
During his medical studies Lorenz continued to make detailed observations of animal behaviour; a diary about a jackdaw that he kept was published in 1927 in the prestigious Journal für Ornithologie. He received an M.D. degree at the University of Vienna in 1928 and was awarded a Ph.D. in zoology in 1933. Encouraged by the positive response to his scientific work, Lorenz established colonies of birds, such as the jackdaw and greylag goose, published a series of research papers on his observations of them, and soon gained an international reputation.
In 1935 Lorenz described learning behaviour in young ducklings and goslings. He observed that at a certain critical stage soon after hatching, they learn to follow real or foster parents. The process, which is called imprinting, involves visual and auditory stimuli from the parent object; these elicit a following response in the young that affects their subsequent adult behaviour. Lorenz demonstrated the phenomenon by appearing before newly hatched mallard ducklings and imitating a mother duck’s quacking sounds, upon which the young birds regarded him as their mother and followed him accordingly.
In 1936 the German Society for Animal Psychology was founded. The following year Lorenz became coeditor in chief of the new Zeitschrift für Tierpsychologie, which became a leading journal for ethology. Also in 1937, he was appointed lecturer in comparative anatomy and animal psychology at the University of Vienna. From 1940 to 1942 he was professor and head of the department of general psychology at the Albertus University at Königsberg, Germany (now Kaliningrad, Russia).
From 1942 to 1944 he served as a physician in the German army and was captured as a prisoner of war in the Soviet Union. He was returned to Austria in 1948 and headed the Institute of Comparative Ethology at Altenberg from 1949 to 1951. In 1950 he established a comparative ethology department in the Max Planck Institute of Buldern, Westphalia, becoming codirector of the Institute in 1954. From 1961 to 1973 he served as director of the Max Planck Institute for Behaviour Physiology, in Seewiesen. In 1973 Lorenz, together with Frisch and Tinbergen, was awarded the Nobel Prize for Physiology or Medicine for their discoveries concerning animal behavioral patterns. In the same year, Lorenz became director of the department of animal sociology at the Institute for Comparative Ethology of the Austrian Academy of Sciences in Altenberg.
Lorenz’s early scientific contributions dealt with the nature of instinctive behavioral acts, particularly how such acts come about and the source of nervous energy for their performance. He also investigated how behaviour may result from two or more basic drives that are activated simultaneously in an animal. Working with Nikolaas Tinbergen of the Netherlands, Lorenz showed that different forms of behaviour are harmonized in a single action sequence.
Lorenz’s concepts advanced the modern scientific understanding of how behavioral patterns evolve in a species, particularly with respect to the role played by ecological factors and the adaptive value of behaviour for species survival. He proposed that animal species are genetically constructed so as to learn specific kinds of information that are important for the survival of the species. His ideas have also cast light on how behavioral patterns develop and mature during the life of an individual organism.
In the latter part of his career, Lorenz applied his ideas to the behaviour of humans as members of a social species, an application with controversial philosophical and sociological implications. In a popular book, Das sogenannte Böse (1963; On Aggression), he argued that fighting and warlike behaviour in man have an inborn basis but can be environmentally modified by the proper understanding and provision for the basic instinctual needs of human beings. Fighting in lower animals has a positive survival function, he observed, such as the dispersion of competitors and the maintenance of territory. Warlike tendencies in humans may likewise be ritualized into socially useful behaviour patterns. In another work, Die Rückseite des Spiegels: Versuch einer Naturgeschichte menschlichen Erkennens (1973; Behind the Mirror: A Search for a Natural History of Human Knowledge), Lorenz examined the nature of human thought and intelligence and attributed the problems of modern civilization largely to the limitations his study revealed.
Eckhard H. Hess
The Manchester Museum, Oxford Road, Manchester, Greater Manchester.
The museum's first collections were assembled by the Manchester Society of Natural History formed in 1821 with the purchase of the collection of John Leigh Philips. In 1850 the collections of the Manchester Geological Society were added. By the 1860s both societies encountered financial difficulties and, on the advice of the evolutionary biologist Thomas Huxley, Owens College (now the University of Manchester) accepted responsibility for the collections in 1867. The museum in Peter Street was sold in 1875 after Owens College moved to new buildings in Oxford Street.
The college commissioned Alfred Waterhouse, architect of London's Natural History Museum, to design a museum to house the collections for the benefit of students and the public on a site in Oxford Road (then Oxford Street). The Manchester Museum was opened to the public in 1888. At the time, the scientific departments of the college were immediately adjacent, and students entered the galleries from their teaching rooms in the Beyer Building.
Two subsequent extensions mirror the development of its collections. The 1912 pavilion was largely funded by Jesse Haworth, a textile merchant, to house the archaeological and Egyptological collections acquired through excavations he had supported. The 1927 extension was built to house the ethnographic collections. The Gothic Revival street frontage which continues to the Whitworth Hall has been ingeniously integrated by three generations of the Waterhouse family. When the adjacent University Dental Hospital of Manchester moved to a new site, its old building was used for teaching and subsequently occupied by the museum.
The museum is one of the University of Manchester's 'cultural assets', along with the Whitworth Art Gallery, John Rylands Library, Jodrell Bank visitor centre and others.
Information Source:
The cat (Felis catus), commonly referred to as the domestic cat or house cat, is the only domesticated species in the family Felidae. Recent advances in archaeology and genetics have shown that the domestication of the cat occurred in the Near East around 7500 BC. It is commonly kept as a house pet and farm cat, but also ranges freely as a feral cat avoiding human contact. It is valued by humans for companionship and its ability to kill vermin. Because of its retractable claws it is adapted to killing small prey like mice and rats. It has a strong flexible body, quick reflexes, sharp teeth, and its night vision and sense of smell are well developed. It is a social species, but a solitary hunter and a crepuscular predator. Cat communication includes vocalizations like meowing, purring, trilling, hissing, growling, and grunting as well as cat body language. It can hear sounds too faint or too high in frequency for human ears, such as those made by small mammals. It also secretes and perceives pheromones.
Female domestic cats can have kittens from spring to late autumn in temperate zones and throughout the year in equatorial regions, with litter sizes often ranging from two to five kittens. Domestic cats are bred and shown at events as registered pedigreed cats, a hobby known as cat fancy. Animal population control of cats may be achieved by spaying and neutering, but their proliferation and the abandonment of pets has resulted in large numbers of feral cats worldwide, contributing to the extinction of bird, mammal and reptile species.
As of 2017, the domestic cat was the second most popular pet in the United States, with 95.6 million cats owned and around 42 million households owning at least one cat. In the United Kingdom, 26% of adults have a cat, with an estimated population of 10.9 million pet cats as of 2020. As of 2021, there were an estimated 220 million owned and 480 million stray cats in the world.
Etymology and naming
The origin of the English word cat, Old English catt, is thought to be the Late Latin word cattus, which was first used at the beginning of the 6th century. The Late Latin word may be derived from an unidentified African language. The Nubian word kaddîska 'wildcat' and Nobiin kadīs are possible sources or cognates. The Nubian word may be a loan from Arabic قَطّ qaṭṭ ~ قِطّ qiṭṭ.
The forms might also have derived from an ancient Germanic word that was imported into Latin and then into Greek, Syriac, and Arabic. The word may be derived from Germanic and Northern European languages, and ultimately be borrowed from Uralic, cf. Northern Sámi gáđfi, 'female stoat', and Hungarian hölgy, 'lady, female stoat'; from Proto-Uralic *käďwä, 'female (of a furred animal)'.
The English puss, extended as pussy and pussycat, is attested from the 16th century and may have been introduced from Dutch poes or from Low German puuskatte, related to Swedish kattepus, or Norwegian pus, pusekatt. Similar forms exist in Lithuanian puižė and Irish puisín or puiscín. The etymology of this word is unknown, but it may have arisen from a sound used to attract a cat.
A male cat is called a tom or tomcat (or a gib, if neutered). A female is called a queen or a molly, if spayed, especially in a cat-breeding context. A juvenile cat is referred to as a kitten. In Early Modern English, the word kitten was interchangeable with the now-obsolete word catling.
A group of cats can be referred to as a clowder or a glaring.
Taxonomy
The scientific name Felis catus was proposed by Carl Linnaeus in 1758 for a domestic cat. Felis catus domesticus was proposed by Johann Christian Polycarp Erxleben in 1777. Felis daemon proposed by Konstantin Satunin in 1904 was a black cat from the Transcaucasus, later identified as a domestic cat.
In 2003, the International Commission on Zoological Nomenclature ruled that the domestic cat is a distinct species, namely Felis catus. In 2007, it was considered a subspecies, F. silvestris catus, of the European wildcat (F. silvestris) following results of phylogenetic research. In 2017, the IUCN Cat Classification Taskforce followed the recommendation of the ICZN in regarding the domestic cat as a distinct species, Felis catus.
Evolution
Main article: Cat evolution
The domestic cat is a member of the Felidae, a family that had a common ancestor about 10 to 15 million years ago. The evolutionary radiation of the Felidae began in Asia during the Miocene around 8.38 to 14.45 million years ago. Analysis of mitochondrial DNA of all Felidae species indicates a radiation at 6.46 to 16.76 million years ago. The genus Felis genetically diverged from other Felidae around 6 to 7 million years ago. Results of phylogenetic research shows that the wild members of this genus evolved through sympatric or parapatric speciation, whereas the domestic cat evolved through artificial selection. The domestic cat and its closest wild ancestor are diploid and both possess 38 chromosomes and roughly 20,000 genes.
Domestication
See also: Domestication of the cat and Cats in ancient Egypt
It was long thought that the domestication of the cat began in ancient Egypt, where cats were venerated from around 3100 BC, However, the earliest known indication for the taming of an African wildcat was excavated close by a human Neolithic grave in Shillourokambos, southern Cyprus, dating to about 7500–7200 BC. Since there is no evidence of native mammalian fauna on Cyprus, the inhabitants of this Neolithic village most likely brought the cat and other wild mammals to the island from the Middle Eastern mainland. Scientists therefore assume that African wildcats were attracted to early human settlements in the Fertile Crescent by rodents, in particular the house mouse (Mus musculus), and were tamed by Neolithic farmers. This mutual relationship between early farmers and tamed cats lasted thousands of years. As agricultural practices spread, so did tame and domesticated cats. Wildcats of Egypt contributed to the maternal gene pool of the domestic cat at a later time.
The earliest known evidence for the occurrence of the domestic cat in Greece dates to around 1200 BC. Greek, Phoenician, Carthaginian and Etruscan traders introduced domestic cats to southern Europe. During the Roman Empire they were introduced to Corsica and Sardinia before the beginning of the 1st millennium. By the 5th century BC, they were familiar animals around settlements in Magna Graecia and Etruria. By the end of the Western Roman Empire in the 5th century, the Egyptian domestic cat lineage had arrived in a Baltic Sea port in northern Germany.
The leopard cat (Prionailurus bengalensis) was tamed independently in China around 5500 BC. This line of partially domesticated cats leaves no trace in the domestic cat populations of today.
During domestication, cats have undergone only minor changes in anatomy and behavior, and they are still capable of surviving in the wild. Several natural behaviors and characteristics of wildcats may have pre-adapted them for domestication as pets. These traits include their small size, social nature, obvious body language, love of play, and high intelligence. Captive Leopardus cats may also display affectionate behavior toward humans but were not domesticated. House cats often mate with feral cats. Hybridisation between domestic and other Felinae species is also possible, producing hybrids such as the Kellas cat in Scotland.
Development of cat breeds started in the mid 19th century. An analysis of the domestic cat genome revealed that the ancestral wildcat genome was significantly altered in the process of domestication, as specific mutations were selected to develop cat breeds. Most breeds are founded on random-bred domestic cats. Genetic diversity of these breeds varies between regions, and is lowest in purebred populations, which show more than 20 deleterious genetic disorders.
Characteristics
Main article: Cat anatomy
Size
The domestic cat has a smaller skull and shorter bones than the European wildcat. It averages about 46 cm (18 in) in head-to-body length and 23–25 cm (9.1–9.8 in) in height, with about 30 cm (12 in) long tails. Males are larger than females. Adult domestic cats typically weigh 4–5 kg (8.8–11.0 lb).
Skeleton
Cats have seven cervical vertebrae (as do most mammals); 13 thoracic vertebrae (humans have 12); seven lumbar vertebrae (humans have five); three sacral vertebrae (as do most mammals, but humans have five); and a variable number of caudal vertebrae in the tail (humans have only three to five vestigial caudal vertebrae, fused into an internal coccyx). The extra lumbar and thoracic vertebrae account for the cat's spinal mobility and flexibility. Attached to the spine are 13 ribs, the shoulder, and the pelvis. Unlike human arms, cat forelimbs are attached to the shoulder by free-floating clavicle bones which allow them to pass their body through any space into which they can fit their head.
Skull
The cat skull is unusual among mammals in having very large eye sockets and a powerful specialized jaw. Within the jaw, cats have teeth adapted for killing prey and tearing meat. When it overpowers its prey, a cat delivers a lethal neck bite with its two long canine teeth, inserting them between two of the prey's vertebrae and severing its spinal cord, causing irreversible paralysis and death. Compared to other felines, domestic cats have narrowly spaced canine teeth relative to the size of their jaw, which is an adaptation to their preferred prey of small rodents, which have small vertebrae.
The premolar and first molar together compose the carnassial pair on each side of the mouth, which efficiently shears meat into small pieces, like a pair of scissors. These are vital in feeding, since cats' small molars cannot chew food effectively, and cats are largely incapable of mastication.: Cats tend to have better teeth than most humans, with decay generally less likely because of a thicker protective layer of enamel, a less damaging saliva, less retention of food particles between teeth, and a diet mostly devoid of sugar. Nonetheless, they are subject to occasional tooth loss and infection.
Claws
Cats have protractible and retractable claws. In their normal, relaxed position, the claws are sheathed with the skin and fur around the paw's toe pads. This keeps the claws sharp by preventing wear from contact with the ground and allows for the silent stalking of prey. The claws on the forefeet are typically sharper than those on the hindfeet. Cats can voluntarily extend their claws on one or more paws. They may extend their claws in hunting or self-defense, climbing, kneading, or for extra traction on soft surfaces. Cats shed the outside layer of their claw sheaths when scratching rough surfaces.
Most cats have five claws on their front paws and four on their rear paws. The dewclaw is proximal to the other claws. More proximally is a protrusion which appears to be a sixth "finger". This special feature of the front paws on the inside of the wrists has no function in normal walking but is thought to be an antiskidding device used while jumping. Some cat breeds are prone to having extra digits ("polydactyly"). Polydactylous cats occur along North America's northeast coast and in Great Britain.
Ambulation
The cat is digitigrade. It walks on the toes, with the bones of the feet making up the lower part of the visible leg. Unlike most mammals, it uses a "pacing" gait and moves both legs on one side of the body before the legs on the other side. It registers directly by placing each hind paw close to the track of the corresponding fore paw, minimizing noise and visible tracks. This also provides sure footing for hind paws when navigating rough terrain. As it speeds up from walking to trotting, its gait changes to a "diagonal" gait: The diagonally opposite hind and fore legs move simultaneously.
Balance
Cats are generally fond of sitting in high places or perching. A higher place may serve as a concealed site from which to hunt; domestic cats strike prey by pouncing from a perch such as a tree branch. Another possible explanation is that height gives the cat a better observation point, allowing it to survey its territory. A cat falling from heights of up to 3 m (9.8 ft) can right itself and land on its paws.
During a fall from a high place, a cat reflexively twists its body and rights itself to land on its feet using its acute sense of balance and flexibility. This reflex is known as the cat righting reflex. A cat always rights itself in the same way during a fall, if it has enough time to do so, which is the case in falls of 90 cm (3.0 ft) or more. How cats are able to right themselves when falling has been investigated as the "falling cat problem".
Coats
Main article: Cat coat genetics
The cat family (Felidae) can pass down many colors and patterns to their offspring. The domestic cat genes MC1R and ASIP allow for the variety of color in coats. The feline ASIP gene consists of three coding exons. Three novel microsatellite markers linked to ASIP were isolated from a domestic cat BAC clone containing this gene and were used to perform linkage analysis in a pedigree of 89 domestic cats that segregated for melanism.[citation needed]
Senses
Main article: Cat senses
Vision
A cat's nictitating membrane shown as it blinks
Cats have excellent night vision and can see at only one-sixth the light level required for human vision. This is partly the result of cat eyes having a tapetum lucidum, which reflects any light that passes through the retina back into the eye, thereby increasing the eye's sensitivity to dim light. Large pupils are an adaptation to dim light. The domestic cat has slit pupils, which allow it to focus bright light without chromatic aberration. At low light, a cat's pupils expand to cover most of the exposed surface of its eyes. The domestic cat has rather poor color vision and only two types of cone cells, optimized for sensitivity to blue and yellowish green; its ability to distinguish between red and green is limited. A response to middle wavelengths from a system other than the rod cells might be due to a third type of cone. This appears to be an adaptation to low light levels rather than representing true trichromatic vision. Cats also have a nictitating membrane, allowing them to blink without hindering their vision.
Hearing
The domestic cat's hearing is most acute in the range of 500 Hz to 32 kHz. It can detect an extremely broad range of frequencies ranging from 55 Hz to 79 kHz, whereas humans can only detect frequencies between 20 Hz and 20 kHz. It can hear a range of 10.5 octaves, while humans and dogs can hear ranges of about 9 octaves. Its hearing sensitivity is enhanced by its large movable outer ears, the pinnae, which amplify sounds and help detect the location of a noise. It can detect ultrasound, which enables it to detect ultrasonic calls made by rodent prey. Recent research has shown that cats have socio-spatial cognitive abilities to create mental maps of owners' locations based on hearing owners' voices.
Smell
Cats have an acute sense of smell, due in part to their well-developed olfactory bulb and a large surface of olfactory mucosa, about 5.8 cm2 (0.90 in2) in area, which is about twice that of humans. Cats and many other animals have a Jacobson's organ in their mouths that is used in the behavioral process of flehmening. It allows them to sense certain aromas in a way that humans cannot. Cats are sensitive to pheromones such as 3-mercapto-3-methylbutan-1-ol, which they use to communicate through urine spraying and marking with scent glands. Many cats also respond strongly to plants that contain nepetalactone, especially catnip, as they can detect that substance at less than one part per billion. About 70–80% of cats are affected by nepetalactone. This response is also produced by other plants, such as silver vine (Actinidia polygama) and the herb valerian; it may be caused by the smell of these plants mimicking a pheromone and stimulating cats' social or sexual behaviors.
Taste
Cats have relatively few taste buds compared to humans (470 or so versus more than 9,000 on the human tongue). Domestic and wild cats share a taste receptor gene mutation that keeps their sweet taste buds from binding to sugary molecules, leaving them with no ability to taste sweetness. They, however, possess taste bud receptors specialized for acids, amino acids like protein, and bitter tastes. Their taste buds possess the receptors needed to detect umami. However, these receptors contain molecular changes that make the cat taste of umami different from that of humans. In humans, they detect the amino acids of glutamic acid and aspartic acid, but in cats they instead detect nucleotides, in this case inosine monophosphate and l-Histidine. These nucleotides are particularly enriched in tuna. This has been argued is why cats find tuna so palatable: as put by researchers into cat taste, "the specific combination of the high IMP and free l-Histidine contents of tuna" .. "produces a strong umami taste synergy that is highly preferred by cats". One of the researchers involved in this research has further claimed, "I think umami is as important for cats as sweet is for humans".[87]
Cats also have a distinct temperature preference for their food, preferring food with a temperature around 38 °C (100 °F) which is similar to that of a fresh kill; some cats reject cold food (which would signal to the cat that the "prey" item is long dead and therefore possibly toxic or decomposing).
Whiskers
To aid with navigation and sensation, cats have dozens of movable whiskers (vibrissae) over their body, especially their faces. These provide information on the width of gaps and on the location of objects in the dark, both by touching objects directly and by sensing air currents; they also trigger protective blink reflexes to protect the eyes from damage.: 47
Behavior
See also: Cat behavior
Outdoor cats are active both day and night, although they tend to be slightly more active at night.[88] Domestic cats spend the majority of their time in the vicinity of their homes but can range many hundreds of meters from this central point. They establish territories that vary considerably in size, in one study ranging 7–28 ha (17–69 acres). The timing of cats' activity is quite flexible and varied but being low-light predators, they are generally crepuscular, which means they tend to be more active near dawn and dusk. However, house cats' behavior is also influenced by human activity and they may adapt to their owners' sleeping patterns to some extent.
Cats conserve energy by sleeping more than most animals, especially as they grow older. The daily duration of sleep varies, usually between 12 and 16 hours, with 13 and 14 being the average. Some cats can sleep as much as 20 hours. The term "cat nap" for a short rest refers to the cat's tendency to fall asleep (lightly) for a brief period. While asleep, cats experience short periods of rapid eye movement sleep often accompanied by muscle twitches, which suggests they are dreaming.
Sociability
The social behavior of the domestic cat ranges from widely dispersed individuals to feral cat colonies that gather around a food source, based on groups of co-operating females. Within such groups, one cat is usually dominant over the others. Each cat in a colony holds a distinct territory, with sexually active males having the largest territories, which are about 10 times larger than those of female cats and may overlap with several females' territories. These territories are marked by urine spraying, by rubbing objects at head height with secretions from facial glands, and by defecation. Between these territories are neutral areas where cats watch and greet one another without territorial conflicts. Outside these neutral areas, territory holders usually chase away stranger cats, at first by staring, hissing, and growling and, if that does not work, by short but noisy and violent attacks. Despite this colonial organization, cats do not have a social survival strategy or a herd behavior, and always hunt alone.
Life in proximity to humans and other domestic animals has led to a symbiotic social adaptation in cats, and cats may express great affection toward humans or other animals. Ethologically, a cat's human keeper functions as if a mother surrogate. Adult cats live their lives in a kind of extended kittenhood, a form of behavioral neoteny. Their high-pitched sounds may mimic the cries of a hungry human infant, making them particularly difficult for humans to ignore. Some pet cats are poorly socialized. In particular, older cats show aggressiveness toward newly arrived kittens, which include biting and scratching; this type of behavior is known as feline asocial aggression.
Redirected aggression is a common form of aggression which can occur in multiple cat households. In redirected aggression there is usually something that agitates the cat: this could be a sight, sound, or another source of stimuli which causes a heightened level of anxiety or arousal. If the cat cannot attack the stimuli, it may direct anger elsewhere by attacking or directing aggression to the nearest cat, dog, human or other being.
Domestic cats' scent rubbing behavior toward humans or other cats is thought to be a feline means for social bonding.
Communication
Main article: Cat communication
Domestic cats use many vocalizations for communication, including purring, trilling, hissing, growling/snarling, grunting, and several different forms of meowing. Their body language, including position of ears and tail, relaxation of the whole body, and kneading of the paws, are all indicators of mood. The tail and ears are particularly important social signal mechanisms in cats. A raised tail indicates a friendly greeting, and flattened ears indicate hostility. Tail-raising also indicates the cat's position in the group's social hierarchy, with dominant individuals raising their tails less often than subordinate ones. Feral cats are generally silent.: 208 Nose-to-nose touching is also a common greeting and may be followed by social grooming, which is solicited by one of the cats raising and tilting its head.
Purring may have developed as an evolutionary advantage as a signaling mechanism of reassurance between mother cats and nursing kittens, who are thought to use it as a care-soliciting signal. Post-nursing cats also often purr as a sign of contentment: when being petted, becoming relaxed, or eating. Even though purring is popularly interpreted as indicative of pleasure, it has been recorded in a wide variety of circumstances, most of which involve physical contact between the cat and another, presumably trusted individual. Some cats have been observed to purr continuously when chronically ill or in apparent pain.
The exact mechanism by which cats purr has long been elusive, but it has been proposed that purring is generated via a series of sudden build-ups and releases of pressure as the glottis is opened and closed, which causes the vocal folds to separate forcefully. The laryngeal muscles in control of the glottis are thought to be driven by a neural oscillator which generates a cycle of contraction and release every 30–40 milliseconds (giving a frequency of 33 to 25 Hz).
Domestic cats observed in a rescue facility have total of 276 distinct facial expressions based on 26 different facial movements; each facial expression corresponds to different social functions that are likely influenced by domestication.
Grooming
Cats are known for spending considerable amounts of time licking their coats to keep them clean. The cat's tongue has backward-facing spines about 500 μm long, which are called papillae. These contain keratin which makes them rigid so the papillae act like a hairbrush. Some cats, particularly longhaired cats, occasionally regurgitate hairballs of fur that have collected in their stomachs from grooming. These clumps of fur are usually sausage-shaped and about 2–3 cm (0.79–1.18 in) long. Hairballs can be prevented with remedies that ease elimination of the hair through the gut, as well as regular grooming of the coat with a comb or stiff brush.
Fighting
Among domestic cats, males are more likely to fight than females. Among feral cats, the most common reason for cat fighting is competition between two males to mate with a female. In such cases, most fights are won by the heavier male. Another common reason for fighting in domestic cats is the difficulty of establishing territories within a small home. Female cats also fight over territory or to defend their kittens. Neutering will decrease or eliminate this behavior in many cases, suggesting that the behavior is linked to sex hormones.
When cats become aggressive, they try to make themselves appear larger and more threatening by raising their fur, arching their backs, turning sideways and hissing or spitting. Often, the ears are pointed down and back to avoid damage to the inner ear and potentially listen for any changes behind them while focused forward. Cats may also vocalize loudly and bare their teeth in an effort to further intimidate their opponents. Fights usually consist of grappling and delivering powerful slaps to the face and body with the forepaws as well as bites. Cats also throw themselves to the ground in a defensive posture to rake their opponent's belly with their powerful hind legs.
Serious damage is rare, as the fights are usually short in duration, with the loser running away with little more than a few scratches to the face and ears. Fights for mating rights are typically more severe and injuries may include deep puncture wounds and lacerations. Normally, serious injuries from fighting are limited to infections of scratches and bites, though these can occasionally kill cats if untreated. In addition, bites are probably the main route of transmission of feline immunodeficiency virus. Sexually active males are usually involved in many fights during their lives, and often have decidedly battered faces with obvious scars and cuts to their ears and nose. Cats are willing to threaten animals larger than them to defend their territory, such as dogs and foxes.
Hunting and feeding
See also: Cat food
The shape and structure of cats' cheeks is insufficient to allow them to take in liquids using suction. Therefore, when drinking they lap with the tongue to draw liquid upward into their mouths. Lapping at a rate of four times a second, the cat touches the smooth tip of its tongue to the surface of the water, and quickly retracts it like a corkscrew, drawing water upward.
Feral cats and free-fed house cats consume several small meals in a day. The frequency and size of meals varies between individuals. They select food based on its temperature, smell and texture; they dislike chilled foods and respond most strongly to moist foods rich in amino acids, which are similar to meat. Cats reject novel flavors (a response termed neophobia) and learn quickly to avoid foods that have tasted unpleasant in the past. It is also a common misconception that cats like milk/cream, as they tend to avoid sweet food and milk. Most adult cats are lactose intolerant; the sugar in milk is not easily digested and may cause soft stools or diarrhea. Some also develop odd eating habits and like to eat or chew on things like wool, plastic, cables, paper, string, aluminum foil, or even coal. This condition, pica, can threaten their health, depending on the amount and toxicity of the items eaten.
Cats hunt small prey, primarily birds and rodents, and are often used as a form of pest control. Other common small creatures such as lizards and snakes may also become prey. Cats use two hunting strategies, either stalking prey actively, or waiting in ambush until an animal comes close enough to be captured. The strategy used depends on the prey species in the area, with cats waiting in ambush outside burrows, but tending to actively stalk birds.: 153 Domestic cats are a major predator of wildlife in the United States, killing an estimated 1.3 to 4.0 billion birds and 6.3 to 22.3 billion mammals annually.
Certain species appear more susceptible than others; in one English village, for example, 30% of house sparrow mortality was linked to the domestic cat. In the recovery of ringed robins (Erithacus rubecula) and dunnocks (Prunella modularis) in Britain, 31% of deaths were a result of cat predation. In parts of North America, the presence of larger carnivores such as coyotes which prey on cats and other small predators reduces the effect of predation by cats and other small predators such as opossums and raccoons on bird numbers and variety.
Perhaps the best-known element of cats' hunting behavior, which is commonly misunderstood and often appalls cat owners because it looks like torture, is that cats often appear to "play" with prey by releasing and recapturing it. This cat and mouse behavior is due to an instinctive imperative to ensure that the prey is weak enough to be killed without endangering the cat.
Another poorly understood element of cat hunting behavior is the presentation of prey to human guardians. One explanation is that cats adopt humans into their social group and share excess kill with others in the group according to the dominance hierarchy, in which humans are reacted to as if they are at or near the top. Another explanation is that they attempt to teach their guardians to hunt or to help their human as if feeding "an elderly cat, or an inept kitten". This hypothesis is inconsistent with the fact that male cats also bring home prey, despite males having negligible involvement in raising kittens.:
Play
Main article: Cat play and toys
Domestic cats, especially young kittens, are known for their love of play. This behavior mimics hunting and is important in helping kittens learn to stalk, capture, and kill prey. Cats also engage in play fighting, with each other and with humans. This behavior may be a way for cats to practice the skills needed for real combat, and might also reduce any fear they associate with launching attacks on other animals.
Cats also tend to play with toys more when they are hungry. Owing to the close similarity between play and hunting, cats prefer to play with objects that resemble prey, such as small furry toys that move rapidly, but rapidly lose interest. They become habituated to a toy they have played with before. String is often used as a toy, but if it is eaten, it can become caught at the base of the cat's tongue and then move into the intestines, a medical emergency which can cause serious illness, even death. Owing to the risks posed by cats eating string, it is sometimes replaced with a laser pointer's dot, which cats may chase.
Reproduction
See also: Kitten
The cat secretes and perceives pheromones. Female cats, called queens, are polyestrous with several estrus cycles during a year, lasting usually 21 days. They are usually ready to mate between early February and August in northern temperate zones and throughout the year in equatorial regions.
Several males, called tomcats, are attracted to a female in heat. They fight over her, and the victor wins the right to mate. At first, the female rejects the male, but eventually, the female allows the male to mate. The female utters a loud yowl as the male pulls out of her because a male cat's penis has a band of about 120–150 backward-pointing penile spines, which are about 1 mm (0.039 in) long; upon withdrawal of the penis, the spines may provide the female with increased sexual stimulation, which acts to induce ovulation.
After mating, the female cleans her vulva thoroughly. If a male attempts to mate with her at this point, the female attacks him. After about 20 to 30 minutes, once the female is finished grooming, the cycle will repeat. Because ovulation is not always triggered by a single mating, females may not be impregnated by the first male with which they mate. Furthermore, cats are superfecund; that is, a female may mate with more than one male when she is in heat, with the result that different kittens in a litter may have different fathers.
The morula forms 124 hours after conception. At 148 hours, early blastocysts form. At 10–12 days, implantation occurs. The gestation of queens lasts between 64 and 67 days, with an average of 65 days.
Data on the reproductive capacity of more than 2,300 free-ranging queens were collected during a study between May 1998 and October 2000. They had one to six kittens per litter, with an average of three kittens. They produced a mean of 1.4 litters per year, but a maximum of three litters in a year. Of 169 kittens, 127 died before they were six months old due to a trauma caused in most cases by dog attacks and road accidents. The first litter is usually smaller than subsequent litters. Kittens are weaned between six and seven weeks of age. Queens normally reach sexual maturity at 5–10 months, and males at 5–7 months. This varies depending on breed. Kittens reach puberty at the age of 9–10 months.
Cats are ready to go to new homes at about 12 weeks of age, when they are ready to leave their mother. They can be surgically sterilized (spayed or castrated) as early as seven weeks to limit unwanted reproduction. This surgery also prevents undesirable sex-related behavior, such as aggression, territory marking (spraying urine) in males and yowling (calling) in females. Traditionally, this surgery was performed at around six to nine months of age, but it is increasingly being performed before puberty, at about three to six months. In the United States, about 80% of household cats are neutered.
Lifespan and health
Main articles: Cat health and Aging in cats
The average lifespan of pet cats has risen in recent decades. In the early 1980s, it was about seven years,: 33 rising to 9.4 years in 1995: 33 and an average of about 13 years as of 2014 and 2023. Some cats have been reported as surviving into their 30s, with the oldest known cat dying at a verified age of 38.
Neutering increases life expectancy: one study found castrated male cats live twice as long as intact males, while spayed female cats live 62% longer than intact females.: 35 Having a cat neutered confers health benefits, because castrated males cannot develop testicular cancer, spayed females cannot develop uterine or ovarian cancer, and both have a reduced risk of mammary cancer.
Disease
Main article: List of feline diseases
About 250 heritable genetic disorders have been identified in cats, many similar to human inborn errors of metabolism. The high level of similarity among the metabolism of mammals allows many of these feline diseases to be diagnosed using genetic tests that were originally developed for use in humans, as well as the use of cats as animal models in the study of the human diseases. Diseases affecting domestic cats include acute infections, parasitic infestations, injuries, and chronic diseases such as kidney disease, thyroid disease, and arthritis. Vaccinations are available for many infectious diseases, as are treatments to eliminate parasites such as worms, ticks, and fleas.
Ecology
Habitats
The domestic cat is a cosmopolitan species and occurs across much of the world. It is adaptable and now present on all continents except Antarctica, and on 118 of the 131 main groups of islands, even on the isolated Kerguelen Islands. Due to its ability to thrive in almost any terrestrial habitat, it is among the world's most invasive species. It lives on small islands with no human inhabitants. Feral cats can live in forests, grasslands, tundra, coastal areas, agricultural land, scrublands, urban areas, and wetlands.
The unwantedness that leads to the domestic cat being treated as an invasive species is twofold. On one hand, as it is little altered from the wildcat, it can readily interbreed with the wildcat. This hybridization poses a danger to the genetic distinctiveness of some wildcat populations, particularly in Scotland and Hungary, possibly also the Iberian Peninsula, and where protected natural areas are close to human-dominated landscapes, such as Kruger National Park in South Africa. However, its introduction to places where no native felines are present also contributes to the decline of native species.
Ferality
Main article: Feral cat
Feral cats are domestic cats that were born in or have reverted to a wild state. They are unfamiliar with and wary of humans and roam freely in urban and rural areas. The numbers of feral cats is not known, but estimates of the United States feral population range from 25 to 60 million. Feral cats may live alone, but most are found in large colonies, which occupy a specific territory and are usually associated with a source of food. Famous feral cat colonies are found in Rome around the Colosseum and Forum Romanum, with cats at some of these sites being fed and given medical attention by volunteers.
Public attitudes toward feral cats vary widely, from seeing them as free-ranging pets to regarding them as vermin.
Some feral cats can be successfully socialized and 're-tamed' for adoption; young cats, especially kittens and cats that have had prior experience and contact with humans are the most receptive to these efforts.
Impact on wildlife
Main article: Cat predation on wildlife
On islands, birds can contribute as much as 60% of a cat's diet. In nearly all cases, the cat cannot be identified as the sole cause for reducing the numbers of island birds, and in some instances, eradication of cats has caused a "mesopredator release" effect; where the suppression of top carnivores creates an abundance of smaller predators that cause a severe decline in their shared prey. Domestic cats are a contributing factor to the decline of many species, a factor that has ultimately led, in some cases, to extinction. The South Island piopio, Chatham rail, and the New Zealand merganser are a few from a long list, with the most extreme case being the flightless Lyall's wren, which was driven to extinction only a few years after its discovery. One feral cat in New Zealand killed 102 New Zealand lesser short-tailed bats in seven days. In the US, feral and free-ranging domestic cats kill an estimated 6.3 – 22.3 billion mammals annually.
In Australia, the impact of cats on mammal populations is even greater than the impact of habitat loss. More than one million reptiles are killed by feral cats each day, representing 258 species. Cats have contributed to the extinction of the Navassa curly-tailed lizard and Chioninia coctei.
Interaction with humans
Main article: Human interaction with cats
Cats are common pets throughout the world, and their worldwide population as of 2007 exceeded 500 million. As of 2017, the domestic cat was the second most popular pet in the United States, with 95.6 million cats owned and around 42 million households owning at least one cat. In the United Kingdom, 26% of adults have a cat, with an estimated population of 10.9 million pet cats as of 2020. As of 2021, there were an estimated 220 million owned and 480 million stray cats in the world.
Cats have been used for millennia to control rodents, notably around grain stores and aboard ships, and both uses extend to the present day.
As well as being kept as pets, cats are also used in the international fur trade and leather industries for making coats, hats, blankets, stuffed toys, shoes, gloves, and musical instruments. About 24 cats are needed to make a cat-fur coat. This use has been outlawed in the United States since 2000 and in the European Union (as well as the United Kingdom) since 2007.
Cat pelts have been used for superstitious purposes as part of the practice of witchcraft, and are still made into blankets in Switzerland as traditional medicine thought to cure rheumatism.
A few attempts to build a cat census have been made over the years, both through associations or national and international organizations (such as that of the Canadian Federation of Humane Societies) and over the Internet, but such a task does not seem simple to achieve. General estimates for the global population of domestic cats range widely from anywhere between 200 million to 600 million. Walter Chandoha made his career photographing cats after his 1949 images of Loco, an especially charming stray taken in, were published around the world. He is reported to have photographed 90,000 cats during his career and maintained an archive of 225,000 images that he drew from for publications during his lifetime.
Shows
Main article: Cat show
A cat show is a judged event in which the owners of cats compete to win titles in various cat-registering organizations by entering their cats to be judged after a breed standard. It is often required that a cat must be healthy and vaccinated in order to participate in a cat show. Both pedigreed and non-purebred companion ("moggy") cats are admissible, although the rules differ depending on the organization. Competing cats are compared to the applicable breed standard, and assessed for temperament.
Infection
Main article: Feline zoonosis
Cats can be infected or infested with viruses, bacteria, fungus, protozoans, arthropods or worms that can transmit diseases to humans. In some cases, the cat exhibits no symptoms of the disease. The same disease can then become evident in a human. The likelihood that a person will become diseased depends on the age and immune status of the person. Humans who have cats living in their home or in close association are more likely to become infected. Others might also acquire infections from cat feces and parasites exiting the cat's body. Some of the infections of most concern include salmonella, cat-scratch disease and toxoplasmosis.
History and mythology
Main articles: Cultural depictions of cats and Cats in ancient Egypt
In ancient Egypt, cats were worshipped, and the goddess Bastet often depicted in cat form, sometimes taking on the war-like aspect of a lioness. The Greek historian Herodotus reported that killing a cat was forbidden, and when a household cat died, the entire family mourned and shaved their eyebrows. Families took their dead cats to the sacred city of Bubastis, where they were embalmed and buried in sacred repositories. Herodotus expressed astonishment at the domestic cats in Egypt, because he had only ever seen wildcats.
Ancient Greeks and Romans kept weasels as pets, which were seen as the ideal rodent-killers. The earliest unmistakable evidence of the Greeks having domestic cats comes from two coins from Magna Graecia dating to the mid-fifth century BC showing Iokastos and Phalanthos, the legendary founders of Rhegion and Taras respectively, playing with their pet cats. The usual ancient Greek word for 'cat' was ailouros, meaning 'thing with the waving tail'. Cats are rarely mentioned in ancient Greek literature. Aristotle remarked in his History of Animals that "female cats are naturally lecherous." The Greeks later syncretized their own goddess Artemis with the Egyptian goddess Bastet, adopting Bastet's associations with cats and ascribing them to Artemis. In Ovid's Metamorphoses, when the deities flee to Egypt and take animal forms, the goddess Diana turns into a cat.
Cats eventually displaced weasels as the pest control of choice because they were more pleasant to have around the house and were more enthusiastic hunters of mice. During the Middle Ages, many of Artemis's associations with cats were grafted onto the Virgin Mary. Cats are often shown in icons of Annunciation and of the Holy Family and, according to Italian folklore, on the same night that Mary gave birth to Jesus, a cat in Bethlehem gave birth to a kitten. Domestic cats were spread throughout much of the rest of the world during the Age of Discovery, as ships' cats were carried on sailing ships to control shipboard rodents and as good-luck charms.
Several ancient religions believed cats are exalted souls, companions or guides for humans, that are all-knowing but mute so they cannot influence decisions made by humans. In Japan, the maneki neko cat is a symbol of good fortune. In Norse mythology, Freyja, the goddess of love, beauty, and fertility, is depicted as riding a chariot drawn by cats. In Jewish legend, the first cat was living in the house of the first man Adam as a pet that got rid of mice. The cat was once partnering with the first dog before the latter broke an oath they had made which resulted in enmity between the descendants of these two animals. It is also written that neither cats nor foxes are represented in the water, while every other animal has an incarnation species in the water. Although no species are sacred in Islam, cats are revered by Muslims. Some Western writers have stated Muhammad had a favorite cat, Muezza. He is reported to have loved cats so much, "he would do without his cloak rather than disturb one that was sleeping on it". The story has no origin in early Muslim writers, and seems to confuse a story of a later Sufi saint, Ahmed ar-Rifa'i, centuries after Muhammad. One of the companions of Muhammad was known as Abu Hurayrah ("father of the kitten"), in reference to his documented affection to cats.
Superstitions and rituals
Many cultures have negative superstitions about cats. An example would be the belief that encountering a black cat ("crossing one's path") leads to bad luck, or that cats are witches' familiars used to augment a witch's powers and skills. The killing of cats in Medieval Ypres, Belgium, is commemorated in the innocuous present-day Kattenstoet (cat parade). In mid-16th century France, cats would be burnt alive as a form of entertainment, particularly during midsummer festivals. According to Norman Davies, the assembled people "shrieked with laughter as the animals, howling with pain, were singed, roasted, and finally carbonized". The remaining ashes were sometimes taken back home by the people for good luck.
According to a myth in many cultures, cats have multiple lives. In many countries, they are believed to have nine lives, but in Italy, Germany, Greece, Brazil and some Spanish-speaking regions, they are said to have seven lives, while in Arabic traditions, the number of lives is six. An early mention of the myth can be found in John Heywood's The Proverbs of John Heywood (1546)
Husband, (quoth she), ye studie, be merrie now,
And even as ye thinke now, so come to yow.
Nay not so, (quoth he), for my thought to tell right,
I thinke how you lay groning, wife, all last night.
Husband, a groning horse and a groning wife
Never faile their master, (quoth she), for my life.
No wife, a woman hath nine lives like a cat.
The myth is attributed to the natural suppleness and swiftness cats exhibit to escape life-threatening situations. Also lending credence to this myth is the fact that falling cats often land on their feet, using an instinctive righting reflex to twist their bodies around. Nonetheless, cats can still be injured or killed by a high fall.
Another fly portrait, I'm afraid, but living in the wet & windy UK sometimes that's all that there is. I love the eyes on these creatures, what an evolutionary trick!
[EDIT}
Compound Eyes
The type of eye comonly found in arthropods, including many insects and crustacea. A compound eye has a meshlike appearance because it consists of hundreds or thousands of tiny lens-capped optical units called ommatidia. Each ommatidium has its own cornea, lens, and photoreceptor cells for distinguishing brightness and color. Individual ommatidia guide light through a lens and cone into a channel, known as a rhabdom, which contains light-sensitive cells. These are connected to optical nerve cells to produce the image. The ommatidia are seperated from each other by varying degrees of pigment.
The ommatidia are packed side by side into bulges that create a wide field of view. As each unit is orientated in a slightly different direction, the honeycombed eye creates a mosaic image which, although poor at picking out detail, is excellent at detecting movement.
The two main kinds of compound eyes
According to the structure of a compound eye, and the way pigment is distributed between the ommatidia, the eye can form either apposition images or superposition images. In the case of an apposition eye, each ommatidium focuses only rays that are almost parallel to its long axis, so that each forms an image of only a very small part of the visual field. The image of the whole results from combination of these part images.
In the case of a superposition eye, the sensory cells of an ommatidium can pick up light from a large part of the visual field so that the image received may overlap those received by as many as 30 neighboring ommatidia. The superposition image thus gains in brightness but loses in sharpness compared with the apposition image.
Diurnal insects have apposition eyes, whereas nocturnal insects have superposition eyes. However, there are many intermediate grades and, in some animals, one type of eye may change temporarily into the other by movement of pigment between the ommatidia to allow adaptation to the dark.
Compound eyes first appeared on Earth more than 500 million years ago. We know this because they can be seen on fossil trilobites of this age.
How good are compound eyes?
Compared with single-aperture eyes, such as the human eye, compound eyes have poor resolution so they are not good at making out detail. On the other hand, compound eyes have a very large angle of view and the ability to detect fast movement and, in some cases, the polarization of light. Insects that can fly well, such as honey bees and flies, or that catch prey, such as dragonflies or preying mantis, have specialized zones of ommatidia. These zones are organized into a fovea area that gives acute vision. In the acute zone, the eye is flattened and the facets are larger, which allows more ommatidia to receive light from a spot and thereby achieve higher resolution.
Compound eyes generally allow only a short range of vision. For example, flies and mosquitoes can see only a few millimeters in front of them with any degree of resolution, although within this short range they can see detail that we could see only with a microscope.
Dragonflies have one of the most elaborate eyes of any insect, capable of pinpointing the motion of a small prey insect several meters away, even his while the dragonfly is traveling fast. Butterflies have color vision that is more enhanced than our own, enabling them to locate food from flowers. Honey bees can see in ultraviolet, which allows them to perceive patterns on nectar-laden flowers that are invisible to us. Many insects, including bees, can also detect polarized light, which they use in navigation.
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Fish, any of approximately 34,000 species of vertebrate animals (phylum Chordata) found in the fresh and salt waters of the world. Living species range from the primitive jawless lampreys and hagfishes through the cartilaginous sharks, skates, and rays to the abundant and diverse bony fishes. Most fish species are cold-blooded; however, one species, the opah (Lampris guttatus), is warm-blooded.
The term fish is applied to a variety of vertebrates of several evolutionary lines. It describes a life-form rather than a taxonomic group. As members of the phylum Chordata, fish share certain features with other vertebrates. These features are gill slits at some point in the life cycle, a notochord, or skeletal supporting rod, a dorsal hollow nerve cord, and a tail. Living fishes represent some five classes, which are as distinct from one another as are the four classes of familiar air-breathing animals—amphibians, reptiles, birds, and mammals. For example, the jawless fishes (Agnatha) have gills in pouches and lack limb girdles. Extant agnathans are the lampreys and the hagfishes. As the name implies, the skeletons of fishes of the class Chondrichthyes (from chondr, “cartilage,” and ichthyes, “fish”) are made entirely of cartilage. Modern fish of this class lack a swim bladder, and their scales and teeth are made up of the same placoid material. Sharks, skates, and rays are examples of cartilaginous fishes. The bony fishes are by far the largest class. Examples range from the tiny seahorse to the 450-kg (1,000-pound) blue marlin, from the flattened soles and flounders to the boxy puffers and ocean sunfishes. Unlike the scales of the cartilaginous fishes, those of bony fishes, when present, grow throughout life and are made up of thin overlapping plates of bone. Bony fishes also have an operculum that covers the gill slits.
The study of fishes, the science of ichthyology, is of broad importance. Fishes are of interest to humans for many reasons, the most important being their relationship with and dependence on the environment. A more obvious reason for interest in fishes is their role as a moderate but important part of the world’s food supply. This resource, once thought unlimited, is now realized to be finite and in delicate balance with the biological, chemical, and physical factors of the aquatic environment. Overfishing, pollution, and alteration of the environment are the chief enemies of proper fisheries management, both in fresh waters and in the ocean. (For a detailed discussion of the technology and economics of fisheries, see commercial fishing.) Another practical reason for studying fishes is their use in disease control. As predators on mosquito larvae, they help curb malaria and other mosquito-borne diseases.
Fishes are valuable laboratory animals in many aspects of medical and biological research. For example, the readiness of many fishes to acclimate to captivity has allowed biologists to study behaviour, physiology, and even ecology under relatively natural conditions. Fishes have been especially important in the study of animal behaviour, where research on fishes has provided a broad base for the understanding of the more flexible behaviour of the higher vertebrates. The zebra fish is used as a model in studies of gene expression.
There are aesthetic and recreational reasons for an interest in fishes. Millions of people keep live fishes in home aquariums for the simple pleasure of observing the beauty and behaviour of animals otherwise unfamiliar to them. Aquarium fishes provide a personal challenge to many aquarists, allowing them to test their ability to keep a small section of the natural environment in their homes. Sportfishing is another way of enjoying the natural environment, also indulged in by millions of people every year. Interest in aquarium fishes and sportfishing supports multimillion-dollar industries throughout the world.
Fishes have been in existence for more than 450 million years, during which time they have evolved repeatedly to fit into almost every conceivable type of aquatic habitat. In a sense, land vertebrates are simply highly modified fishes: when fishes colonized the land habitat, they became tetrapod (four-legged) land vertebrates. The popular conception of a fish as a slippery, streamlined aquatic animal that possesses fins and breathes by gills applies to many fishes, but far more fishes deviate from that conception than conform to it. For example, the body is elongate in many forms and greatly shortened in others; the body is flattened in some (principally in bottom-dwelling fishes) and laterally compressed in many others; the fins may be elaborately extended, forming intricate shapes, or they may be reduced or even lost; and the positions of the mouth, eyes, nostrils, and gill openings vary widely. Air breathers have appeared in several evolutionary lines.
Many fishes are cryptically coloured and shaped, closely matching their respective environments; others are among the most brilliantly coloured of all organisms, with a wide range of hues, often of striking intensity, on a single individual. The brilliance of pigments may be enhanced by the surface structure of the fish, so that it almost seems to glow. A number of unrelated fishes have actual light-producing organs. Many fishes are able to alter their coloration—some for the purpose of camouflage, others for the enhancement of behavioral signals.
Fishes range in adult length from less than 10 mm (0.4 inch) to more than 20 metres (60 feet) and in weight from about 1.5 grams (less than 0.06 ounce) to many thousands of kilograms. Some live in shallow thermal springs at temperatures slightly above 42 °C (100 °F), others in cold Arctic seas a few degrees below 0 °C (32 °F) or in cold deep waters more than 4,000 metres (13,100 feet) beneath the ocean surface. The structural and, especially, the physiological adaptations for life at such extremes are relatively poorly known and provide the scientifically curious with great incentive for study.
Almost all natural bodies of water bear fish life, the exceptions being very hot thermal ponds and extremely salt-alkaline lakes, such as the Dead Sea in Asia and the Great Salt Lake in North America. The present distribution of fishes is a result of the geological history and development of Earth as well as the ability of fishes to undergo evolutionary change and to adapt to the available habitats. Fishes may be seen to be distributed according to habitat and according to geographical area. Major habitat differences are marine and freshwater. For the most part, the fishes in a marine habitat differ from those in a freshwater habitat, even in adjacent areas, but some, such as the salmon, migrate from one to the other. The freshwater habitats may be seen to be of many kinds. Fishes found in mountain torrents, Arctic lakes, tropical lakes, temperate streams, and tropical rivers will all differ from each other, both in obvious gross structure and in physiological attributes. Even in closely adjacent habitats where, for example, a tropical mountain torrent enters a lowland stream, the fish fauna will differ. The marine habitats can be divided into deep ocean floors (benthic), mid-water oceanic (bathypelagic), surface oceanic (pelagic), rocky coast, sandy coast, muddy shores, bays, estuaries, and others. Also, for example, rocky coastal shores in tropical and temperate regions will have different fish faunas, even when such habitats occur along the same coastline.
Although much is known about the present geographical distribution of fishes, far less is known about how that distribution came about. Many parts of the fish fauna of the fresh waters of North America and Eurasia are related and undoubtedly have a common origin. The faunas of Africa and South America are related, extremely old, and probably an expression of the drifting apart of the two continents. The fauna of southern Asia is related to that of Central Asia, and some of it appears to have entered Africa. The extremely large shore-fish faunas of the Indian and tropical Pacific oceans comprise a related complex, but the tropical shore fauna of the Atlantic, although containing Indo-Pacific components, is relatively limited and probably younger. The Arctic and Antarctic marine faunas are quite different from each other. The shore fauna of the North Pacific is quite distinct, and that of the North Atlantic more limited and probably younger. Pelagic oceanic fishes, especially those in deep waters, are similar the world over, showing little geographical isolation in terms of family groups. The deep oceanic habitat is very much the same throughout the world, but species differences do exist, showing geographical areas determined by oceanic currents and water masses.
All aspects of the life of a fish are closely correlated with adaptation to the total environment, physical, chemical, and biological. In studies, all the interdependent aspects of fish, such as behaviour, locomotion, reproduction, and physical and physiological characteristics, must be taken into account.
Correlated with their adaptation to an extremely wide variety of habitats is the extremely wide variety of life cycles that fishes display. The great majority hatch from relatively small eggs a few days to several weeks or more after the eggs are scattered in the water. Newly hatched young are still partially undeveloped and are called larvae until body structures such as fins, skeleton, and some organs are fully formed. Larval life is often very short, usually less than a few weeks, but it can be very long, some lampreys continuing as larvae for at least five years. Young and larval fishes, before reaching sexual maturity, must grow considerably, and their small size and other factors often dictate that they live in a habitat different than that of the adults. For example, most tropical marine shore fishes have pelagic larvae. Larval food also is different, and larval fishes often live in shallow waters, where they may be less exposed to predators.
After a fish reaches adult size, the length of its life is subject to many factors, such as innate rates of aging, predation pressure, and the nature of the local climate. The longevity of a species in the protected environment of an aquarium may have nothing to do with how long members of that species live in the wild. Many small fishes live only one to three years at the most. In some species, however, individuals may live as long as 10 or 20 or even 100 years.
Fish behaviour is a complicated and varied subject. As in almost all animals with a central nervous system, the nature of a response of an individual fish to stimuli from its environment depends upon the inherited characteristics of its nervous system, on what it has learned from past experience, and on the nature of the stimuli. Compared with the variety of human responses, however, that of a fish is stereotyped, not subject to much modification by “thought” or learning, and investigators must guard against anthropomorphic interpretations of fish behaviour.
Fishes perceive the world around them by the usual senses of sight, smell, hearing, touch, and taste and by special lateral line water-current detectors. In the few fishes that generate electric fields, a process that might best be called electrolocation aids in perception. One or another of these senses often is emphasized at the expense of others, depending upon the fish’s other adaptations. In fishes with large eyes, the sense of smell may be reduced; others, with small eyes, hunt and feed primarily by smell (such as some eels).
Specialized behaviour is primarily concerned with the three most important activities in the fish’s life: feeding, reproduction, and escape from enemies. Schooling behaviour of sardines on the high seas, for instance, is largely a protective device to avoid enemies, but it is also associated with and modified by their breeding and feeding requirements. Predatory fishes are often solitary, lying in wait to dart suddenly after their prey, a kind of locomotion impossible for beaked parrot fishes, which feed on coral, swimming in small groups from one coral head to the next. In addition, some predatory fishes that inhabit pelagic environments, such as tunas, often school.
Sleep in fishes, all of which lack true eyelids, consists of a seemingly listless state in which the fish maintains its balance but moves slowly. If attacked or disturbed, most can dart away. A few kinds of fishes lie on the bottom to sleep. Most catfishes, some loaches, and some eels and electric fishes are strictly nocturnal, being active and hunting for food during the night and retiring during the day to holes, thick vegetation, or other protective parts of the environment.
Communication between members of a species or between members of two or more species often is extremely important, especially in breeding behaviour (see below Reproduction). The mode of communication may be visual, as between the small so-called cleaner fish and a large fish of a very different species. The larger fish often allows the cleaner to enter its mouth to remove gill parasites. The cleaner is recognized by its distinctive colour and actions and therefore is not eaten, even if the larger fish is normally a predator. Communication is often chemical, signals being sent by specific chemicals called pheromones.
Many fishes have a streamlined body and swim freely in open water. Fish locomotion is closely correlated with habitat and ecological niche (the general position of the animal to its environment).
Many fishes in both marine and fresh waters swim at the surface and have mouths adapted to feed best (and sometimes only) at the surface. Often such fishes are long and slender, able to dart at surface insects or at other surface fishes and in turn to dart away from predators; needlefishes, halfbeaks, and topminnows (such as killifish and mosquito fish) are good examples. Oceanic flying fishes escape their predators by gathering speed above the water surface, with the lower lobe of the tail providing thrust in the water. They then glide hundreds of yards on enlarged, winglike pectoral and pelvic fins. South American freshwater flying fishes escape their enemies by jumping and propelling their strongly keeled bodies out of the water.
So-called mid-water swimmers, the most common type of fish, are of many kinds and live in many habitats. The powerful fusiform tunas and the trouts, for example, are adapted for strong, fast swimming, the tunas to capture prey speedily in the open ocean and the trouts to cope with the swift currents of streams and rivers. The trout body form is well adapted to many habitats. Fishes that live in relatively quiet waters such as bays or lake shores or slow rivers usually are not strong, fast swimmers but are capable of short, quick bursts of speed to escape a predator. Many of these fishes have their sides flattened, examples being the sunfish and the freshwater angelfish of aquarists. Fish associated with the bottom or substrate usually are slow swimmers. Open-water plankton-feeding fishes almost always remain fusiform and are capable of rapid, strong movement (for example, sardines and herrings of the open ocean and also many small minnows of streams and lakes).
Bottom-living fishes are of many kinds and have undergone many types of modification of their body shape and swimming habits. Rays, which evolved from strong-swimming mid-water sharks, usually stay close to the bottom and move by undulating their large pectoral fins. Flounders live in a similar habitat and move over the bottom by undulating the entire body. Many bottom fishes dart from place to place, resting on the bottom between movements, a motion common in gobies. One goby relative, the mudskipper, has taken to living at the edge of pools along the shore of muddy mangrove swamps. It escapes its enemies by flipping rapidly over the mud, out of the water. Some catfishes, synbranchid eels, the so-called climbing perch, and a few other fishes venture out over damp ground to find more promising waters than those that they left. They move by wriggling their bodies, sometimes using strong pectoral fins; most have accessory air-breathing organs. Many bottom-dwelling fishes live in mud holes or rocky crevices. Marine eels and gobies commonly are found in such habitats and for the most part venture far beyond their cavelike homes. Some bottom dwellers, such as the clingfishes (Gobiesocidae), have developed powerful adhesive disks that enable them to remain in place on the substrate in areas such as rocky coasts, where the action of the waves is great.
The methods of reproduction in fishes are varied, but most fishes lay a large number of small eggs, fertilized and scattered outside of the body. The eggs of pelagic fishes usually remain suspended in the open water. Many shore and freshwater fishes lay eggs on the bottom or among plants. Some have adhesive eggs. The mortality of the young and especially of the eggs is very high, and often only a few individuals grow to maturity out of hundreds, thousands, and in some cases millions of eggs laid.
Males produce sperm, usually as a milky white substance called milt, in two (sometimes one) testes within the body cavity. In bony fishes a sperm duct leads from each testis to a urogenital opening behind the vent or anus. In sharks and rays and in cyclostomes the duct leads to a cloaca. Sometimes the pelvic fins are modified to help transmit the milt to the eggs at the female’s vent or on the substrate where the female has placed them. Sometimes accessory organs are used to fertilize females internally—for example, the claspers of many sharks and rays.
In the females the eggs are formed in two ovaries (sometimes only one) and pass through the ovaries to the urogenital opening and to the outside. In some fishes the eggs are fertilized internally but are shed before development takes place. Members of about a dozen families each of bony fishes (teleosts) and sharks bear live young. Many skates and rays also bear live young. In some bony fishes the eggs simply develop within the female, the young emerging when the eggs hatch (ovoviviparous). Others develop within the ovary and are nourished by ovarian tissues after hatching (viviparous). There are also other methods utilized by fishes to nourish young within the female. In all live-bearers the young are born at a relatively large size and are few in number. In one family of primarily marine fishes, the surfperches from the Pacific coast of North America, Japan, and Korea, the males of at least one species are born sexually mature, although they are not fully grown.
Some fishes are hermaphroditic—an individual producing both sperm and eggs, usually at different stages of its life. Self-fertilization, however, is probably rare.
Successful reproduction and, in many cases, defense of the eggs and the young are assured by rather stereotypical but often elaborate courtship and parental behaviour, either by the male or the female or both. Some fishes prepare nests by hollowing out depressions in the sand bottom (cichlids, for example), build nests with plant materials and sticky threads excreted by the kidneys (sticklebacks), or blow a cluster of mucus-covered bubbles at the water surface (gouramis). The eggs are laid in these structures. Some varieties of cichlids and catfishes incubate eggs in their mouths.
Some fishes, such as salmon, undergo long migrations from the ocean and up large rivers to spawn in the gravel beds where they themselves hatched (anadromous fishes). Some, such as the freshwater eels (family Anguillidae), live and grow to maturity in fresh water and migrate to the sea to spawn (catadromous fishes). Other fishes undertake shorter migrations from lakes into streams, within the ocean, or enter spawning habitats that they do not ordinarily occupy in other ways.
The basic structure and function of the fish body are similar to those of all other vertebrates. The usual four types of tissues are present: surface or epithelial, connective (bone, cartilage, and fibrous tissues, as well as their derivative, blood), nerve, and muscle tissues. In addition, the fish’s organs and organ systems parallel those of other vertebrates.
The typical fish body is streamlined and spindle-shaped, with an anterior head, a gill apparatus, and a heart, the latter lying in the midline just below the gill chamber. The body cavity, containing the vital organs, is situated behind the head in the lower anterior part of the body. The anus usually marks the posterior termination of the body cavity and most often occurs just in front of the base of the anal fin. The spinal cord and vertebral column continue from the posterior part of the head to the base of the tail fin, passing dorsal to the body cavity and through the caudal (tail) region behind the body cavity. Most of the body is of muscular tissue, a high proportion of which is necessitated by swimming. In the course of evolution this basic body plan has been modified repeatedly into the many varieties of fish shapes that exist today.
The skeleton forms an integral part of the fish’s locomotion system, as well as serving to protect vital parts. The internal skeleton consists of the skull bones (except for the roofing bones of the head, which are really part of the external skeleton), the vertebral column, and the fin supports (fin rays). The fin supports are derived from the external skeleton but will be treated here because of their close functional relationship to the internal skeleton. The internal skeleton of cyclostomes, sharks, and rays is of cartilage; that of many fossil groups and some primitive living fishes is mostly of cartilage but may include some bone. In place of the vertebral column, the earliest vertebrates had a fully developed notochord, a flexible stiff rod of viscous cells surrounded by a strong fibrous sheath. During the evolution of modern fishes the rod was replaced in part by cartilage and then by ossified cartilage. Sharks and rays retain a cartilaginous vertebral column; bony fishes have spool-shaped vertebrae that in the more primitive living forms only partially replace the notochord. The skull, including the gill arches and jaws of bony fishes, is fully, or at least partially, ossified. That of sharks and rays remains cartilaginous, at times partially replaced by calcium deposits but never by true bone.
The supportive elements of the fins (basal or radial bones or both) have changed greatly during fish evolution. Some of these changes are described in the section below (Evolution and paleontology). Most fishes possess a single dorsal fin on the midline of the back. Many have two and a few have three dorsal fins. The other fins are the single tail and anal fins and paired pelvic and pectoral fins. A small fin, the adipose fin, with hairlike fin rays, occurs in many of the relatively primitive teleosts (such as trout) on the back near the base of the caudal fin.
The skin of a fish must serve many functions. It aids in maintaining the osmotic balance, provides physical protection for the body, is the site of coloration, contains sensory receptors, and, in some fishes, functions in respiration. Mucous glands, which aid in maintaining the water balance and offer protection from bacteria, are extremely numerous in fish skin, especially in cyclostomes and teleosts. Since mucous glands are present in the modern lampreys, it is reasonable to assume that they were present in primitive fishes, such as the ancient Silurian and Devonian agnathans. Protection from abrasion and predation is another function of the fish skin, and dermal (skin) bone arose early in fish evolution in response to this need. It is thought that bone first evolved in skin and only later invaded the cartilaginous areas of the fish’s body, to provide additional support and protection. There is some argument as to which came first, cartilage or bone, and fossil evidence does not settle the question. In any event, dermal bone has played an important part in fish evolution and has different characteristics in different groups of fishes. Several groups are characterized at least in part by the kind of bony scales they possess.
Scales have played an important part in the evolution of fishes. Primitive fishes usually had thick bony plates or thick scales in several layers of bone, enamel, and related substances. Modern teleost fishes have scales of bone, which, while still protective, allow much more freedom of motion in the body. A few modern teleosts (some catfishes, sticklebacks, and others) have secondarily acquired bony plates in the skin. Modern and early sharks possessed placoid scales, a relatively primitive type of scale with a toothlike structure, consisting of an outside layer of enamel-like substance (vitrodentine), an inner layer of dentine, and a pulp cavity containing nerves and blood vessels. Primitive bony fishes had thick scales of either the ganoid or the cosmoid type. Cosmoid scales have a hard, enamel-like outer layer, an inner layer of cosmine (a form of dentine), and then a layer of vascular bone (isopedine). In ganoid scales the hard outer layer is different chemically and is called ganoin. Under this is a cosminelike layer and then a vascular bony layer. The thin, translucent bony scales of modern fishes, called cycloid and ctenoid (the latter distinguished by serrations at the edges), lack enameloid and dentine layers.
Skin has several other functions in fishes. It is well supplied with nerve endings and presumably receives tactile, thermal, and pain stimuli. Skin is also well supplied with blood vessels. Some fishes breathe in part through the skin, by the exchange of oxygen and carbon dioxide between the surrounding water and numerous small blood vessels near the skin surface.
Skin serves as protection through the control of coloration. Fishes exhibit an almost limitless range of colours. The colours often blend closely with the surroundings, effectively hiding the animal. Many fishes use bright colours for territorial advertisement or as recognition marks for other members of their own species, or sometimes for members of other species. Many fishes can change their colour to a greater or lesser degree, by movement of pigment within the pigment cells (chromatophores). Black pigment cells (melanophores), of almost universal occurrence in fishes, are often juxtaposed with other pigment cells. When placed beneath iridocytes or leucophores (bearing the silvery or white pigment guanine), melanophores produce structural colours of blue and green. These colours are often extremely intense, because they are formed by refraction of light through the needlelike crystals of guanine. The blue and green refracted colours are often relatively pure, lacking the red and yellow rays, which have been absorbed by the black pigment (melanin) of the melanophores. Yellow, orange, and red colours are produced by erythrophores, cells containing the appropriate carotenoid pigments. Other colours are produced by combinations of melanophores, erythrophores, and iridocytes.
The major portion of the body of most fishes consists of muscles. Most of the mass is trunk musculature, the fin muscles usually being relatively small. The caudal fin is usually the most powerful fin, being moved by the trunk musculature. The body musculature is usually arranged in rows of chevron-shaped segments on each side. Contractions of these segments, each attached to adjacent vertebrae and vertebral processes, bends the body on the vertebral joint, producing successive undulations of the body, passing from the head to the tail, and producing driving strokes of the tail. It is the latter that provides the strong forward movement for most fishes.
The digestive system, in a functional sense, starts at the mouth, with the teeth used to capture prey or collect plant foods. Mouth shape and tooth structure vary greatly in fishes, depending on the kind of food normally eaten. Most fishes are predacious, feeding on small invertebrates or other fishes and have simple conical teeth on the jaws, on at least some of the bones of the roof of the mouth, and on special gill arch structures just in front of the esophagus. The latter are throat teeth. Most predacious fishes swallow their prey whole, and the teeth are used for grasping and holding prey, for orienting prey to be swallowed (head first) and for working the prey toward the esophagus. There are a variety of tooth types in fishes. Some fishes, such as sharks and piranhas, have cutting teeth for biting chunks out of their victims. A shark’s tooth, although superficially like that of a piranha, appears in many respects to be a modified scale, while that of the piranha is like that of other bony fishes, consisting of dentine and enamel. Parrot fishes have beaklike mouths with short incisor-like teeth for breaking off coral and have heavy pavementlike throat teeth for crushing the coral. Some catfishes have small brushlike teeth, arranged in rows on the jaws, for scraping plant and animal growth from rocks. Many fishes (such as the Cyprinidae or minnows) have no jaw teeth at all but have very strong throat teeth.
Some fishes gather planktonic food by straining it from their gill cavities with numerous elongate stiff rods (gill rakers) anchored by one end to the gill bars. The food collected on these rods is passed to the throat, where it is swallowed. Most fishes have only short gill rakers that help keep food particles from escaping out the mouth cavity into the gill chamber.
Once reaching the throat, food enters a short, often greatly distensible esophagus, a simple tube with a muscular wall leading into a stomach. The stomach varies greatly in fishes, depending upon the diet. In most predacious fishes it is a simple straight or curved tube or pouch with a muscular wall and a glandular lining. Food is largely digested there and leaves the stomach in liquid form.
Between the stomach and the intestine, ducts enter the digestive tube from the liver and pancreas. The liver is a large, clearly defined organ. The pancreas may be embedded in it, diffused through it, or broken into small parts spread along some of the intestine. The junction between the stomach and the intestine is marked by a muscular valve. Pyloric ceca (blind sacs) occur in some fishes at this junction and have a digestive or absorptive function or both.
The intestine itself is quite variable in length, depending upon the fish’s diet. It is short in predacious forms, sometimes no longer than the body cavity, but long in herbivorous forms, being coiled and several times longer than the entire length of the fish in some species of South American catfishes. The intestine is primarily an organ for absorbing nutrients into the bloodstream. The larger its internal surface, the greater its absorptive efficiency, and a spiral valve is one method of increasing its absorption surface.
Sharks, rays, chimaeras, lungfishes, surviving chondrosteans, holosteans, and even a few of the more primitive teleosts have a spiral valve or at least traces of it in the intestine. Most modern teleosts have increased the area of the intestinal walls by having numerous folds and villi (fingerlike projections) somewhat like those in humans. Undigested substances are passed to the exterior through the anus in most teleost fishes. In lungfishes, sharks, and rays, it is first passed through the cloaca, a common cavity receiving the intestinal opening and the ducts from the urogenital system.
Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills. The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour. Water taken in continuously through the mouth passes backward between the gill bars and over the gill filaments, where the exchange of gases takes place. The gills are protected by a gill cover in teleosts and many other fishes but by flaps of skin in sharks, rays, and some of the older fossil fish groups. The blood capillaries in the gill filaments are close to the gill surface to take up oxygen from the water and to give up excess carbon dioxide to the water.
Most modern fishes have a hydrostatic (ballast) organ, called the swim bladder, that lies in the body cavity just below the kidney and above the stomach and intestine. It originated as a diverticulum of the digestive canal. In advanced teleosts, especially the acanthopterygians, the bladder has lost its connection with the digestive tract, a condition called physoclistic. The connection has been retained (physostomous) by many relatively primitive teleosts. In several unrelated lines of fishes, the bladder has become specialized as a lung or, at least, as a highly vascularized accessory breathing organ. Some fishes with such accessory organs are obligate air breathers and will drown if denied access to the surface, even in well-oxygenated water. Fishes with a hydrostatic form of swim bladder can control their depth by regulating the amount of gas in the bladder. The gas, mostly oxygen, is secreted into the bladder by special glands, rendering the fish more buoyant; the gas is absorbed into the bloodstream by another special organ, reducing the overall buoyancy and allowing the fish to sink. Some deep-sea fishes may have oils, rather than gas, in the bladder. Other deep-sea and some bottom-living forms have much-reduced swim bladders or have lost the organ entirely.
The swim bladder of fishes follows the same developmental pattern as the lungs of land vertebrates. There is no doubt that the two structures have the same historical origin in primitive fishes. More or less intermediate forms still survive among the more primitive types of fishes, such as the lungfishes Lepidosiren and Protopterus.
The circulatory, or blood vascular, system consists of the heart, the arteries, the capillaries, and the veins. It is in the capillaries that the interchange of oxygen, carbon dioxide, nutrients, and other substances such as hormones and waste products takes place. The capillaries lead to the veins, which return the venous blood with its waste products to the heart, kidneys, and gills. There are two kinds of capillary beds: those in the gills and those in the rest of the body. The heart, a folded continuous muscular tube with three or four saclike enlargements, undergoes rhythmic contractions and receives venous blood in a sinus venosus. It passes the blood to an auricle and then into a thick muscular pump, the ventricle. From the ventricle the blood goes to a bulbous structure at the base of a ventral aorta just below the gills. The blood passes to the afferent (receiving) arteries of the gill arches and then to the gill capillaries. There waste gases are given off to the environment, and oxygen is absorbed. The oxygenated blood enters efferent (exuant) arteries of the gill arches and then flows into the dorsal aorta. From there blood is distributed to the tissues and organs of the body. One-way valves prevent backflow. The circulation of fishes thus differs from that of the reptiles, birds, and mammals in that oxygenated blood is not returned to the heart prior to distribution to the other parts of the body.
The primary excretory organ in fishes, as in other vertebrates, is the kidney. In fishes some excretion also takes place in the digestive tract, skin, and especially the gills (where ammonia is given off). Compared with land vertebrates, fishes have a special problem in maintaining their internal environment at a constant concentration of water and dissolved substances, such as salts. Proper balance of the internal environment (homeostasis) of a fish is in a great part maintained by the excretory system, especially the kidney.
The kidney, gills, and skin play an important role in maintaining a fish’s internal environment and checking the effects of osmosis. Marine fishes live in an environment in which the water around them has a greater concentration of salts than they can have inside their body and still maintain life. Freshwater fishes, on the other hand, live in water with a much lower concentration of salts than they require inside their bodies. Osmosis tends to promote the loss of water from the body of a marine fish and absorption of water by that of a freshwater fish. Mucus in the skin tends to slow the process but is not a sufficient barrier to prevent the movement of fluids through the permeable skin. When solutions on two sides of a permeable membrane have different concentrations of dissolved substances, water will pass through the membrane into the more concentrated solution, while the dissolved chemicals move into the area of lower concentration (diffusion).
The kidney of freshwater fishes is often larger in relation to body weight than that of marine fishes. In both groups the kidney excretes wastes from the body, but the kidney of freshwater fishes also excretes large amounts of water, counteracting the water absorbed through the skin. Freshwater fishes tend to lose salt to the environment and must replace it. They get some salt from their food, but the gills and skin inside the mouth actively absorb salt from water passed through the mouth. This absorption is performed by special cells capable of moving salts against the diffusion gradient. Freshwater fishes drink very little water and take in little water with their food.
Marine fishes must conserve water, and therefore their kidneys excrete little water. To maintain their water balance, marine fishes drink large quantities of seawater, retaining most of the water and excreting the salt. Most nitrogenous waste in marine fishes appears to be secreted by the gills as ammonia. Marine fishes can excrete salt by clusters of special cells (chloride cells) in the gills.
There are several teleosts—for example, the salmon—that travel between fresh water and seawater and must adjust to the reversal of osmotic gradients. They adjust their physiological processes by spending time (often surprisingly little time) in the intermediate brackish environment.
Marine hagfishes, sharks, and rays have osmotic concentrations in their blood about equal to that of seawater and so do not have to drink water nor perform much physiological work to maintain their osmotic balance. In sharks and rays the osmotic concentration is kept high by retention of urea in the blood. Freshwater sharks have a lowered concentration of urea in the blood.
Endocrine glands secrete their products into the bloodstream and body tissues and, along with the central nervous system, control and regulate many kinds of body functions. Cyclostomes have a well-developed endocrine system, and presumably it was well developed in the early Agnatha, ancestral to modern fishes. Although the endocrine system in fishes is similar to that of higher vertebrates, there are numerous differences in detail. The pituitary, the thyroid, the suprarenals, the adrenals, the pancreatic islets, the sex glands (ovaries and testes), the inner wall of the intestine, and the bodies of the ultimobranchial gland make up the endocrine system in fishes. There are some others whose function is not well understood. These organs regulate sexual activity and reproduction, growth, osmotic pressure, general metabolic activities such as the storage of fat and the utilization of foodstuffs, blood pressure, and certain aspects of skin colour. Many of these activities are also controlled in part by the central nervous system, which works with the endocrine system in maintaining the life of a fish. Some parts of the endocrine system are developmentally, and undoubtedly evolutionarily, derived from the nervous system.
As in all vertebrates, the nervous system of fishes is the primary mechanism coordinating body activities, as well as integrating these activities in the appropriate manner with stimuli from the environment. The central nervous system, consisting of the brain and spinal cord, is the primary integrating mechanism. The peripheral nervous system, consisting of nerves that connect the brain and spinal cord to various body organs, carries sensory information from special receptor organs such as the eyes, internal ears, nares (sense of smell), taste glands, and others to the integrating centres of the brain and spinal cord. The peripheral nervous system also carries information via different nerve cells from the integrating centres of the brain and spinal cord. This coded information is carried to the various organs and body systems, such as the skeletal muscular system, for appropriate action in response to the original external or internal stimulus. Another branch of the nervous system, the autonomic nervous system, helps to coordinate the activities of many glands and organs and is itself closely connected to the integrating centres of the brain.
The brain of the fish is divided into several anatomical and functional parts, all closely interconnected but each serving as the primary centre of integrating particular kinds of responses and activities. Several of these centres or parts are primarily associated with one type of sensory perception, such as sight, hearing, or smell (olfaction).
The sense of smell is important in almost all fishes. Certain eels with tiny eyes depend mostly on smell for location of food. The olfactory, or nasal, organ of fishes is located on the dorsal surface of the snout. The lining of the nasal organ has special sensory cells that perceive chemicals dissolved in the water, such as substances from food material, and send sensory information to the brain by way of the first cranial nerve. Odour also serves as an alarm system. Many fishes, especially various species of freshwater minnows, react with alarm to a chemical released from the skin of an injured member of their own species.
Many fishes have a well-developed sense of taste, and tiny pitlike taste buds or organs are located not only within their mouth cavities but also over their heads and parts of their body. Catfishes, which often have poor vision, have barbels (“whiskers”) that serve as supplementary taste organs, those around the mouth being actively used to search out food on the bottom. Some species of naturally blind cave fishes are especially well supplied with taste buds, which often cover most of their body surface.
Sight is extremely important in most fishes. The eye of a fish is basically like that of all other vertebrates, but the eyes of fishes are extremely varied in structure and adaptation. In general, fishes living in dark and dim water habitats have large eyes, unless they have specialized in some compensatory way so that another sense (such as smell) is dominant, in which case the eyes will often be reduced. Fishes living in brightly lighted shallow waters often will have relatively small but efficient eyes. Cyclostomes have somewhat less elaborate eyes than other fishes, with skin stretched over the eyeball perhaps making their vision somewhat less effective. Most fishes have a spherical lens and accommodate their vision to far or near subjects by moving the lens within the eyeball. A few sharks accommodate by changing the shape of the lens, as in land vertebrates. Those fishes that are heavily dependent upon the eyes have especially strong muscles for accommodation. Most fishes see well, despite the restrictions imposed by frequent turbidity of the water and by light refraction.
Fossil evidence suggests that colour vision evolved in fishes more than 300 million years ago, but not all living fishes have retained this ability. Experimental evidence indicates that many shallow-water fishes, if not all, have colour vision and see some colours especially well, but some bottom-dwelling shore fishes live in areas where the water is sufficiently deep to filter out most if not all colours, and these fishes apparently never see colours. When tested in shallow water, they apparently are unable to respond to colour differences.
Sound perception and balance are intimately associated senses in a fish. The organs of hearing are entirely internal, located within the skull, on each side of the brain and somewhat behind the eyes. Sound waves, especially those of low frequencies, travel readily through water and impinge directly upon the bones and fluids of the head and body, to be transmitted to the hearing organs. Fishes readily respond to sound; for example, a trout conditioned to escape by the approach of fishermen will take flight upon perceiving footsteps on a stream bank even if it cannot see a fisherman. Compared with humans, however, the range of sound frequencies heard by fishes is greatly restricted. Many fishes communicate with each other by producing sounds in their swim bladders, in their throats by rasping their teeth, and in other ways.
A fish or other vertebrate seldom has to rely on a single type of sensory information to determine the nature of the environment around it. A catfish uses taste and touch when examining a food object with its oral barbels. Like most other animals, fishes have many touch receptors over their body surface. Pain and temperature receptors also are present in fishes and presumably produce the same kind of information to a fish as to humans. Fishes react in a negative fashion to stimuli that would be painful to human beings, suggesting that they feel a sensation of pain.
An important sensory system in fishes that is absent in other vertebrates (except some amphibians) is the lateral line system. This consists of a series of heavily innervated small canals located in the skin and bone around the eyes, along the lower jaw, over the head, and down the mid-side of the body, where it is associated with the scales. Intermittently along these canals are located tiny sensory organs (pit organs) that apparently detect changes in pressure. The system allows a fish to sense changes in water currents and pressure, thereby helping the fish to orient itself to the various changes that occur in the physical environment.
Fish, any of approximately 34,000 species of vertebrate animals (phylum Chordata) found in the fresh and salt waters of the world. Living species range from the primitive jawless lampreys and hagfishes through the cartilaginous sharks, skates, and rays to the abundant and diverse bony fishes. Most fish species are cold-blooded; however, one species, the opah (Lampris guttatus), is warm-blooded.
The term fish is applied to a variety of vertebrates of several evolutionary lines. It describes a life-form rather than a taxonomic group. As members of the phylum Chordata, fish share certain features with other vertebrates. These features are gill slits at some point in the life cycle, a notochord, or skeletal supporting rod, a dorsal hollow nerve cord, and a tail. Living fishes represent some five classes, which are as distinct from one another as are the four classes of familiar air-breathing animals—amphibians, reptiles, birds, and mammals. For example, the jawless fishes (Agnatha) have gills in pouches and lack limb girdles. Extant agnathans are the lampreys and the hagfishes. As the name implies, the skeletons of fishes of the class Chondrichthyes (from chondr, “cartilage,” and ichthyes, “fish”) are made entirely of cartilage. Modern fish of this class lack a swim bladder, and their scales and teeth are made up of the same placoid material. Sharks, skates, and rays are examples of cartilaginous fishes. The bony fishes are by far the largest class. Examples range from the tiny seahorse to the 450-kg (1,000-pound) blue marlin, from the flattened soles and flounders to the boxy puffers and ocean sunfishes. Unlike the scales of the cartilaginous fishes, those of bony fishes, when present, grow throughout life and are made up of thin overlapping plates of bone. Bony fishes also have an operculum that covers the gill slits.
The study of fishes, the science of ichthyology, is of broad importance. Fishes are of interest to humans for many reasons, the most important being their relationship with and dependence on the environment. A more obvious reason for interest in fishes is their role as a moderate but important part of the world’s food supply. This resource, once thought unlimited, is now realized to be finite and in delicate balance with the biological, chemical, and physical factors of the aquatic environment. Overfishing, pollution, and alteration of the environment are the chief enemies of proper fisheries management, both in fresh waters and in the ocean. (For a detailed discussion of the technology and economics of fisheries, see commercial fishing.) Another practical reason for studying fishes is their use in disease control. As predators on mosquito larvae, they help curb malaria and other mosquito-borne diseases.
Fishes are valuable laboratory animals in many aspects of medical and biological research. For example, the readiness of many fishes to acclimate to captivity has allowed biologists to study behaviour, physiology, and even ecology under relatively natural conditions. Fishes have been especially important in the study of animal behaviour, where research on fishes has provided a broad base for the understanding of the more flexible behaviour of the higher vertebrates. The zebra fish is used as a model in studies of gene expression.
There are aesthetic and recreational reasons for an interest in fishes. Millions of people keep live fishes in home aquariums for the simple pleasure of observing the beauty and behaviour of animals otherwise unfamiliar to them. Aquarium fishes provide a personal challenge to many aquarists, allowing them to test their ability to keep a small section of the natural environment in their homes. Sportfishing is another way of enjoying the natural environment, also indulged in by millions of people every year. Interest in aquarium fishes and sportfishing supports multimillion-dollar industries throughout the world.
Fishes have been in existence for more than 450 million years, during which time they have evolved repeatedly to fit into almost every conceivable type of aquatic habitat. In a sense, land vertebrates are simply highly modified fishes: when fishes colonized the land habitat, they became tetrapod (four-legged) land vertebrates. The popular conception of a fish as a slippery, streamlined aquatic animal that possesses fins and breathes by gills applies to many fishes, but far more fishes deviate from that conception than conform to it. For example, the body is elongate in many forms and greatly shortened in others; the body is flattened in some (principally in bottom-dwelling fishes) and laterally compressed in many others; the fins may be elaborately extended, forming intricate shapes, or they may be reduced or even lost; and the positions of the mouth, eyes, nostrils, and gill openings vary widely. Air breathers have appeared in several evolutionary lines.
Many fishes are cryptically coloured and shaped, closely matching their respective environments; others are among the most brilliantly coloured of all organisms, with a wide range of hues, often of striking intensity, on a single individual. The brilliance of pigments may be enhanced by the surface structure of the fish, so that it almost seems to glow. A number of unrelated fishes have actual light-producing organs. Many fishes are able to alter their coloration—some for the purpose of camouflage, others for the enhancement of behavioral signals.
Fishes range in adult length from less than 10 mm (0.4 inch) to more than 20 metres (60 feet) and in weight from about 1.5 grams (less than 0.06 ounce) to many thousands of kilograms. Some live in shallow thermal springs at temperatures slightly above 42 °C (100 °F), others in cold Arctic seas a few degrees below 0 °C (32 °F) or in cold deep waters more than 4,000 metres (13,100 feet) beneath the ocean surface. The structural and, especially, the physiological adaptations for life at such extremes are relatively poorly known and provide the scientifically curious with great incentive for study.
Almost all natural bodies of water bear fish life, the exceptions being very hot thermal ponds and extremely salt-alkaline lakes, such as the Dead Sea in Asia and the Great Salt Lake in North America. The present distribution of fishes is a result of the geological history and development of Earth as well as the ability of fishes to undergo evolutionary change and to adapt to the available habitats. Fishes may be seen to be distributed according to habitat and according to geographical area. Major habitat differences are marine and freshwater. For the most part, the fishes in a marine habitat differ from those in a freshwater habitat, even in adjacent areas, but some, such as the salmon, migrate from one to the other. The freshwater habitats may be seen to be of many kinds. Fishes found in mountain torrents, Arctic lakes, tropical lakes, temperate streams, and tropical rivers will all differ from each other, both in obvious gross structure and in physiological attributes. Even in closely adjacent habitats where, for example, a tropical mountain torrent enters a lowland stream, the fish fauna will differ. The marine habitats can be divided into deep ocean floors (benthic), mid-water oceanic (bathypelagic), surface oceanic (pelagic), rocky coast, sandy coast, muddy shores, bays, estuaries, and others. Also, for example, rocky coastal shores in tropical and temperate regions will have different fish faunas, even when such habitats occur along the same coastline.
Although much is known about the present geographical distribution of fishes, far less is known about how that distribution came about. Many parts of the fish fauna of the fresh waters of North America and Eurasia are related and undoubtedly have a common origin. The faunas of Africa and South America are related, extremely old, and probably an expression of the drifting apart of the two continents. The fauna of southern Asia is related to that of Central Asia, and some of it appears to have entered Africa. The extremely large shore-fish faunas of the Indian and tropical Pacific oceans comprise a related complex, but the tropical shore fauna of the Atlantic, although containing Indo-Pacific components, is relatively limited and probably younger. The Arctic and Antarctic marine faunas are quite different from each other. The shore fauna of the North Pacific is quite distinct, and that of the North Atlantic more limited and probably younger. Pelagic oceanic fishes, especially those in deep waters, are similar the world over, showing little geographical isolation in terms of family groups. The deep oceanic habitat is very much the same throughout the world, but species differences do exist, showing geographical areas determined by oceanic currents and water masses.
All aspects of the life of a fish are closely correlated with adaptation to the total environment, physical, chemical, and biological. In studies, all the interdependent aspects of fish, such as behaviour, locomotion, reproduction, and physical and physiological characteristics, must be taken into account.
Correlated with their adaptation to an extremely wide variety of habitats is the extremely wide variety of life cycles that fishes display. The great majority hatch from relatively small eggs a few days to several weeks or more after the eggs are scattered in the water. Newly hatched young are still partially undeveloped and are called larvae until body structures such as fins, skeleton, and some organs are fully formed. Larval life is often very short, usually less than a few weeks, but it can be very long, some lampreys continuing as larvae for at least five years. Young and larval fishes, before reaching sexual maturity, must grow considerably, and their small size and other factors often dictate that they live in a habitat different than that of the adults. For example, most tropical marine shore fishes have pelagic larvae. Larval food also is different, and larval fishes often live in shallow waters, where they may be less exposed to predators.
After a fish reaches adult size, the length of its life is subject to many factors, such as innate rates of aging, predation pressure, and the nature of the local climate. The longevity of a species in the protected environment of an aquarium may have nothing to do with how long members of that species live in the wild. Many small fishes live only one to three years at the most. In some species, however, individuals may live as long as 10 or 20 or even 100 years.
Fish behaviour is a complicated and varied subject. As in almost all animals with a central nervous system, the nature of a response of an individual fish to stimuli from its environment depends upon the inherited characteristics of its nervous system, on what it has learned from past experience, and on the nature of the stimuli. Compared with the variety of human responses, however, that of a fish is stereotyped, not subject to much modification by “thought” or learning, and investigators must guard against anthropomorphic interpretations of fish behaviour.
Fishes perceive the world around them by the usual senses of sight, smell, hearing, touch, and taste and by special lateral line water-current detectors. In the few fishes that generate electric fields, a process that might best be called electrolocation aids in perception. One or another of these senses often is emphasized at the expense of others, depending upon the fish’s other adaptations. In fishes with large eyes, the sense of smell may be reduced; others, with small eyes, hunt and feed primarily by smell (such as some eels).
Specialized behaviour is primarily concerned with the three most important activities in the fish’s life: feeding, reproduction, and escape from enemies. Schooling behaviour of sardines on the high seas, for instance, is largely a protective device to avoid enemies, but it is also associated with and modified by their breeding and feeding requirements. Predatory fishes are often solitary, lying in wait to dart suddenly after their prey, a kind of locomotion impossible for beaked parrot fishes, which feed on coral, swimming in small groups from one coral head to the next. In addition, some predatory fishes that inhabit pelagic environments, such as tunas, often school.
Sleep in fishes, all of which lack true eyelids, consists of a seemingly listless state in which the fish maintains its balance but moves slowly. If attacked or disturbed, most can dart away. A few kinds of fishes lie on the bottom to sleep. Most catfishes, some loaches, and some eels and electric fishes are strictly nocturnal, being active and hunting for food during the night and retiring during the day to holes, thick vegetation, or other protective parts of the environment.
Communication between members of a species or between members of two or more species often is extremely important, especially in breeding behaviour (see below Reproduction). The mode of communication may be visual, as between the small so-called cleaner fish and a large fish of a very different species. The larger fish often allows the cleaner to enter its mouth to remove gill parasites. The cleaner is recognized by its distinctive colour and actions and therefore is not eaten, even if the larger fish is normally a predator. Communication is often chemical, signals being sent by specific chemicals called pheromones.
Many fishes have a streamlined body and swim freely in open water. Fish locomotion is closely correlated with habitat and ecological niche (the general position of the animal to its environment).
Many fishes in both marine and fresh waters swim at the surface and have mouths adapted to feed best (and sometimes only) at the surface. Often such fishes are long and slender, able to dart at surface insects or at other surface fishes and in turn to dart away from predators; needlefishes, halfbeaks, and topminnows (such as killifish and mosquito fish) are good examples. Oceanic flying fishes escape their predators by gathering speed above the water surface, with the lower lobe of the tail providing thrust in the water. They then glide hundreds of yards on enlarged, winglike pectoral and pelvic fins. South American freshwater flying fishes escape their enemies by jumping and propelling their strongly keeled bodies out of the water.
So-called mid-water swimmers, the most common type of fish, are of many kinds and live in many habitats. The powerful fusiform tunas and the trouts, for example, are adapted for strong, fast swimming, the tunas to capture prey speedily in the open ocean and the trouts to cope with the swift currents of streams and rivers. The trout body form is well adapted to many habitats. Fishes that live in relatively quiet waters such as bays or lake shores or slow rivers usually are not strong, fast swimmers but are capable of short, quick bursts of speed to escape a predator. Many of these fishes have their sides flattened, examples being the sunfish and the freshwater angelfish of aquarists. Fish associated with the bottom or substrate usually are slow swimmers. Open-water plankton-feeding fishes almost always remain fusiform and are capable of rapid, strong movement (for example, sardines and herrings of the open ocean and also many small minnows of streams and lakes).
Bottom-living fishes are of many kinds and have undergone many types of modification of their body shape and swimming habits. Rays, which evolved from strong-swimming mid-water sharks, usually stay close to the bottom and move by undulating their large pectoral fins. Flounders live in a similar habitat and move over the bottom by undulating the entire body. Many bottom fishes dart from place to place, resting on the bottom between movements, a motion common in gobies. One goby relative, the mudskipper, has taken to living at the edge of pools along the shore of muddy mangrove swamps. It escapes its enemies by flipping rapidly over the mud, out of the water. Some catfishes, synbranchid eels, the so-called climbing perch, and a few other fishes venture out over damp ground to find more promising waters than those that they left. They move by wriggling their bodies, sometimes using strong pectoral fins; most have accessory air-breathing organs. Many bottom-dwelling fishes live in mud holes or rocky crevices. Marine eels and gobies commonly are found in such habitats and for the most part venture far beyond their cavelike homes. Some bottom dwellers, such as the clingfishes (Gobiesocidae), have developed powerful adhesive disks that enable them to remain in place on the substrate in areas such as rocky coasts, where the action of the waves is great.
The methods of reproduction in fishes are varied, but most fishes lay a large number of small eggs, fertilized and scattered outside of the body. The eggs of pelagic fishes usually remain suspended in the open water. Many shore and freshwater fishes lay eggs on the bottom or among plants. Some have adhesive eggs. The mortality of the young and especially of the eggs is very high, and often only a few individuals grow to maturity out of hundreds, thousands, and in some cases millions of eggs laid.
Males produce sperm, usually as a milky white substance called milt, in two (sometimes one) testes within the body cavity. In bony fishes a sperm duct leads from each testis to a urogenital opening behind the vent or anus. In sharks and rays and in cyclostomes the duct leads to a cloaca. Sometimes the pelvic fins are modified to help transmit the milt to the eggs at the female’s vent or on the substrate where the female has placed them. Sometimes accessory organs are used to fertilize females internally—for example, the claspers of many sharks and rays.
In the females the eggs are formed in two ovaries (sometimes only one) and pass through the ovaries to the urogenital opening and to the outside. In some fishes the eggs are fertilized internally but are shed before development takes place. Members of about a dozen families each of bony fishes (teleosts) and sharks bear live young. Many skates and rays also bear live young. In some bony fishes the eggs simply develop within the female, the young emerging when the eggs hatch (ovoviviparous). Others develop within the ovary and are nourished by ovarian tissues after hatching (viviparous). There are also other methods utilized by fishes to nourish young within the female. In all live-bearers the young are born at a relatively large size and are few in number. In one family of primarily marine fishes, the surfperches from the Pacific coast of North America, Japan, and Korea, the males of at least one species are born sexually mature, although they are not fully grown.
Some fishes are hermaphroditic—an individual producing both sperm and eggs, usually at different stages of its life. Self-fertilization, however, is probably rare.
Successful reproduction and, in many cases, defense of the eggs and the young are assured by rather stereotypical but often elaborate courtship and parental behaviour, either by the male or the female or both. Some fishes prepare nests by hollowing out depressions in the sand bottom (cichlids, for example), build nests with plant materials and sticky threads excreted by the kidneys (sticklebacks), or blow a cluster of mucus-covered bubbles at the water surface (gouramis). The eggs are laid in these structures. Some varieties of cichlids and catfishes incubate eggs in their mouths.
Some fishes, such as salmon, undergo long migrations from the ocean and up large rivers to spawn in the gravel beds where they themselves hatched (anadromous fishes). Some, such as the freshwater eels (family Anguillidae), live and grow to maturity in fresh water and migrate to the sea to spawn (catadromous fishes). Other fishes undertake shorter migrations from lakes into streams, within the ocean, or enter spawning habitats that they do not ordinarily occupy in other ways.
The basic structure and function of the fish body are similar to those of all other vertebrates. The usual four types of tissues are present: surface or epithelial, connective (bone, cartilage, and fibrous tissues, as well as their derivative, blood), nerve, and muscle tissues. In addition, the fish’s organs and organ systems parallel those of other vertebrates.
The typical fish body is streamlined and spindle-shaped, with an anterior head, a gill apparatus, and a heart, the latter lying in the midline just below the gill chamber. The body cavity, containing the vital organs, is situated behind the head in the lower anterior part of the body. The anus usually marks the posterior termination of the body cavity and most often occurs just in front of the base of the anal fin. The spinal cord and vertebral column continue from the posterior part of the head to the base of the tail fin, passing dorsal to the body cavity and through the caudal (tail) region behind the body cavity. Most of the body is of muscular tissue, a high proportion of which is necessitated by swimming. In the course of evolution this basic body plan has been modified repeatedly into the many varieties of fish shapes that exist today.
The skeleton forms an integral part of the fish’s locomotion system, as well as serving to protect vital parts. The internal skeleton consists of the skull bones (except for the roofing bones of the head, which are really part of the external skeleton), the vertebral column, and the fin supports (fin rays). The fin supports are derived from the external skeleton but will be treated here because of their close functional relationship to the internal skeleton. The internal skeleton of cyclostomes, sharks, and rays is of cartilage; that of many fossil groups and some primitive living fishes is mostly of cartilage but may include some bone. In place of the vertebral column, the earliest vertebrates had a fully developed notochord, a flexible stiff rod of viscous cells surrounded by a strong fibrous sheath. During the evolution of modern fishes the rod was replaced in part by cartilage and then by ossified cartilage. Sharks and rays retain a cartilaginous vertebral column; bony fishes have spool-shaped vertebrae that in the more primitive living forms only partially replace the notochord. The skull, including the gill arches and jaws of bony fishes, is fully, or at least partially, ossified. That of sharks and rays remains cartilaginous, at times partially replaced by calcium deposits but never by true bone.
The supportive elements of the fins (basal or radial bones or both) have changed greatly during fish evolution. Some of these changes are described in the section below (Evolution and paleontology). Most fishes possess a single dorsal fin on the midline of the back. Many have two and a few have three dorsal fins. The other fins are the single tail and anal fins and paired pelvic and pectoral fins. A small fin, the adipose fin, with hairlike fin rays, occurs in many of the relatively primitive teleosts (such as trout) on the back near the base of the caudal fin.
The skin of a fish must serve many functions. It aids in maintaining the osmotic balance, provides physical protection for the body, is the site of coloration, contains sensory receptors, and, in some fishes, functions in respiration. Mucous glands, which aid in maintaining the water balance and offer protection from bacteria, are extremely numerous in fish skin, especially in cyclostomes and teleosts. Since mucous glands are present in the modern lampreys, it is reasonable to assume that they were present in primitive fishes, such as the ancient Silurian and Devonian agnathans. Protection from abrasion and predation is another function of the fish skin, and dermal (skin) bone arose early in fish evolution in response to this need. It is thought that bone first evolved in skin and only later invaded the cartilaginous areas of the fish’s body, to provide additional support and protection. There is some argument as to which came first, cartilage or bone, and fossil evidence does not settle the question. In any event, dermal bone has played an important part in fish evolution and has different characteristics in different groups of fishes. Several groups are characterized at least in part by the kind of bony scales they possess.
Scales have played an important part in the evolution of fishes. Primitive fishes usually had thick bony plates or thick scales in several layers of bone, enamel, and related substances. Modern teleost fishes have scales of bone, which, while still protective, allow much more freedom of motion in the body. A few modern teleosts (some catfishes, sticklebacks, and others) have secondarily acquired bony plates in the skin. Modern and early sharks possessed placoid scales, a relatively primitive type of scale with a toothlike structure, consisting of an outside layer of enamel-like substance (vitrodentine), an inner layer of dentine, and a pulp cavity containing nerves and blood vessels. Primitive bony fishes had thick scales of either the ganoid or the cosmoid type. Cosmoid scales have a hard, enamel-like outer layer, an inner layer of cosmine (a form of dentine), and then a layer of vascular bone (isopedine). In ganoid scales the hard outer layer is different chemically and is called ganoin. Under this is a cosminelike layer and then a vascular bony layer. The thin, translucent bony scales of modern fishes, called cycloid and ctenoid (the latter distinguished by serrations at the edges), lack enameloid and dentine layers.
Skin has several other functions in fishes. It is well supplied with nerve endings and presumably receives tactile, thermal, and pain stimuli. Skin is also well supplied with blood vessels. Some fishes breathe in part through the skin, by the exchange of oxygen and carbon dioxide between the surrounding water and numerous small blood vessels near the skin surface.
Skin serves as protection through the control of coloration. Fishes exhibit an almost limitless range of colours. The colours often blend closely with the surroundings, effectively hiding the animal. Many fishes use bright colours for territorial advertisement or as recognition marks for other members of their own species, or sometimes for members of other species. Many fishes can change their colour to a greater or lesser degree, by movement of pigment within the pigment cells (chromatophores). Black pigment cells (melanophores), of almost universal occurrence in fishes, are often juxtaposed with other pigment cells. When placed beneath iridocytes or leucophores (bearing the silvery or white pigment guanine), melanophores produce structural colours of blue and green. These colours are often extremely intense, because they are formed by refraction of light through the needlelike crystals of guanine. The blue and green refracted colours are often relatively pure, lacking the red and yellow rays, which have been absorbed by the black pigment (melanin) of the melanophores. Yellow, orange, and red colours are produced by erythrophores, cells containing the appropriate carotenoid pigments. Other colours are produced by combinations of melanophores, erythrophores, and iridocytes.
The major portion of the body of most fishes consists of muscles. Most of the mass is trunk musculature, the fin muscles usually being relatively small. The caudal fin is usually the most powerful fin, being moved by the trunk musculature. The body musculature is usually arranged in rows of chevron-shaped segments on each side. Contractions of these segments, each attached to adjacent vertebrae and vertebral processes, bends the body on the vertebral joint, producing successive undulations of the body, passing from the head to the tail, and producing driving strokes of the tail. It is the latter that provides the strong forward movement for most fishes.
The digestive system, in a functional sense, starts at the mouth, with the teeth used to capture prey or collect plant foods. Mouth shape and tooth structure vary greatly in fishes, depending on the kind of food normally eaten. Most fishes are predacious, feeding on small invertebrates or other fishes and have simple conical teeth on the jaws, on at least some of the bones of the roof of the mouth, and on special gill arch structures just in front of the esophagus. The latter are throat teeth. Most predacious fishes swallow their prey whole, and the teeth are used for grasping and holding prey, for orienting prey to be swallowed (head first) and for working the prey toward the esophagus. There are a variety of tooth types in fishes. Some fishes, such as sharks and piranhas, have cutting teeth for biting chunks out of their victims. A shark’s tooth, although superficially like that of a piranha, appears in many respects to be a modified scale, while that of the piranha is like that of other bony fishes, consisting of dentine and enamel. Parrot fishes have beaklike mouths with short incisor-like teeth for breaking off coral and have heavy pavementlike throat teeth for crushing the coral. Some catfishes have small brushlike teeth, arranged in rows on the jaws, for scraping plant and animal growth from rocks. Many fishes (such as the Cyprinidae or minnows) have no jaw teeth at all but have very strong throat teeth.
Some fishes gather planktonic food by straining it from their gill cavities with numerous elongate stiff rods (gill rakers) anchored by one end to the gill bars. The food collected on these rods is passed to the throat, where it is swallowed. Most fishes have only short gill rakers that help keep food particles from escaping out the mouth cavity into the gill chamber.
Once reaching the throat, food enters a short, often greatly distensible esophagus, a simple tube with a muscular wall leading into a stomach. The stomach varies greatly in fishes, depending upon the diet. In most predacious fishes it is a simple straight or curved tube or pouch with a muscular wall and a glandular lining. Food is largely digested there and leaves the stomach in liquid form.
Between the stomach and the intestine, ducts enter the digestive tube from the liver and pancreas. The liver is a large, clearly defined organ. The pancreas may be embedded in it, diffused through it, or broken into small parts spread along some of the intestine. The junction between the stomach and the intestine is marked by a muscular valve. Pyloric ceca (blind sacs) occur in some fishes at this junction and have a digestive or absorptive function or both.
The intestine itself is quite variable in length, depending upon the fish’s diet. It is short in predacious forms, sometimes no longer than the body cavity, but long in herbivorous forms, being coiled and several times longer than the entire length of the fish in some species of South American catfishes. The intestine is primarily an organ for absorbing nutrients into the bloodstream. The larger its internal surface, the greater its absorptive efficiency, and a spiral valve is one method of increasing its absorption surface.
Sharks, rays, chimaeras, lungfishes, surviving chondrosteans, holosteans, and even a few of the more primitive teleosts have a spiral valve or at least traces of it in the intestine. Most modern teleosts have increased the area of the intestinal walls by having numerous folds and villi (fingerlike projections) somewhat like those in humans. Undigested substances are passed to the exterior through the anus in most teleost fishes. In lungfishes, sharks, and rays, it is first passed through the cloaca, a common cavity receiving the intestinal opening and the ducts from the urogenital system.
Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills. The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour. Water taken in continuously through the mouth passes backward between the gill bars and over the gill filaments, where the exchange of gases takes place. The gills are protected by a gill cover in teleosts and many other fishes but by flaps of skin in sharks, rays, and some of the older fossil fish groups. The blood capillaries in the gill filaments are close to the gill surface to take up oxygen from the water and to give up excess carbon dioxide to the water.
Most modern fishes have a hydrostatic (ballast) organ, called the swim bladder, that lies in the body cavity just below the kidney and above the stomach and intestine. It originated as a diverticulum of the digestive canal. In advanced teleosts, especially the acanthopterygians, the bladder has lost its connection with the digestive tract, a condition called physoclistic. The connection has been retained (physostomous) by many relatively primitive teleosts. In several unrelated lines of fishes, the bladder has become specialized as a lung or, at least, as a highly vascularized accessory breathing organ. Some fishes with such accessory organs are obligate air breathers and will drown if denied access to the surface, even in well-oxygenated water. Fishes with a hydrostatic form of swim bladder can control their depth by regulating the amount of gas in the bladder. The gas, mostly oxygen, is secreted into the bladder by special glands, rendering the fish more buoyant; the gas is absorbed into the bloodstream by another special organ, reducing the overall buoyancy and allowing the fish to sink. Some deep-sea fishes may have oils, rather than gas, in the bladder. Other deep-sea and some bottom-living forms have much-reduced swim bladders or have lost the organ entirely.
The swim bladder of fishes follows the same developmental pattern as the lungs of land vertebrates. There is no doubt that the two structures have the same historical origin in primitive fishes. More or less intermediate forms still survive among the more primitive types of fishes, such as the lungfishes Lepidosiren and Protopterus.
The circulatory, or blood vascular, system consists of the heart, the arteries, the capillaries, and the veins. It is in the capillaries that the interchange of oxygen, carbon dioxide, nutrients, and other substances such as hormones and waste products takes place. The capillaries lead to the veins, which return the venous blood with its waste products to the heart, kidneys, and gills. There are two kinds of capillary beds: those in the gills and those in the rest of the body. The heart, a folded continuous muscular tube with three or four saclike enlargements, undergoes rhythmic contractions and receives venous blood in a sinus venosus. It passes the blood to an auricle and then into a thick muscular pump, the ventricle. From the ventricle the blood goes to a bulbous structure at the base of a ventral aorta just below the gills. The blood passes to the afferent (receiving) arteries of the gill arches and then to the gill capillaries. There waste gases are given off to the environment, and oxygen is absorbed. The oxygenated blood enters efferent (exuant) arteries of the gill arches and then flows into the dorsal aorta. From there blood is distributed to the tissues and organs of the body. One-way valves prevent backflow. The circulation of fishes thus differs from that of the reptiles, birds, and mammals in that oxygenated blood is not returned to the heart prior to distribution to the other parts of the body.
The primary excretory organ in fishes, as in other vertebrates, is the kidney. In fishes some excretion also takes place in the digestive tract, skin, and especially the gills (where ammonia is given off). Compared with land vertebrates, fishes have a special problem in maintaining their internal environment at a constant concentration of water and dissolved substances, such as salts. Proper balance of the internal environment (homeostasis) of a fish is in a great part maintained by the excretory system, especially the kidney.
The kidney, gills, and skin play an important role in maintaining a fish’s internal environment and checking the effects of osmosis. Marine fishes live in an environment in which the water around them has a greater concentration of salts than they can have inside their body and still maintain life. Freshwater fishes, on the other hand, live in water with a much lower concentration of salts than they require inside their bodies. Osmosis tends to promote the loss of water from the body of a marine fish and absorption of water by that of a freshwater fish. Mucus in the skin tends to slow the process but is not a sufficient barrier to prevent the movement of fluids through the permeable skin. When solutions on two sides of a permeable membrane have different concentrations of dissolved substances, water will pass through the membrane into the more concentrated solution, while the dissolved chemicals move into the area of lower concentration (diffusion).
The kidney of freshwater fishes is often larger in relation to body weight than that of marine fishes. In both groups the kidney excretes wastes from the body, but the kidney of freshwater fishes also excretes large amounts of water, counteracting the water absorbed through the skin. Freshwater fishes tend to lose salt to the environment and must replace it. They get some salt from their food, but the gills and skin inside the mouth actively absorb salt from water passed through the mouth. This absorption is performed by special cells capable of moving salts against the diffusion gradient. Freshwater fishes drink very little water and take in little water with their food.
Marine fishes must conserve water, and therefore their kidneys excrete little water. To maintain their water balance, marine fishes drink large quantities of seawater, retaining most of the water and excreting the salt. Most nitrogenous waste in marine fishes appears to be secreted by the gills as ammonia. Marine fishes can excrete salt by clusters of special cells (chloride cells) in the gills.
There are several teleosts—for example, the salmon—that travel between fresh water and seawater and must adjust to the reversal of osmotic gradients. They adjust their physiological processes by spending time (often surprisingly little time) in the intermediate brackish environment.
Marine hagfishes, sharks, and rays have osmotic concentrations in their blood about equal to that of seawater and so do not have to drink water nor perform much physiological work to maintain their osmotic balance. In sharks and rays the osmotic concentration is kept high by retention of urea in the blood. Freshwater sharks have a lowered concentration of urea in the blood.
Endocrine glands secrete their products into the bloodstream and body tissues and, along with the central nervous system, control and regulate many kinds of body functions. Cyclostomes have a well-developed endocrine system, and presumably it was well developed in the early Agnatha, ancestral to modern fishes. Although the endocrine system in fishes is similar to that of higher vertebrates, there are numerous differences in detail. The pituitary, the thyroid, the suprarenals, the adrenals, the pancreatic islets, the sex glands (ovaries and testes), the inner wall of the intestine, and the bodies of the ultimobranchial gland make up the endocrine system in fishes. There are some others whose function is not well understood. These organs regulate sexual activity and reproduction, growth, osmotic pressure, general metabolic activities such as the storage of fat and the utilization of foodstuffs, blood pressure, and certain aspects of skin colour. Many of these activities are also controlled in part by the central nervous system, which works with the endocrine system in maintaining the life of a fish. Some parts of the endocrine system are developmentally, and undoubtedly evolutionarily, derived from the nervous system.
As in all vertebrates, the nervous system of fishes is the primary mechanism coordinating body activities, as well as integrating these activities in the appropriate manner with stimuli from the environment. The central nervous system, consisting of the brain and spinal cord, is the primary integrating mechanism. The peripheral nervous system, consisting of nerves that connect the brain and spinal cord to various body organs, carries sensory information from special receptor organs such as the eyes, internal ears, nares (sense of smell), taste glands, and others to the integrating centres of the brain and spinal cord. The peripheral nervous system also carries information via different nerve cells from the integrating centres of the brain and spinal cord. This coded information is carried to the various organs and body systems, such as the skeletal muscular system, for appropriate action in response to the original external or internal stimulus. Another branch of the nervous system, the autonomic nervous system, helps to coordinate the activities of many glands and organs and is itself closely connected to the integrating centres of the brain.
The brain of the fish is divided into several anatomical and functional parts, all closely interconnected but each serving as the primary centre of integrating particular kinds of responses and activities. Several of these centres or parts are primarily associated with one type of sensory perception, such as sight, hearing, or smell (olfaction).
The sense of smell is important in almost all fishes. Certain eels with tiny eyes depend mostly on smell for location of food. The olfactory, or nasal, organ of fishes is located on the dorsal surface of the snout. The lining of the nasal organ has special sensory cells that perceive chemicals dissolved in the water, such as substances from food material, and send sensory information to the brain by way of the first cranial nerve. Odour also serves as an alarm system. Many fishes, especially various species of freshwater minnows, react with alarm to a chemical released from the skin of an injured member of their own species.
Many fishes have a well-developed sense of taste, and tiny pitlike taste buds or organs are located not only within their mouth cavities but also over their heads and parts of their body. Catfishes, which often have poor vision, have barbels (“whiskers”) that serve as supplementary taste organs, those around the mouth being actively used to search out food on the bottom. Some species of naturally blind cave fishes are especially well supplied with taste buds, which often cover most of their body surface.
Sight is extremely important in most fishes. The eye of a fish is basically like that of all other vertebrates, but the eyes of fishes are extremely varied in structure and adaptation. In general, fishes living in dark and dim water habitats have large eyes, unless they have specialized in some compensatory way so that another sense (such as smell) is dominant, in which case the eyes will often be reduced. Fishes living in brightly lighted shallow waters often will have relatively small but efficient eyes. Cyclostomes have somewhat less elaborate eyes than other fishes, with skin stretched over the eyeball perhaps making their vision somewhat less effective. Most fishes have a spherical lens and accommodate their vision to far or near subjects by moving the lens within the eyeball. A few sharks accommodate by changing the shape of the lens, as in land vertebrates. Those fishes that are heavily dependent upon the eyes have especially strong muscles for accommodation. Most fishes see well, despite the restrictions imposed by frequent turbidity of the water and by light refraction.
Fossil evidence suggests that colour vision evolved in fishes more than 300 million years ago, but not all living fishes have retained this ability. Experimental evidence indicates that many shallow-water fishes, if not all, have colour vision and see some colours especially well, but some bottom-dwelling shore fishes live in areas where the water is sufficiently deep to filter out most if not all colours, and these fishes apparently never see colours. When tested in shallow water, they apparently are unable to respond to colour differences.
Sound perception and balance are intimately associated senses in a fish. The organs of hearing are entirely internal, located within the skull, on each side of the brain and somewhat behind the eyes. Sound waves, especially those of low frequencies, travel readily through water and impinge directly upon the bones and fluids of the head and body, to be transmitted to the hearing organs. Fishes readily respond to sound; for example, a trout conditioned to escape by the approach of fishermen will take flight upon perceiving footsteps on a stream bank even if it cannot see a fisherman. Compared with humans, however, the range of sound frequencies heard by fishes is greatly restricted. Many fishes communicate with each other by producing sounds in their swim bladders, in their throats by rasping their teeth, and in other ways.
A fish or other vertebrate seldom has to rely on a single type of sensory information to determine the nature of the environment around it. A catfish uses taste and touch when examining a food object with its oral barbels. Like most other animals, fishes have many touch receptors over their body surface. Pain and temperature receptors also are present in fishes and presumably produce the same kind of information to a fish as to humans. Fishes react in a negative fashion to stimuli that would be painful to human beings, suggesting that they feel a sensation of pain.
An important sensory system in fishes that is absent in other vertebrates (except some amphibians) is the lateral line system. This consists of a series of heavily innervated small canals located in the skin and bone around the eyes, along the lower jaw, over the head, and down the mid-side of the body, where it is associated with the scales. Intermittently along these canals are located tiny sensory organs (pit organs) that apparently detect changes in pressure. The system allows a fish to sense changes in water currents and pressure, thereby helping the fish to orient itself to the various changes that occur in the physical environment.
Fish, any of approximately 34,000 species of vertebrate animals (phylum Chordata) found in the fresh and salt waters of the world. Living species range from the primitive jawless lampreys and hagfishes through the cartilaginous sharks, skates, and rays to the abundant and diverse bony fishes. Most fish species are cold-blooded; however, one species, the opah (Lampris guttatus), is warm-blooded.
The term fish is applied to a variety of vertebrates of several evolutionary lines. It describes a life-form rather than a taxonomic group. As members of the phylum Chordata, fish share certain features with other vertebrates. These features are gill slits at some point in the life cycle, a notochord, or skeletal supporting rod, a dorsal hollow nerve cord, and a tail. Living fishes represent some five classes, which are as distinct from one another as are the four classes of familiar air-breathing animals—amphibians, reptiles, birds, and mammals. For example, the jawless fishes (Agnatha) have gills in pouches and lack limb girdles. Extant agnathans are the lampreys and the hagfishes. As the name implies, the skeletons of fishes of the class Chondrichthyes (from chondr, “cartilage,” and ichthyes, “fish”) are made entirely of cartilage. Modern fish of this class lack a swim bladder, and their scales and teeth are made up of the same placoid material. Sharks, skates, and rays are examples of cartilaginous fishes. The bony fishes are by far the largest class. Examples range from the tiny seahorse to the 450-kg (1,000-pound) blue marlin, from the flattened soles and flounders to the boxy puffers and ocean sunfishes. Unlike the scales of the cartilaginous fishes, those of bony fishes, when present, grow throughout life and are made up of thin overlapping plates of bone. Bony fishes also have an operculum that covers the gill slits.
The study of fishes, the science of ichthyology, is of broad importance. Fishes are of interest to humans for many reasons, the most important being their relationship with and dependence on the environment. A more obvious reason for interest in fishes is their role as a moderate but important part of the world’s food supply. This resource, once thought unlimited, is now realized to be finite and in delicate balance with the biological, chemical, and physical factors of the aquatic environment. Overfishing, pollution, and alteration of the environment are the chief enemies of proper fisheries management, both in fresh waters and in the ocean. (For a detailed discussion of the technology and economics of fisheries, see commercial fishing.) Another practical reason for studying fishes is their use in disease control. As predators on mosquito larvae, they help curb malaria and other mosquito-borne diseases.
Fishes are valuable laboratory animals in many aspects of medical and biological research. For example, the readiness of many fishes to acclimate to captivity has allowed biologists to study behaviour, physiology, and even ecology under relatively natural conditions. Fishes have been especially important in the study of animal behaviour, where research on fishes has provided a broad base for the understanding of the more flexible behaviour of the higher vertebrates. The zebra fish is used as a model in studies of gene expression.
There are aesthetic and recreational reasons for an interest in fishes. Millions of people keep live fishes in home aquariums for the simple pleasure of observing the beauty and behaviour of animals otherwise unfamiliar to them. Aquarium fishes provide a personal challenge to many aquarists, allowing them to test their ability to keep a small section of the natural environment in their homes. Sportfishing is another way of enjoying the natural environment, also indulged in by millions of people every year. Interest in aquarium fishes and sportfishing supports multimillion-dollar industries throughout the world.
Fishes have been in existence for more than 450 million years, during which time they have evolved repeatedly to fit into almost every conceivable type of aquatic habitat. In a sense, land vertebrates are simply highly modified fishes: when fishes colonized the land habitat, they became tetrapod (four-legged) land vertebrates. The popular conception of a fish as a slippery, streamlined aquatic animal that possesses fins and breathes by gills applies to many fishes, but far more fishes deviate from that conception than conform to it. For example, the body is elongate in many forms and greatly shortened in others; the body is flattened in some (principally in bottom-dwelling fishes) and laterally compressed in many others; the fins may be elaborately extended, forming intricate shapes, or they may be reduced or even lost; and the positions of the mouth, eyes, nostrils, and gill openings vary widely. Air breathers have appeared in several evolutionary lines.
Many fishes are cryptically coloured and shaped, closely matching their respective environments; others are among the most brilliantly coloured of all organisms, with a wide range of hues, often of striking intensity, on a single individual. The brilliance of pigments may be enhanced by the surface structure of the fish, so that it almost seems to glow. A number of unrelated fishes have actual light-producing organs. Many fishes are able to alter their coloration—some for the purpose of camouflage, others for the enhancement of behavioral signals.
Fishes range in adult length from less than 10 mm (0.4 inch) to more than 20 metres (60 feet) and in weight from about 1.5 grams (less than 0.06 ounce) to many thousands of kilograms. Some live in shallow thermal springs at temperatures slightly above 42 °C (100 °F), others in cold Arctic seas a few degrees below 0 °C (32 °F) or in cold deep waters more than 4,000 metres (13,100 feet) beneath the ocean surface. The structural and, especially, the physiological adaptations for life at such extremes are relatively poorly known and provide the scientifically curious with great incentive for study.
Almost all natural bodies of water bear fish life, the exceptions being very hot thermal ponds and extremely salt-alkaline lakes, such as the Dead Sea in Asia and the Great Salt Lake in North America. The present distribution of fishes is a result of the geological history and development of Earth as well as the ability of fishes to undergo evolutionary change and to adapt to the available habitats. Fishes may be seen to be distributed according to habitat and according to geographical area. Major habitat differences are marine and freshwater. For the most part, the fishes in a marine habitat differ from those in a freshwater habitat, even in adjacent areas, but some, such as the salmon, migrate from one to the other. The freshwater habitats may be seen to be of many kinds. Fishes found in mountain torrents, Arctic lakes, tropical lakes, temperate streams, and tropical rivers will all differ from each other, both in obvious gross structure and in physiological attributes. Even in closely adjacent habitats where, for example, a tropical mountain torrent enters a lowland stream, the fish fauna will differ. The marine habitats can be divided into deep ocean floors (benthic), mid-water oceanic (bathypelagic), surface oceanic (pelagic), rocky coast, sandy coast, muddy shores, bays, estuaries, and others. Also, for example, rocky coastal shores in tropical and temperate regions will have different fish faunas, even when such habitats occur along the same coastline.
Although much is known about the present geographical distribution of fishes, far less is known about how that distribution came about. Many parts of the fish fauna of the fresh waters of North America and Eurasia are related and undoubtedly have a common origin. The faunas of Africa and South America are related, extremely old, and probably an expression of the drifting apart of the two continents. The fauna of southern Asia is related to that of Central Asia, and some of it appears to have entered Africa. The extremely large shore-fish faunas of the Indian and tropical Pacific oceans comprise a related complex, but the tropical shore fauna of the Atlantic, although containing Indo-Pacific components, is relatively limited and probably younger. The Arctic and Antarctic marine faunas are quite different from each other. The shore fauna of the North Pacific is quite distinct, and that of the North Atlantic more limited and probably younger. Pelagic oceanic fishes, especially those in deep waters, are similar the world over, showing little geographical isolation in terms of family groups. The deep oceanic habitat is very much the same throughout the world, but species differences do exist, showing geographical areas determined by oceanic currents and water masses.
All aspects of the life of a fish are closely correlated with adaptation to the total environment, physical, chemical, and biological. In studies, all the interdependent aspects of fish, such as behaviour, locomotion, reproduction, and physical and physiological characteristics, must be taken into account.
Correlated with their adaptation to an extremely wide variety of habitats is the extremely wide variety of life cycles that fishes display. The great majority hatch from relatively small eggs a few days to several weeks or more after the eggs are scattered in the water. Newly hatched young are still partially undeveloped and are called larvae until body structures such as fins, skeleton, and some organs are fully formed. Larval life is often very short, usually less than a few weeks, but it can be very long, some lampreys continuing as larvae for at least five years. Young and larval fishes, before reaching sexual maturity, must grow considerably, and their small size and other factors often dictate that they live in a habitat different than that of the adults. For example, most tropical marine shore fishes have pelagic larvae. Larval food also is different, and larval fishes often live in shallow waters, where they may be less exposed to predators.
After a fish reaches adult size, the length of its life is subject to many factors, such as innate rates of aging, predation pressure, and the nature of the local climate. The longevity of a species in the protected environment of an aquarium may have nothing to do with how long members of that species live in the wild. Many small fishes live only one to three years at the most. In some species, however, individuals may live as long as 10 or 20 or even 100 years.
Fish behaviour is a complicated and varied subject. As in almost all animals with a central nervous system, the nature of a response of an individual fish to stimuli from its environment depends upon the inherited characteristics of its nervous system, on what it has learned from past experience, and on the nature of the stimuli. Compared with the variety of human responses, however, that of a fish is stereotyped, not subject to much modification by “thought” or learning, and investigators must guard against anthropomorphic interpretations of fish behaviour.
Fishes perceive the world around them by the usual senses of sight, smell, hearing, touch, and taste and by special lateral line water-current detectors. In the few fishes that generate electric fields, a process that might best be called electrolocation aids in perception. One or another of these senses often is emphasized at the expense of others, depending upon the fish’s other adaptations. In fishes with large eyes, the sense of smell may be reduced; others, with small eyes, hunt and feed primarily by smell (such as some eels).
Specialized behaviour is primarily concerned with the three most important activities in the fish’s life: feeding, reproduction, and escape from enemies. Schooling behaviour of sardines on the high seas, for instance, is largely a protective device to avoid enemies, but it is also associated with and modified by their breeding and feeding requirements. Predatory fishes are often solitary, lying in wait to dart suddenly after their prey, a kind of locomotion impossible for beaked parrot fishes, which feed on coral, swimming in small groups from one coral head to the next. In addition, some predatory fishes that inhabit pelagic environments, such as tunas, often school.
Sleep in fishes, all of which lack true eyelids, consists of a seemingly listless state in which the fish maintains its balance but moves slowly. If attacked or disturbed, most can dart away. A few kinds of fishes lie on the bottom to sleep. Most catfishes, some loaches, and some eels and electric fishes are strictly nocturnal, being active and hunting for food during the night and retiring during the day to holes, thick vegetation, or other protective parts of the environment.
Communication between members of a species or between members of two or more species often is extremely important, especially in breeding behaviour (see below Reproduction). The mode of communication may be visual, as between the small so-called cleaner fish and a large fish of a very different species. The larger fish often allows the cleaner to enter its mouth to remove gill parasites. The cleaner is recognized by its distinctive colour and actions and therefore is not eaten, even if the larger fish is normally a predator. Communication is often chemical, signals being sent by specific chemicals called pheromones.
Many fishes have a streamlined body and swim freely in open water. Fish locomotion is closely correlated with habitat and ecological niche (the general position of the animal to its environment).
Many fishes in both marine and fresh waters swim at the surface and have mouths adapted to feed best (and sometimes only) at the surface. Often such fishes are long and slender, able to dart at surface insects or at other surface fishes and in turn to dart away from predators; needlefishes, halfbeaks, and topminnows (such as killifish and mosquito fish) are good examples. Oceanic flying fishes escape their predators by gathering speed above the water surface, with the lower lobe of the tail providing thrust in the water. They then glide hundreds of yards on enlarged, winglike pectoral and pelvic fins. South American freshwater flying fishes escape their enemies by jumping and propelling their strongly keeled bodies out of the water.
So-called mid-water swimmers, the most common type of fish, are of many kinds and live in many habitats. The powerful fusiform tunas and the trouts, for example, are adapted for strong, fast swimming, the tunas to capture prey speedily in the open ocean and the trouts to cope with the swift currents of streams and rivers. The trout body form is well adapted to many habitats. Fishes that live in relatively quiet waters such as bays or lake shores or slow rivers usually are not strong, fast swimmers but are capable of short, quick bursts of speed to escape a predator. Many of these fishes have their sides flattened, examples being the sunfish and the freshwater angelfish of aquarists. Fish associated with the bottom or substrate usually are slow swimmers. Open-water plankton-feeding fishes almost always remain fusiform and are capable of rapid, strong movement (for example, sardines and herrings of the open ocean and also many small minnows of streams and lakes).
Bottom-living fishes are of many kinds and have undergone many types of modification of their body shape and swimming habits. Rays, which evolved from strong-swimming mid-water sharks, usually stay close to the bottom and move by undulating their large pectoral fins. Flounders live in a similar habitat and move over the bottom by undulating the entire body. Many bottom fishes dart from place to place, resting on the bottom between movements, a motion common in gobies. One goby relative, the mudskipper, has taken to living at the edge of pools along the shore of muddy mangrove swamps. It escapes its enemies by flipping rapidly over the mud, out of the water. Some catfishes, synbranchid eels, the so-called climbing perch, and a few other fishes venture out over damp ground to find more promising waters than those that they left. They move by wriggling their bodies, sometimes using strong pectoral fins; most have accessory air-breathing organs. Many bottom-dwelling fishes live in mud holes or rocky crevices. Marine eels and gobies commonly are found in such habitats and for the most part venture far beyond their cavelike homes. Some bottom dwellers, such as the clingfishes (Gobiesocidae), have developed powerful adhesive disks that enable them to remain in place on the substrate in areas such as rocky coasts, where the action of the waves is great.
The methods of reproduction in fishes are varied, but most fishes lay a large number of small eggs, fertilized and scattered outside of the body. The eggs of pelagic fishes usually remain suspended in the open water. Many shore and freshwater fishes lay eggs on the bottom or among plants. Some have adhesive eggs. The mortality of the young and especially of the eggs is very high, and often only a few individuals grow to maturity out of hundreds, thousands, and in some cases millions of eggs laid.
Males produce sperm, usually as a milky white substance called milt, in two (sometimes one) testes within the body cavity. In bony fishes a sperm duct leads from each testis to a urogenital opening behind the vent or anus. In sharks and rays and in cyclostomes the duct leads to a cloaca. Sometimes the pelvic fins are modified to help transmit the milt to the eggs at the female’s vent or on the substrate where the female has placed them. Sometimes accessory organs are used to fertilize females internally—for example, the claspers of many sharks and rays.
In the females the eggs are formed in two ovaries (sometimes only one) and pass through the ovaries to the urogenital opening and to the outside. In some fishes the eggs are fertilized internally but are shed before development takes place. Members of about a dozen families each of bony fishes (teleosts) and sharks bear live young. Many skates and rays also bear live young. In some bony fishes the eggs simply develop within the female, the young emerging when the eggs hatch (ovoviviparous). Others develop within the ovary and are nourished by ovarian tissues after hatching (viviparous). There are also other methods utilized by fishes to nourish young within the female. In all live-bearers the young are born at a relatively large size and are few in number. In one family of primarily marine fishes, the surfperches from the Pacific coast of North America, Japan, and Korea, the males of at least one species are born sexually mature, although they are not fully grown.
Some fishes are hermaphroditic—an individual producing both sperm and eggs, usually at different stages of its life. Self-fertilization, however, is probably rare.
Successful reproduction and, in many cases, defense of the eggs and the young are assured by rather stereotypical but often elaborate courtship and parental behaviour, either by the male or the female or both. Some fishes prepare nests by hollowing out depressions in the sand bottom (cichlids, for example), build nests with plant materials and sticky threads excreted by the kidneys (sticklebacks), or blow a cluster of mucus-covered bubbles at the water surface (gouramis). The eggs are laid in these structures. Some varieties of cichlids and catfishes incubate eggs in their mouths.
Some fishes, such as salmon, undergo long migrations from the ocean and up large rivers to spawn in the gravel beds where they themselves hatched (anadromous fishes). Some, such as the freshwater eels (family Anguillidae), live and grow to maturity in fresh water and migrate to the sea to spawn (catadromous fishes). Other fishes undertake shorter migrations from lakes into streams, within the ocean, or enter spawning habitats that they do not ordinarily occupy in other ways.
The basic structure and function of the fish body are similar to those of all other vertebrates. The usual four types of tissues are present: surface or epithelial, connective (bone, cartilage, and fibrous tissues, as well as their derivative, blood), nerve, and muscle tissues. In addition, the fish’s organs and organ systems parallel those of other vertebrates.
The typical fish body is streamlined and spindle-shaped, with an anterior head, a gill apparatus, and a heart, the latter lying in the midline just below the gill chamber. The body cavity, containing the vital organs, is situated behind the head in the lower anterior part of the body. The anus usually marks the posterior termination of the body cavity and most often occurs just in front of the base of the anal fin. The spinal cord and vertebral column continue from the posterior part of the head to the base of the tail fin, passing dorsal to the body cavity and through the caudal (tail) region behind the body cavity. Most of the body is of muscular tissue, a high proportion of which is necessitated by swimming. In the course of evolution this basic body plan has been modified repeatedly into the many varieties of fish shapes that exist today.
The skeleton forms an integral part of the fish’s locomotion system, as well as serving to protect vital parts. The internal skeleton consists of the skull bones (except for the roofing bones of the head, which are really part of the external skeleton), the vertebral column, and the fin supports (fin rays). The fin supports are derived from the external skeleton but will be treated here because of their close functional relationship to the internal skeleton. The internal skeleton of cyclostomes, sharks, and rays is of cartilage; that of many fossil groups and some primitive living fishes is mostly of cartilage but may include some bone. In place of the vertebral column, the earliest vertebrates had a fully developed notochord, a flexible stiff rod of viscous cells surrounded by a strong fibrous sheath. During the evolution of modern fishes the rod was replaced in part by cartilage and then by ossified cartilage. Sharks and rays retain a cartilaginous vertebral column; bony fishes have spool-shaped vertebrae that in the more primitive living forms only partially replace the notochord. The skull, including the gill arches and jaws of bony fishes, is fully, or at least partially, ossified. That of sharks and rays remains cartilaginous, at times partially replaced by calcium deposits but never by true bone.
The supportive elements of the fins (basal or radial bones or both) have changed greatly during fish evolution. Some of these changes are described in the section below (Evolution and paleontology). Most fishes possess a single dorsal fin on the midline of the back. Many have two and a few have three dorsal fins. The other fins are the single tail and anal fins and paired pelvic and pectoral fins. A small fin, the adipose fin, with hairlike fin rays, occurs in many of the relatively primitive teleosts (such as trout) on the back near the base of the caudal fin.
The skin of a fish must serve many functions. It aids in maintaining the osmotic balance, provides physical protection for the body, is the site of coloration, contains sensory receptors, and, in some fishes, functions in respiration. Mucous glands, which aid in maintaining the water balance and offer protection from bacteria, are extremely numerous in fish skin, especially in cyclostomes and teleosts. Since mucous glands are present in the modern lampreys, it is reasonable to assume that they were present in primitive fishes, such as the ancient Silurian and Devonian agnathans. Protection from abrasion and predation is another function of the fish skin, and dermal (skin) bone arose early in fish evolution in response to this need. It is thought that bone first evolved in skin and only later invaded the cartilaginous areas of the fish’s body, to provide additional support and protection. There is some argument as to which came first, cartilage or bone, and fossil evidence does not settle the question. In any event, dermal bone has played an important part in fish evolution and has different characteristics in different groups of fishes. Several groups are characterized at least in part by the kind of bony scales they possess.
Scales have played an important part in the evolution of fishes. Primitive fishes usually had thick bony plates or thick scales in several layers of bone, enamel, and related substances. Modern teleost fishes have scales of bone, which, while still protective, allow much more freedom of motion in the body. A few modern teleosts (some catfishes, sticklebacks, and others) have secondarily acquired bony plates in the skin. Modern and early sharks possessed placoid scales, a relatively primitive type of scale with a toothlike structure, consisting of an outside layer of enamel-like substance (vitrodentine), an inner layer of dentine, and a pulp cavity containing nerves and blood vessels. Primitive bony fishes had thick scales of either the ganoid or the cosmoid type. Cosmoid scales have a hard, enamel-like outer layer, an inner layer of cosmine (a form of dentine), and then a layer of vascular bone (isopedine). In ganoid scales the hard outer layer is different chemically and is called ganoin. Under this is a cosminelike layer and then a vascular bony layer. The thin, translucent bony scales of modern fishes, called cycloid and ctenoid (the latter distinguished by serrations at the edges), lack enameloid and dentine layers.
Skin has several other functions in fishes. It is well supplied with nerve endings and presumably receives tactile, thermal, and pain stimuli. Skin is also well supplied with blood vessels. Some fishes breathe in part through the skin, by the exchange of oxygen and carbon dioxide between the surrounding water and numerous small blood vessels near the skin surface.
Skin serves as protection through the control of coloration. Fishes exhibit an almost limitless range of colours. The colours often blend closely with the surroundings, effectively hiding the animal. Many fishes use bright colours for territorial advertisement or as recognition marks for other members of their own species, or sometimes for members of other species. Many fishes can change their colour to a greater or lesser degree, by movement of pigment within the pigment cells (chromatophores). Black pigment cells (melanophores), of almost universal occurrence in fishes, are often juxtaposed with other pigment cells. When placed beneath iridocytes or leucophores (bearing the silvery or white pigment guanine), melanophores produce structural colours of blue and green. These colours are often extremely intense, because they are formed by refraction of light through the needlelike crystals of guanine. The blue and green refracted colours are often relatively pure, lacking the red and yellow rays, which have been absorbed by the black pigment (melanin) of the melanophores. Yellow, orange, and red colours are produced by erythrophores, cells containing the appropriate carotenoid pigments. Other colours are produced by combinations of melanophores, erythrophores, and iridocytes.
The major portion of the body of most fishes consists of muscles. Most of the mass is trunk musculature, the fin muscles usually being relatively small. The caudal fin is usually the most powerful fin, being moved by the trunk musculature. The body musculature is usually arranged in rows of chevron-shaped segments on each side. Contractions of these segments, each attached to adjacent vertebrae and vertebral processes, bends the body on the vertebral joint, producing successive undulations of the body, passing from the head to the tail, and producing driving strokes of the tail. It is the latter that provides the strong forward movement for most fishes.
The digestive system, in a functional sense, starts at the mouth, with the teeth used to capture prey or collect plant foods. Mouth shape and tooth structure vary greatly in fishes, depending on the kind of food normally eaten. Most fishes are predacious, feeding on small invertebrates or other fishes and have simple conical teeth on the jaws, on at least some of the bones of the roof of the mouth, and on special gill arch structures just in front of the esophagus. The latter are throat teeth. Most predacious fishes swallow their prey whole, and the teeth are used for grasping and holding prey, for orienting prey to be swallowed (head first) and for working the prey toward the esophagus. There are a variety of tooth types in fishes. Some fishes, such as sharks and piranhas, have cutting teeth for biting chunks out of their victims. A shark’s tooth, although superficially like that of a piranha, appears in many respects to be a modified scale, while that of the piranha is like that of other bony fishes, consisting of dentine and enamel. Parrot fishes have beaklike mouths with short incisor-like teeth for breaking off coral and have heavy pavementlike throat teeth for crushing the coral. Some catfishes have small brushlike teeth, arranged in rows on the jaws, for scraping plant and animal growth from rocks. Many fishes (such as the Cyprinidae or minnows) have no jaw teeth at all but have very strong throat teeth.
Some fishes gather planktonic food by straining it from their gill cavities with numerous elongate stiff rods (gill rakers) anchored by one end to the gill bars. The food collected on these rods is passed to the throat, where it is swallowed. Most fishes have only short gill rakers that help keep food particles from escaping out the mouth cavity into the gill chamber.
Once reaching the throat, food enters a short, often greatly distensible esophagus, a simple tube with a muscular wall leading into a stomach. The stomach varies greatly in fishes, depending upon the diet. In most predacious fishes it is a simple straight or curved tube or pouch with a muscular wall and a glandular lining. Food is largely digested there and leaves the stomach in liquid form.
Between the stomach and the intestine, ducts enter the digestive tube from the liver and pancreas. The liver is a large, clearly defined organ. The pancreas may be embedded in it, diffused through it, or broken into small parts spread along some of the intestine. The junction between the stomach and the intestine is marked by a muscular valve. Pyloric ceca (blind sacs) occur in some fishes at this junction and have a digestive or absorptive function or both.
The intestine itself is quite variable in length, depending upon the fish’s diet. It is short in predacious forms, sometimes no longer than the body cavity, but long in herbivorous forms, being coiled and several times longer than the entire length of the fish in some species of South American catfishes. The intestine is primarily an organ for absorbing nutrients into the bloodstream. The larger its internal surface, the greater its absorptive efficiency, and a spiral valve is one method of increasing its absorption surface.
Sharks, rays, chimaeras, lungfishes, surviving chondrosteans, holosteans, and even a few of the more primitive teleosts have a spiral valve or at least traces of it in the intestine. Most modern teleosts have increased the area of the intestinal walls by having numerous folds and villi (fingerlike projections) somewhat like those in humans. Undigested substances are passed to the exterior through the anus in most teleost fishes. In lungfishes, sharks, and rays, it is first passed through the cloaca, a common cavity receiving the intestinal opening and the ducts from the urogenital system.
Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills. The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour. Water taken in continuously through the mouth passes backward between the gill bars and over the gill filaments, where the exchange of gases takes place. The gills are protected by a gill cover in teleosts and many other fishes but by flaps of skin in sharks, rays, and some of the older fossil fish groups. The blood capillaries in the gill filaments are close to the gill surface to take up oxygen from the water and to give up excess carbon dioxide to the water.
Most modern fishes have a hydrostatic (ballast) organ, called the swim bladder, that lies in the body cavity just below the kidney and above the stomach and intestine. It originated as a diverticulum of the digestive canal. In advanced teleosts, especially the acanthopterygians, the bladder has lost its connection with the digestive tract, a condition called physoclistic. The connection has been retained (physostomous) by many relatively primitive teleosts. In several unrelated lines of fishes, the bladder has become specialized as a lung or, at least, as a highly vascularized accessory breathing organ. Some fishes with such accessory organs are obligate air breathers and will drown if denied access to the surface, even in well-oxygenated water. Fishes with a hydrostatic form of swim bladder can control their depth by regulating the amount of gas in the bladder. The gas, mostly oxygen, is secreted into the bladder by special glands, rendering the fish more buoyant; the gas is absorbed into the bloodstream by another special organ, reducing the overall buoyancy and allowing the fish to sink. Some deep-sea fishes may have oils, rather than gas, in the bladder. Other deep-sea and some bottom-living forms have much-reduced swim bladders or have lost the organ entirely.
The swim bladder of fishes follows the same developmental pattern as the lungs of land vertebrates. There is no doubt that the two structures have the same historical origin in primitive fishes. More or less intermediate forms still survive among the more primitive types of fishes, such as the lungfishes Lepidosiren and Protopterus.
The circulatory, or blood vascular, system consists of the heart, the arteries, the capillaries, and the veins. It is in the capillaries that the interchange of oxygen, carbon dioxide, nutrients, and other substances such as hormones and waste products takes place. The capillaries lead to the veins, which return the venous blood with its waste products to the heart, kidneys, and gills. There are two kinds of capillary beds: those in the gills and those in the rest of the body. The heart, a folded continuous muscular tube with three or four saclike enlargements, undergoes rhythmic contractions and receives venous blood in a sinus venosus. It passes the blood to an auricle and then into a thick muscular pump, the ventricle. From the ventricle the blood goes to a bulbous structure at the base of a ventral aorta just below the gills. The blood passes to the afferent (receiving) arteries of the gill arches and then to the gill capillaries. There waste gases are given off to the environment, and oxygen is absorbed. The oxygenated blood enters efferent (exuant) arteries of the gill arches and then flows into the dorsal aorta. From there blood is distributed to the tissues and organs of the body. One-way valves prevent backflow. The circulation of fishes thus differs from that of the reptiles, birds, and mammals in that oxygenated blood is not returned to the heart prior to distribution to the other parts of the body.
The primary excretory organ in fishes, as in other vertebrates, is the kidney. In fishes some excretion also takes place in the digestive tract, skin, and especially the gills (where ammonia is given off). Compared with land vertebrates, fishes have a special problem in maintaining their internal environment at a constant concentration of water and dissolved substances, such as salts. Proper balance of the internal environment (homeostasis) of a fish is in a great part maintained by the excretory system, especially the kidney.
The kidney, gills, and skin play an important role in maintaining a fish’s internal environment and checking the effects of osmosis. Marine fishes live in an environment in which the water around them has a greater concentration of salts than they can have inside their body and still maintain life. Freshwater fishes, on the other hand, live in water with a much lower concentration of salts than they require inside their bodies. Osmosis tends to promote the loss of water from the body of a marine fish and absorption of water by that of a freshwater fish. Mucus in the skin tends to slow the process but is not a sufficient barrier to prevent the movement of fluids through the permeable skin. When solutions on two sides of a permeable membrane have different concentrations of dissolved substances, water will pass through the membrane into the more concentrated solution, while the dissolved chemicals move into the area of lower concentration (diffusion).
The kidney of freshwater fishes is often larger in relation to body weight than that of marine fishes. In both groups the kidney excretes wastes from the body, but the kidney of freshwater fishes also excretes large amounts of water, counteracting the water absorbed through the skin. Freshwater fishes tend to lose salt to the environment and must replace it. They get some salt from their food, but the gills and skin inside the mouth actively absorb salt from water passed through the mouth. This absorption is performed by special cells capable of moving salts against the diffusion gradient. Freshwater fishes drink very little water and take in little water with their food.
Marine fishes must conserve water, and therefore their kidneys excrete little water. To maintain their water balance, marine fishes drink large quantities of seawater, retaining most of the water and excreting the salt. Most nitrogenous waste in marine fishes appears to be secreted by the gills as ammonia. Marine fishes can excrete salt by clusters of special cells (chloride cells) in the gills.
There are several teleosts—for example, the salmon—that travel between fresh water and seawater and must adjust to the reversal of osmotic gradients. They adjust their physiological processes by spending time (often surprisingly little time) in the intermediate brackish environment.
Marine hagfishes, sharks, and rays have osmotic concentrations in their blood about equal to that of seawater and so do not have to drink water nor perform much physiological work to maintain their osmotic balance. In sharks and rays the osmotic concentration is kept high by retention of urea in the blood. Freshwater sharks have a lowered concentration of urea in the blood.
Endocrine glands secrete their products into the bloodstream and body tissues and, along with the central nervous system, control and regulate many kinds of body functions. Cyclostomes have a well-developed endocrine system, and presumably it was well developed in the early Agnatha, ancestral to modern fishes. Although the endocrine system in fishes is similar to that of higher vertebrates, there are numerous differences in detail. The pituitary, the thyroid, the suprarenals, the adrenals, the pancreatic islets, the sex glands (ovaries and testes), the inner wall of the intestine, and the bodies of the ultimobranchial gland make up the endocrine system in fishes. There are some others whose function is not well understood. These organs regulate sexual activity and reproduction, growth, osmotic pressure, general metabolic activities such as the storage of fat and the utilization of foodstuffs, blood pressure, and certain aspects of skin colour. Many of these activities are also controlled in part by the central nervous system, which works with the endocrine system in maintaining the life of a fish. Some parts of the endocrine system are developmentally, and undoubtedly evolutionarily, derived from the nervous system.
As in all vertebrates, the nervous system of fishes is the primary mechanism coordinating body activities, as well as integrating these activities in the appropriate manner with stimuli from the environment. The central nervous system, consisting of the brain and spinal cord, is the primary integrating mechanism. The peripheral nervous system, consisting of nerves that connect the brain and spinal cord to various body organs, carries sensory information from special receptor organs such as the eyes, internal ears, nares (sense of smell), taste glands, and others to the integrating centres of the brain and spinal cord. The peripheral nervous system also carries information via different nerve cells from the integrating centres of the brain and spinal cord. This coded information is carried to the various organs and body systems, such as the skeletal muscular system, for appropriate action in response to the original external or internal stimulus. Another branch of the nervous system, the autonomic nervous system, helps to coordinate the activities of many glands and organs and is itself closely connected to the integrating centres of the brain.
The brain of the fish is divided into several anatomical and functional parts, all closely interconnected but each serving as the primary centre of integrating particular kinds of responses and activities. Several of these centres or parts are primarily associated with one type of sensory perception, such as sight, hearing, or smell (olfaction).
The sense of smell is important in almost all fishes. Certain eels with tiny eyes depend mostly on smell for location of food. The olfactory, or nasal, organ of fishes is located on the dorsal surface of the snout. The lining of the nasal organ has special sensory cells that perceive chemicals dissolved in the water, such as substances from food material, and send sensory information to the brain by way of the first cranial nerve. Odour also serves as an alarm system. Many fishes, especially various species of freshwater minnows, react with alarm to a chemical released from the skin of an injured member of their own species.
Many fishes have a well-developed sense of taste, and tiny pitlike taste buds or organs are located not only within their mouth cavities but also over their heads and parts of their body. Catfishes, which often have poor vision, have barbels (“whiskers”) that serve as supplementary taste organs, those around the mouth being actively used to search out food on the bottom. Some species of naturally blind cave fishes are especially well supplied with taste buds, which often cover most of their body surface.
Sight is extremely important in most fishes. The eye of a fish is basically like that of all other vertebrates, but the eyes of fishes are extremely varied in structure and adaptation. In general, fishes living in dark and dim water habitats have large eyes, unless they have specialized in some compensatory way so that another sense (such as smell) is dominant, in which case the eyes will often be reduced. Fishes living in brightly lighted shallow waters often will have relatively small but efficient eyes. Cyclostomes have somewhat less elaborate eyes than other fishes, with skin stretched over the eyeball perhaps making their vision somewhat less effective. Most fishes have a spherical lens and accommodate their vision to far or near subjects by moving the lens within the eyeball. A few sharks accommodate by changing the shape of the lens, as in land vertebrates. Those fishes that are heavily dependent upon the eyes have especially strong muscles for accommodation. Most fishes see well, despite the restrictions imposed by frequent turbidity of the water and by light refraction.
Fossil evidence suggests that colour vision evolved in fishes more than 300 million years ago, but not all living fishes have retained this ability. Experimental evidence indicates that many shallow-water fishes, if not all, have colour vision and see some colours especially well, but some bottom-dwelling shore fishes live in areas where the water is sufficiently deep to filter out most if not all colours, and these fishes apparently never see colours. When tested in shallow water, they apparently are unable to respond to colour differences.
Sound perception and balance are intimately associated senses in a fish. The organs of hearing are entirely internal, located within the skull, on each side of the brain and somewhat behind the eyes. Sound waves, especially those of low frequencies, travel readily through water and impinge directly upon the bones and fluids of the head and body, to be transmitted to the hearing organs. Fishes readily respond to sound; for example, a trout conditioned to escape by the approach of fishermen will take flight upon perceiving footsteps on a stream bank even if it cannot see a fisherman. Compared with humans, however, the range of sound frequencies heard by fishes is greatly restricted. Many fishes communicate with each other by producing sounds in their swim bladders, in their throats by rasping their teeth, and in other ways.
A fish or other vertebrate seldom has to rely on a single type of sensory information to determine the nature of the environment around it. A catfish uses taste and touch when examining a food object with its oral barbels. Like most other animals, fishes have many touch receptors over their body surface. Pain and temperature receptors also are present in fishes and presumably produce the same kind of information to a fish as to humans. Fishes react in a negative fashion to stimuli that would be painful to human beings, suggesting that they feel a sensation of pain.
An important sensory system in fishes that is absent in other vertebrates (except some amphibians) is the lateral line system. This consists of a series of heavily innervated small canals located in the skin and bone around the eyes, along the lower jaw, over the head, and down the mid-side of the body, where it is associated with the scales. Intermittently along these canals are located tiny sensory organs (pit organs) that apparently detect changes in pressure. The system allows a fish to sense changes in water currents and pressure, thereby helping the fish to orient itself to the various changes that occur in the physical environment.
Woodpeckers (Picidae) are a diverse family of birds known for their unique adaptations and behaviors. With over 200 species distributed worldwide, woodpeckers have a rich evolutionary history that spans millions of years. In this brief overview, we will explore the key aspects of woodpecker evolution and their fascinating journey through time.
Woodpeckers belong to the order Piciformes, which also includes toucans, barbets, and honeyguides. Their evolutionary origins can be traced back to the early Eocene period, approximately 55 million years ago. Fossil records indicate that the earliest woodpeckers shared similarities with modern forms, possessing a sturdy beak and zygodactyl feet (two toes pointing forward and two backward) that allowed them to cling to trees and excavate cavities.
The ancestral woodpeckers likely inhabited forests and woodlands, where they foraged for insects, larvae, and other invertebrates found beneath the bark or within dead wood. Their specialized beak, reinforced with hard keratin and a chisel-like tip, enabled them to drill into tree trunks and extract prey. This feeding strategy provided a selective advantage, driving the diversification and adaptive radiation of woodpeckers into various ecological niches.
Over time, woodpeckers underwent further evolutionary adaptations. One of their most remarkable features is the presence of a hyoid apparatus, a complex arrangement of bones and muscles that supports the tongue. The long, extensible tongue can be extended well beyond the bill, allowing woodpeckers to reach deep into crevices and extract hidden prey. This tongue mechanism is unique among birds and contributes to their success as specialized insectivores.
Another notable adaptation is the protective features that enable woodpeckers to withstand the repetitive impacts of drumming and excavating. Their brain is encased in a thick, sponge-like skull that acts as a shock absorber, reducing the risk of brain injury. Furthermore, their strong neck muscles and specialized arrangement of bones and cartilage in the skull help distribute the forces generated during pecking, minimizing the strain on their brain and neck.
Woodpecker evolution has also led to remarkable diversity in terms of size, coloration, and behavior. Some species, like the great spotted woodpecker (Dendrocopos major), exhibit striking black-and-white plumage with red patches, while others, such as the pileated woodpecker (Dryocopus pileatus), have predominantly black feathers with a vibrant crest. These variations serve various functions, including communication, mate attraction, and camouflage.
Woodpeckers are known for their distinct drumming and vocalizations, which play a crucial role in communication and territorial defense. Drumming, achieved by rapid pecking on resonant surfaces like dead wood or metal, serves to establish their presence and ward off potential rivals. Additionally, woodpeckers produce a variety of calls, ranging from rhythmic drum rolls to chirps and rattles, allowing them to communicate with conspecifics across their habitat.
The evolutionary success of woodpeckers is evident in their global distribution, with species inhabiting diverse habitats such as forests, woodlands, savannas, and even deserts. They have adapted to various environmental conditions, exploiting niches that offer abundant food resources and suitable nesting sites.
In summary, woodpeckers have a long and fascinating evolutionary history that has shaped their unique adaptations and behaviors. From their early origins as insectivorous tree-dwellers to their diverse forms found across the globe today, woodpeckers are a testament to the incredible adaptability and resilience of life. Studying these remarkable birds provides valuable insights into the intricate relationship between form, function, and the ecological roles they play in their respective habitats.
Mother and bay otter bonding, Morro Bay California. he sea otter (Enhydra lutris) is a marine mammal native to the coasts of the northern and eastern North Pacific Ocean. Adult sea otters typically weigh between 14 and 45 kg (30 and 100 lb), making them the heaviest members of the weasel family, but among[3] the smallest marine mammals. Unlike most marine mammals, the sea otter's primary form of insulation is an exceptionally thick coat of fur, the densest in the animal kingdom. Although it can walk on land, the sea otter is capable of living exclusively in the ocean.
The sea otter inhabits nearshore environments, where it dives to the sea floor to forage. It preys mostly on marine invertebrates such as sea urchins, various mollusks and crustaceans, and some species of fish. Its foraging and eating habits are noteworthy in several respects. Its use of rocks to dislodge prey and to open shells makes it one of the few mammal species to use tools. In most of its range, it is a keystone species, controlling sea urchin populations which would otherwise inflict extensive damage to kelp forest ecosystems.[4] Its diet includes prey species that are also valued by humans as food, leading to conflicts between sea otters and fisheries.
Sea otters, whose numbers were once estimated at 150,000–300,000, were hunted extensively for their fur between 1741 and 1911, and the world population fell to 1,000–2,000 individuals living in a fraction of their historic range.[5] A subsequent international ban on hunting, sea otter conservation efforts, and reintroduction programs into previously populated areas have contributed to numbers rebounding, and the species occupies about two-thirds of its former range. The recovery of the sea otter is considered an important success in marine conservation, although populations in the Aleutian Islands and California have recently declined or have plateaued at depressed levels. For these reasons, the sea otter remains classified as an endangered species.
Evolution
The sea otter is the heaviest (the giant otter is longer, but significantly slimmer) member of the family Mustelidae,[6] a diverse group that includes the 13 otter species and terrestrial animals such as weasels, badgers, and minks. It is unique among the mustelids in not making dens or burrows, in having no functional anal scent glands,[7] and in being able to live its entire life without leaving the water.[8] The only living member of the genus Enhydra, the sea otter is so different from other mustelid species that, as recently as 1982, some scientists believed it was more closely related to the earless seals.[9] Genetic analysis indicates the sea otter and its closest extant relatives, which include the African speckle-throated otter, Eurasian otter, African clawless otter and Asian small-clawed otter, shared an ancestor approximately 5 million years ago.[10]
Fossil evidence indicates the Enhydra lineage became isolated in the North Pacific approximately 2 million years ago, giving rise to the now-extinct Enhydra macrodonta and the modern sea otter, Enhydra lutris.[11] One related species has been described, Enhydra reevei, from the Pleistocene of East Anglia.[12] The modern sea otter evolved initially in northern Hokkaidō and Russia, and then spread east to the Aleutian Islands, mainland Alaska, and down the North American coast.[13] In comparison to cetaceans, sirenians, and pinnipeds, which entered the water approximately 50, 40, and 20 million years ago, respectively, the sea otter is a relative newcomer to a marine existence.[14] In some respects, though, the sea otter is more fully adapted to water than pinnipeds, which must haul out on land or ice to give birth.[15] The full genome of the northern sea otter (Enhydra lutris kenyoni) was sequenced in 2017 and may allow for examination of the sea otter's evolutionary divergence from terrestrial mustelids.[16]
Taxonomy
Lutrinae
Pteronura (giant otter)
Lontra (4 species)
Enhydra (sea otter)
Hydrictis
(spotted-necked otter)
Lutra (2 species)
Aonyx
(African clawless)
Amblonyx
(Asian small-clawed)
Lutrogale
(smooth-coated)
Cladogram showing relationships between sea otters and other otters[17][18]
The first scientific description of the sea otter is contained in the field notes of Georg Steller from 1751, and the species was described by Carl Linnaeus in his landmark 1758 10th edition of Systema Naturae.[19] Originally named Lutra marina, it underwent numerous name changes before being accepted as Enhydra lutris in 1922.[11] The generic name Enhydra, derives from the Ancient Greek en/εν "in" and hydra/ύδρα "water",[20] meaning "in the water", and the Latin word lutris, meaning "otter".[21] It was formerly sometimes referred to as the "sea beaver".[22]
Subspecies
Three subspecies of the sea otter are recognized with distinct geographical distributions. Enhydra lutris lutris (nominate), the Asian sea otter, ranges across Russia's Kuril Islands northeast of Japan, and the Commander Islands in the northwestern Pacific Ocean. In the eastern Pacific Ocean, E. l. kenyoni, the northern sea otter, is found from Alaska's Aleutian Islands to Oregon and E. l. nereis, the southern sea otter, is native to central and southern California.[23] The Asian sea otter is the largest subspecies and has a slightly wider skull and shorter nasal bones than both other subspecies. Northern sea otters possess longer mandibles (lower jaws) while southern sea otters have longer rostrums and smaller teeth.[24][25]
Description
A sea otter's thick fur makes its body appear plumper on land than in the water.
Skull of a sea otter
The sea otter is one of the smallest marine mammal species, but it is the heaviest mustelid.[8] Male sea otters usually weigh 22 to 45 kg (49 to 99 lb) and are 1.2 to 1.5 m (3 ft 11 in to 4 ft 11 in) in length, though specimens up to 54 kg (119 lb) have been recorded.[26] Females are smaller, weighing 14 to 33 kg (31 to 73 lb) and measuring 1.0 to 1.4 m (3 ft 3 in to 4 ft 7 in) in length.[27] For its size, the male otter's baculum is very large, massive and bent upwards, measuring 150 mm (5+7⁄8 in) in length and 15 mm (9⁄16 in) at the base.[28]
Unlike most other marine mammals, the sea otter has no blubber and relies on its exceptionally thick fur to keep warm.[29] With up to 150,000 strands of hair per square centimetre (970,000/in2), its fur is the densest of any animal.[30] The fur consists of long, waterproof guard hairs and short underfur; the guard hairs keep the dense underfur layer dry.[27] There is an air compartment between the thick fur and the skin where air is trapped and heated by the body.[31] Cold water is kept completely away from the skin and heat loss is limited.[27] However, a potential disadvantage of this form of insulation is compression of the air layer as the otter dives, thereby reducing the insulating quality of fur at depth when the animal forages.[31] The fur is thick year-round, as it is shed and replaced gradually rather than in a distinct molting season.[32] As the ability of the guard hairs to repel water depends on utmost cleanliness, the sea otter has the ability to reach and groom the fur on any part of its body, taking advantage of its loose skin and an unusually supple skeleton.[33] The coloration of the pelage is usually deep brown with silver-gray speckles, but it can range from yellowish or grayish brown to almost black.[34] In adults, the head, throat, and chest are lighter in color than the rest of the body.[34]
The sea otter displays numerous adaptations to its marine environment. The nostrils and small ears can close.[35] The hind feet, which provide most of its propulsion in swimming, are long, broadly flattened, and fully webbed.[36] The fifth digit on each hind foot is longest, facilitating swimming while on its back, but making walking difficult.[37] The tail is fairly short, thick, slightly flattened, and muscular. The front paws are short with retractable claws, with tough pads on the palms that enable gripping slippery prey.[38] The bones show osteosclerosis, increasing their density to reduce buoyancy.[39]
The sea otter presents an insight into the evolutionary process of the mammalian invasion of the aquatic environment, which has occurred numerous times over the course of mammalian evolution.[40] Having only returned to the sea about 3 million years ago,[41] sea otters represent a snapshot at the earliest point of the transition from fur to blubber. In sea otters, fur is still advantageous, given their small nature and division of lifetime between the aquatic and terrestrial environments.[42] However, as sea otters evolve and adapt to spending more and more of their lifetimes in the sea, the convergent evolution of blubber suggests that the reliance on fur for insulation would be replaced by a dependency on blubber. This is particularly true due to the diving nature of the sea otter; as dives become lengthier and deeper, the air layer's ability to retain heat or buoyancy decreases,[31] while blubber remains efficient at both of those functions.[42] Blubber can also additionally serve as an energy source for deep dives,[43] which would most likely prove advantageous over fur in the evolutionary future of sea otters.
The sea otter propels itself underwater by moving the rear end of its body, including its tail and hind feet, up and down,[36] and is capable of speeds of up to 9 kilometres per hour (5.6 mph).[6] When underwater, its body is long and streamlined, with the short forelimbs pressed closely against the chest.[44] When at the surface, it usually floats on its back and moves by sculling its feet and tail from side to side.[45] At rest, all four limbs can be folded onto the torso to conserve heat, whereas on particularly hot days, the hind feet may be held underwater for cooling.[46] The sea otter's body is highly buoyant because of its large lung capacity – about 2.5 times greater than that of similar-sized land mammals[47] – and the air trapped in its fur. The sea otter walks with a clumsy, rolling gait on land, and can run in a bounding motion.[37]
Long, highly sensitive whiskers and front paws help the sea otter find prey by touch when waters are dark or murky.[48] Researchers have noted when they approach in plain view, sea otters react more rapidly when the wind is blowing towards the animals, indicating the sense of smell is more important than sight as a warning sense.[49] Other observations indicate the sea otter's sense of sight is useful above and below the water, although not as good as that of seals.[50] Its hearing is neither particularly acute nor poor.[51]
An adult's 32 teeth, particularly the molars, are flattened and rounded for crushing rather than cutting food.[52] Seals and sea otters are the only carnivores with two pairs of lower incisor teeth rather than three;[53] the adult dental formula is
3.1.3.1
2.1.3.2
.[54] The teeth and bones are sometimes stained purple as a result of ingesting sea urchins.[55] The sea otter has a metabolic rate two or three times that of comparatively sized terrestrial mammals. It must eat an estimated 25 to 38% of its own body weight in food each day to burn the calories necessary to counteract the loss of heat due to the cold water environment.[56][57] Its digestive efficiency is estimated at 80 to 85%,[58] and food is digested and passed in as little as three hours.[29] Most of its need for water is met through food, although, in contrast to most other marine mammals, it also drinks seawater. Its relatively large kidneys enable it to derive fresh water from sea water and excrete concentrated urine.[59]
Behavior
Sensitive vibrissae and forepaws enable sea otters to find prey (like this purple sea urchin) using their sense of touch.
The sea otter is diurnal. It has a period of foraging and eating in the morning, starting about an hour before sunrise, then rests or sleeps in mid-day.[60] Foraging resumes for a few hours in the afternoon and subsides before sunset, and a third foraging period may occur around midnight.[60] Females with pups appear to be more inclined to feed at night.[60] Observations of the amount of time a sea otter must spend each day foraging range from 24 to 60%, apparently depending on the availability of food in the area.[61]
Sea otters spend much of their time grooming, which consists of cleaning the fur, untangling knots, removing loose fur, rubbing the fur to squeeze out water and introduce air, and blowing air into the fur. To casual observers, it appears as if the animals are scratching, but they are not known to have lice or other parasites in the fur.[62] When eating, sea otters roll in the water frequently, apparently to wash food scraps from their fur.[63]
A sea otter grooming itself by rubbing its dense coat.
Foraging
See also: Physiology of underwater diving
The sea otter hunts in short dives, often to the sea floor. Although it can hold its breath for up to five minutes,[35] its dives typically last about one minute and not more than four.[27] It is the only marine animal capable of lifting and turning over rocks, which it often does with its front paws when searching for prey.[63] The sea otter may also pluck snails and other organisms from kelp and dig deep into underwater mud for clams.[63] It is the only marine mammal that catches fish with its forepaws rather than with its teeth.[29]
A sea otter in captivity in Japan, 2015
Under each foreleg, the sea otter has a loose pouch of skin that extends across the chest. In this pouch (preferentially the left one), the animal stores collected food to bring to the surface. This pouch also holds a rock, unique to the otter, that is used to break open shellfish and clams.[64] At the surface, the sea otter eats while floating on its back, using its forepaws to tear food apart and bring it to its mouth. It can chew and swallow small mussels with their shells, whereas large mussel shells may be twisted apart.[65] It uses its lower incisor teeth to access the meat in shellfish.[66] To eat large sea urchins, which are mostly covered with spines, the sea otter bites through the underside where the spines are shortest, and licks the soft contents out of the urchin's shell.[65]
The sea otter's use of rocks when hunting and feeding makes it one of the few mammal species to use tools.[67] To open hard shells, it may pound its prey with both paws against a rock on its chest. To pry an abalone off its rock, it hammers the abalone shell using a large stone, with observed rates of 45 blows in 15 seconds.[27] Releasing an abalone, which can cling to rock with a force equal to 4,000 times its own body weight, requires multiple dives.[27]
Social structure
Sleeping sea otters holding paws at the Vancouver Aquarium[68] are kept afloat by their naturally high buoyancy.
Southern sea otters playing with one another at the Elkhorn Slough National Estuarine Research Reserve.
Although each adult and independent juvenile forages alone, sea otters tend to rest together in single-sex groups called rafts. A raft typically contains 10 to 100 animals, with male rafts being larger than female ones.[69] The largest raft ever seen contained over 2000 sea otters. To keep from drifting out to sea when resting and eating, sea otters may wrap themselves in kelp.[70]
A male sea otter is most likely to mate if he maintains a breeding territory in an area that is also favored by females.[71] As autumn is the peak breeding season in most areas, males typically defend their territory only from spring to autumn.[71] During this time, males patrol the boundaries of their territories to exclude other males,[71] although actual fighting is rare.[69] Adult females move freely between male territories, where they outnumber adult males by an average of five to one.[71] Males that do not have territories tend to congregate in large, male-only groups,[71] and swim through female areas when searching for a mate.[72]
The species exhibits a variety of vocal behaviors. The cry of a pup is often compared to that of a gull.[73] Females coo when they are apparently content; males may grunt instead.[74] Distressed or frightened adults may whistle, hiss, or in extreme circumstances, scream.[73] Although sea otters can be playful and sociable, they are not considered to be truly social animals.[75] They spend much time alone, and each adult can meet its own hunting, grooming, and defense needs.[75]
Reproduction and life cycle
While mating the male bites the nose of the female, often bloodying and scarring it.
Sea otters are polygynous: males have multiple female partners, typically those that inhabit their territory. If no territory is established, they seek out females in estrus. When a male sea otter finds a receptive female, the two engage in playful and sometimes aggressive behavior. They bond for the duration of estrus, or 3 days. The male holds the female's head or nose with his jaws during copulation. Visible scars are often present on females from this behavior.[6][76]
Births occur year-round, with peaks between May and June in northern populations and between January and March in southern populations.[77] Gestation appears to vary from four to twelve months, as the species is capable of delayed implantation followed by four months of pregnancy.[77] In California, sea otters usually breed every year, about twice as often as those in Alaska.[78]
Birth usually takes place in the water and typically produces a single pup weighing 1.4 to 2.3 kilograms (3 lb 1 oz to 5 lb 1 oz).[79] Twins occur in 2% of births; however, usually only one pup survives.[6] At birth, the eyes are open, ten teeth are visible, and the pup has a thick coat of baby fur.[80] Mothers have been observed to lick and fluff a newborn for hours; after grooming, the pup's fur retains so much air, the pup floats like a cork and cannot dive.[81] The fluffy baby fur is replaced by adult fur after about 13 weeks.[19]
A mother floats with her pup on her chest. Georg Steller wrote, "They embrace their young with an affection that is scarcely credible."[82]
Nursing lasts six to eight months in Californian populations and four to twelve months in Alaska, with the mother beginning to offer bits of prey at one to two months.[83] The milk from a sea otter's two abdominal nipples is rich in fat and more similar to the milk of other marine mammals than to that of other mustelids.[84] A pup, with guidance from its mother, practices swimming and diving for several weeks before it is able to reach the sea floor. Initially, the objects it retrieves are of little food value, such as brightly colored starfish and pebbles.[64] Juveniles are typically independent at six to eight months, but a mother may be forced to abandon a pup if she cannot find enough food for it;[85] at the other extreme, a pup may be nursed until it is almost adult size.[79] Pup mortality is high, particularly during an individual's first winter – by one estimate, only 25% of pups survive their first year.[85] Pups born to experienced mothers have the highest survival rates.[86]
Females perform all tasks of feeding and raising offspring, and have occasionally been observed caring for orphaned pups.[87] Much has been written about the level of devotion of sea otter mothers for their pups – a mother gives her infant almost constant attention, cradling it on her chest away from the cold water and attentively grooming its fur.[88] When foraging, she leaves her pup floating on the water, sometimes wrapped in kelp to keep it from floating away;[89] if the pup is not sleeping, it cries loudly until she returns.[90] Mothers have been known to carry their pups for days after the pups' deaths.[82]
Females become sexually mature at around three or four years of age and males at around five; however, males often do not successfully breed until a few years later.[91] A captive male sired offspring at age 19.[79] In the wild, sea otters live to a maximum age of 23 years,[27] with lifespans ranging from 10 to 15 years for males and 15–20 years for females.[92] Several captive individuals have lived past 20 years, and a female at the Seattle Aquarium named Etika died at the age of 28 years.[93] Sea otters in the wild often develop worn teeth, which may account for their apparently shorter lifespans.[94]
Population and distribution
Sea otters live in coastal waters 15 to 23 metres (49 to 75 ft) deep,[95] and usually stay within a kilometre (2⁄3 mi) of the shore.[96] They are found most often in areas with protection from the most severe ocean winds, such as rocky coastlines, thick kelp forests, and barrier reefs.[97] Although they are most strongly associated with rocky substrates, sea otters can also live in areas where the sea floor consists primarily of mud, sand, or silt.[98] Their northern range is limited by ice, as sea otters can survive amidst drift ice but not land-fast ice.[99] Individuals generally occupy a home range a few kilometres long, and remain there year-round.[100]
The sea otter population is thought to have once been 150,000 to 300,000,[22] stretching in an arc across the North Pacific from northern Japan to the central Baja California Peninsula in Mexico. The fur trade that began in the 1740s reduced the sea otter's numbers to an estimated 1,000 to 2,000 members in 13 colonies. Hunting records researched by historian Adele Ogden place the westernmost limit of the hunting grounds off the northern Japanese island of Hokkaido and the easternmost limit off Punta Morro Hermosa about 21+1⁄2 miles (34.6 km) south of Punta Eugenia, Baja California's westernmost headland in Mexico.[101]
In about two-thirds of its former range, the species is at varying levels of recovery, with high population densities in some areas and threatened populations in others. Sea otters currently have stable populations in parts of the Russian east coast, Alaska, British Columbia, Washington, and California, with reports of recolonizations in Mexico and Japan.[102] Population estimates made between 2004 and 2007 give a worldwide total of approximately 107,000 sea otters.[19][103][104][105][106]
Japan
Adele Ogden wrote in The California Sea Otter Trade that western sea otter were hunted "from Yezo northeastward past the Kuril Group and Kamchatka to the Aleutian Chain".[101] "Yezo" refers to the island province of Hokkaido, in northern Japan, where the country’s only confirmed population of western sea otter resides.[1] Sightings have been documented in the waters of Cape Nosappu, Erimo, Hamanaka and Nemuro, among other locations in the region. [107]
Russia
Currently, the most stable and secure part of the western sea otter's range is along the Russian Far East coastline, in the northwestern Pacific waters off of the country (namely Kamchatka and Sakhalin Island), occasionally being seen in and around the Sea of Okhotsk.[108] Before the 19th century, around 20,000 to 25,000 sea otters lived near the Kuril Islands, with more near Kamchatka and the Commander Islands. After the years of the Great Hunt, the population in these areas, currently part of Russia, was only 750.[103] By 2004, sea otters had repopulated all of their former habitat in these areas, with an estimated total population of about 27,000. Of these, about 19,000 are at the Kurils, 2,000 to 3,500 at Kamchatka and another 5,000 to 5,500 at the Commander Islands.[103] Growth has slowed slightly, suggesting the numbers are reaching carrying capacity.[103]
British Columbia
Along the North American coast south of Alaska, the sea otter's range is discontinuous. A remnant population survived off Vancouver Island into the 20th century, but it died out despite the 1911 international protection treaty, with the last sea otter taken near Kyuquot in 1929. From 1969 to 1972, 89 sea otters were flown or shipped from Alaska to the west coast of Vancouver Island. This population increased to over 5,600 in 2013 with an estimated annual growth rate of 7.2%, and their range on the island's west coast extended north to Cape Scott and across the Queen Charlotte Strait to the Broughton Archipelago and south to Clayoquot Sound and Tofino.[109][110] In 1989, a separate colony was discovered in the central British Columbia coast. It is not known if this colony, which numbered about 300 animals in 2004, was founded by transplanted otters or was a remnant population that had gone undetected.[105] By 2013, this population exceeded 1,100 individuals, was increasing at an estimated 12.6% annual rate, and its range included Aristazabal Island, and Milbanke Sound south to Calvert Island.[109] In 2008, Canada determined the status of sea otters to be "special concern".[111][112]
United States
Alaska
Alaska is the central area of the sea otter's range. In 1973, the population in Alaska was estimated at between 100,000 and 125,000 animals.[113] By 2006, though, the Alaska population had fallen to an estimated 73,000 animals.[104] A massive decline in sea otter populations in the Aleutian Islands accounts for most of the change; the cause of this decline is not known, although orca predation is suspected.[114] The sea otter population in Prince William Sound was also hit hard by the Exxon Valdez oil spill, which killed thousands of sea otters in 1989.[63]
Washington
In 1969 and 1970, 59 sea otters were translocated from Amchitka Island to Washington, and released near La Push and Point Grenville. The translocated population is estimated to have declined to between 10 and 43 individuals before increasing, reaching 208 individuals in 1989. As of 2017, the population was estimated at over 2,000 individuals, and their range extends from Point Grenville in the south to Cape Flattery in the north and east to Pillar Point along the Strait of Juan de Fuca.[19]
In Washington, sea otters are found almost exclusively on the outer coasts. They can swim as close as six feet off shore along the Olympic coast. Reported sightings of sea otters in the San Juan Islands and Puget Sound almost always turn out to be North American river otters, which are commonly seen along the seashore. However, biologists have confirmed isolated sightings of sea otters in these areas since the mid-1990s.[19]
Oregon
The last native sea otter in Oregon was probably shot and killed in 1906. In 1970 and 1971, a total of 95 sea otters were transplanted from Amchitka Island, Alaska to the Southern Oregon coast. However, this translocation effort failed and otters soon again disappeared from the state.[115] In 2004, a male sea otter took up residence at Simpson Reef off of Cape Arago for six months. This male is thought to have originated from a colony in Washington, but disappeared after a coastal storm.[116] On 18 February 2009, a male sea otter was spotted in Depoe Bay off the Oregon Coast. It could have traveled to the state from either California or Washington.[117]
California
California's remote areas of coastline sheltered small colonies of sea otters through the fur trade. The 50 that survived in California, which were rediscovered in 1938, have since reproduced to almost 3,000.
The historic population of California sea otters was estimated at 16,000 before the fur trade decimated the population, leading to their assumed extinction. Today's population of California sea otters are the descendants of a single colony of about 50 sea otters located near Bixby Creek Bridge in March 1938 by Howard G. Sharpe, owner of the nearby Rainbow Lodge on Bixby Bridge in Big Sur.[118][119][120] Their principal range has gradually expanded and extends from Pigeon Point in San Mateo County to Santa Barbara County.[121]
Sea otters were once numerous in San Francisco Bay.[122][123] Historical records revealed the Russian-American Company snuck Aleuts into San Francisco Bay multiple times, despite the Spanish capturing or shooting them while hunting sea otters in the estuaries of San Jose, San Mateo, San Bruno and around Angel Island.[101] The founder of Fort Ross, Ivan Kuskov, finding otters scarce on his second voyage to Bodega Bay in 1812, sent a party of Aleuts to San Francisco Bay, where they met another Russian party and an American party, and caught 1,160 sea otters in three months.[124] By 1817, sea otters in the area were practically eliminated and the Russians sought permission from the Spanish and the Mexican governments to hunt further and further south of San Francisco.[125] In 1833, fur trappers George Nidever and George Yount canoed "along the Petaluma side of [the] Bay, and then proceeded to the San Joaquin River", returning with sea otter, beaver, and river otter pelts.[126] Remnant sea otter populations may have survived in the bay until 1840, when the Rancho Punta de Quentin was granted to Captain John B. R. Cooper, a sea captain from Boston, by Mexican Governor Juan Bautista Alvarado along with a license to hunt sea otters, reportedly then prevalent at the mouth of Corte Madera Creek.[127]
In the late 1980s, the USFWS relocated about 140 southern sea otters to San Nicolas Island in southern California, in the hope of establishing a reserve population should the mainland be struck by an oil spill. To the surprise of biologists, the majority of the San Nicolas sea otters swam back to the mainland.[128] Another group of twenty swam 74 miles (119 km) north to San Miguel Island, where they were captured and removed.[129] By 2005, only 30 sea otters remained at San Nicolas,[130] although they were slowly increasing as they thrived on the abundant prey around the island.[128] The plan that authorized the translocation program had predicted the carrying capacity would be reached within five to 10 years.[131] The spring 2016 count at San Nicolas Island was 104 sea otters, continuing a 5-year positive trend of over 12% per year.[132] Sea otters were observed twice in Southern California in 2011, once near Laguna Beach and once at Zuniga Point Jetty, near San Diego. These are the first documented sightings of otters this far south in 30 years.[133]
When the USFWS implemented the translocation program, it also attempted, in 1986, to implement "zonal management" of the Californian population. To manage the competition between sea otters and fisheries, it declared an "otter-free zone" stretching from Point Conception to the Mexican border. In this zone, only San Nicolas Island was designated as sea otter habitat, and sea otters found elsewhere in the area were supposed to be captured and relocated. These plans were abandoned after many translocated otters died and also as it proved impractical to capture the hundreds of otters which ignored regulations and swam into the zone.[134] However, after engaging in a period of public commentary in 2005, the Fish and Wildlife Service failed to release a formal decision on the issue.[130] Then, in response to lawsuits filed by the Santa Barbara-based Environmental Defense Center and the Otter Project, on 19 December 2012 the USFWS declared that the "no otter zone" experiment was a failure, and will protect the otters re-colonizing the coast south of Point Conception as threatened species.[135] Although abalone fisherman blamed the incursions of sea otters for the decline of abalone, commercial abalone fishing in southern California came to an end from overfishing in 1997, years before significant otter moved south of Point Conception. In addition, white abalone (Haliotis sorenseni), a species never overlapping with sea otter, had declined in numbers 99% by 1996, and became the first marine invertebrate to be federally listed as endangered.[136]
Although the southern sea otter's range has continuously expanded from the remnant population of about 50 individuals in Big Sur since protection in 1911, from 2007 to 2010, the otter population and its range contracted and since 2010 has made little progress.[137][138] As of spring 2010, the northern boundary had moved from about Tunitas Creek to a point 2 kilometres (1.2 mi) southeast of Pigeon Point, and the southern boundary has moved along the Gaviota Coast from approximately Coal Oil Point to Gaviota State Park.[139] A toxin called microcystin, produced by a type of cyanobacteria (Microcystis), seems to be concentrated in the shellfish the otters eat, poisoning them. Cyanobacteria are found in stagnant water enriched with nitrogen and phosphorus from septic tank and agricultural fertilizer runoff, and may be flushed into the ocean when streamflows are high in the rainy season.[140][141] A record number of sea otter carcasses were found on California's coastline in 2010, with increased shark attacks an increasing component of the mortality.[142] Great white sharks do not consume relatively fat-poor sea otters but shark-bitten carcasses have increased from 8% in the 1980s to 15% in the 1990s and to 30% in 2010 and 2011.[143]
For southern sea otters to be considered for removal from threatened species listing, the U.S. Fish and Wildlife Service (USFWS) determined that the population should exceed 3,090 for three consecutive years.[137] In response to recovery efforts, the population climbed steadily from the mid-20th century through the early 2000s, then remained relatively flat from 2005 to 2014 at just under 3,000. There was some contraction from the northern (now Pigeon Point) and southern limits of the sea otter's range during the end of this period, circumstantially related to an increase in lethal shark bites, raising concerns that the population had reached a plateau.[144] However, the population increased markedly from 2015 to 2016, with the United States Geological Survey (USGS) California sea otter survey 3-year average reaching 3,272 in 2016, the first time it exceeded the threshold for delisting from the Endangered Species Act (ESA).[132] If populations continued to grow and ESA delisting occurred, southern sea otters would still be fully protected by state regulations and the Marine Mammal Protection Act, which set higher thresholds for protection, at approximately 8,400 individuals.[145] However, ESA delisting seems unlikely due to a precipitous population decline recorded in the spring 2017 USGS sea otter survey count, from the 2016 high of 3,615 individuals to 2,688, a loss of 25% of the California sea otter population.[146]
Mexico
Historian Adele Ogden described sea otters are particularly abundant in "Lower California", now the Baja California Peninsula, where "seven bays...were main centers". The southernmost limit was Punta Morro Hermoso about 21+1⁄2 miles (34.6 km) south of Punta Eugenia, in turn a headland at the southwestern end of Sebastián Vizcaíno Bay, on the west coast of the Baja Peninsula. Otter were also taken from San Benito Island, Cedros Island, and Isla Natividad in the Bay.[101] By the early 1900s, Baja's sea otters were extirpated by hunting. In a 1997 survey, small numbers of sea otters, including pups, were reported by local fishermen, but scientists could not confirm these accounts.[147] However, male and female otters have been confirmed by scientists off shores of the Baja Peninsula in a 2014 study, who hypothesize that otter dispersed there beginning in 2005. These sea otters may have dispersed from San Nicolas Island, which is 300 kilometres (190 mi) away, as individuals have been recorded traversing distances of over 800 kilometres (500 mi). Genetic analysis of most of these animals were consistent with California, i.e. United States, otter origins, however one otter had a haplotype not previously reported, and could represent a remnant of the original native Mexican otter population.[148]
Ecology
Diet
High energetic requirements of sea otter metabolism require them to consume at least 20% of their body weight a day.[31] Surface swimming and foraging are major factors in their high energy expenditure due to drag on the surface of the water when swimming and the thermal heat loss from the body during deep dives when foraging.[149][31] Sea otter muscles are specially adapted to generate heat without physical activity.[150]
Sea otters consume over 100 prey species.[151] In most of its range, the sea otter's diet consists almost exclusively of marine benthic invertebrates, including sea urchins (such as Strongylocentrotus franciscanus and S. purpuratus), fat innkeeper worms, a variety of bivalves such as clams, mussels (such as Mytilus edulis), and scallops (such as Crassadoma gigantea), abalone, limpets (such as Diodora aspera), chitons (such as Katharina tunicata), other mollusks, crustaceans, and snails.[151][152][153] Its prey ranges in size from tiny limpets and crabs to giant octopuses.[151] Where prey such as sea urchins, clams, and abalone are present in a range of sizes, sea otters tend to select larger items over smaller ones of similar type.[151] In California, they have been noted to ignore Pismo clams smaller than 3 inches (76 mm) across.[154]
In a few northern areas, fish are also eaten. In studies performed at Amchitka Island in the 1960s, where the sea otter population was at carrying capacity, 50% of food found in sea otter stomachs was fish.[155] The fish species were usually bottom-dwelling and sedentary or sluggish forms, such as Hemilepidotus hemilepidotus and family Tetraodontidae.[155] However, south of Alaska on the North American coast, fish are a negligible or extremely minor part of the sea otter's diet.[19][156] Contrary to popular depictions, sea otters rarely eat starfish, and any kelp that is consumed apparently passes through the sea otter's system undigested.[157]
The individuals within a particular area often differ in their foraging methods and prey types, and tend to follow the same patterns as their mothers.[158] The diet of local populations also changes over time, as sea otters can significantly deplete populations of highly preferred prey such as large sea urchins, and prey availability is also affected by other factors such as fishing by humans.[19] Sea otters can thoroughly remove abalone from an area except for specimens in deep rock crevices,[159] however, they never completely wipe out a prey species from an area.[160] A 2007 Californian study demonstrated, in areas where food was relatively scarce, a wider variety of prey was consumed. Surprisingly, though, the diets of individuals were more specialized in these areas than in areas where food was plentiful.[128]
As a keystone species
Sea otters control herbivore populations, ensuring sufficient coverage of kelp in kelp forests
Sea otters are a classic example of a keystone species; their presence affects the ecosystem more profoundly than their size and numbers would suggest. They keep the population of certain benthic (sea floor) herbivores, particularly sea urchins, in check.[4] Sea urchins graze on the lower stems of kelp, causing the kelp to drift away and die.[161] Loss of the habitat and nutrients provided by kelp forests leads to profound cascade effects on the marine ecosystem. North Pacific areas that do not have sea otters often turn into urchin barrens, with abundant sea urchins and no kelp forest.[6] Kelp forests are extremely productive ecosystems. Kelp forests sequester (absorb and capture) CO2 from the atmosphere through photosynthesis. Sea otters may help mitigate effects of climate change by their cascading trophic influence[162]
Reintroduction of sea otters to British Columbia has led to a dramatic improvement in the health of coastal ecosystems,[163] and similar changes have been observed as sea otter populations recovered in the Aleutian and Commander Islands and the Big Sur coast of California[164] However, some kelp forest ecosystems in California have also thrived without sea otters, with sea urchin populations apparently controlled by other factors.[164] The role of sea otters in maintaining kelp forests has been observed to be more important in areas of open coast than in more protected bays and estuaries.[164]
Sea otters affect rocky ecosystems that are dominated by mussel beds by removing mussels from rocks. This allows space for competing species and increases species diversity.[164]
Predators
Leading mammalian predators of this species include orcas and sea lions, and bald eagles may grab pups from the surface of the water. Young predators may kill an otter and not eat it.[67] On land, young sea otters may face attack from bears and coyotes. In California, great white sharks are their primary predator.[165] In Katmai National Park, grey wolves have been recorded to hunt and kill sea otters.[166]
Urban runoff transporting cat feces into the ocean brings Toxoplasma gondii, an obligate parasite of felids, which has killed sea otters.[167] Parasitic infections of Sarcocystis neurona are also associated with human activity.[16] According to the U.S. Geological Survey and the CDC, northern sea otters off Washington have been infected with the H1N1 flu virus and "may be a newly identified animal host of influenza viruses".[168]
Relationship with humans
Fur trade
Aleut men in Unalaska in 1896 used waterproof kayak gear and garments to hunt sea otters.
Sea otters have the thickest fur of any mammal, which makes them a common target for many hunters. Archaeological evidence indicates that for thousands of years, indigenous peoples have hunted sea otters for food and fur. Large-scale hunting, part of the Maritime Fur Trade, which would eventually kill approximately one million sea otters, began in the 18th century when hunters and traders began to arrive from all over the world to meet foreign demand for otter pelts, which were one of the world's most valuable types of fur.[22]
In the early 18th century, Russians began to hunt sea otters in the Kuril Islands[22] and sold them to the Chinese at Kyakhta. Russia was also exploring the far northern Pacific at this time, and sent Vitus Bering to map the Arctic coast and find routes from Siberia to North America. In 1741, on his second North Pacific voyage, Bering was shipwrecked off Bering Island in the Commander Islands, where he and many of his crew died. The surviving crew members, which included naturalist Georg Steller, discovered sea otters on the beaches of the island and spent the winter hunting sea otters and gambling with otter pelts. They returned to Siberia, having killed nearly 1,000 sea otters, and were able to command high prices for the pelts.[169] Thus began what is sometimes called the "Great Hunt", which would continue for another hundred years. The Russians found the sea otter far more valuable than the sable skins that had driven and paid for most of their expansion across Siberia. If the sea otter pelts brought back by Bering's survivors had been sold at Kyakhta prices they would have paid for one tenth the cost of Bering's expedition.[170]
Pelt sales (in thousands) in the London fur market – the decline beginning in the 1880s reflects dwindling sea otter populations.[171]
Russian fur-hunting expeditions soon depleted the sea otter populations in the Commander Islands, and by 1745, they began to move on to the Aleutian Islands. The Russians initially traded with the Aleuts inhabitants of these islands for otter pelts, but later enslaved the Aleuts, taking women and children hostage and torturing and killing Aleut men to force them to hunt. Many Aleuts were either murdered by the Russians or died from diseases the hunters had introduced.[172][disputed – discuss] The Aleut population was reduced, by the Russians' own estimate, from 20,000 to 2,000.[173] By the 1760s, the Russians had reached Alaska. In 1799, Tsar Paul I consolidated the rival fur-hunting companies into the Russian-American Company, granting it an imperial charter and protection, and a monopoly over trade rights and territorial acquisition. Under Aleksander I, the administration of the merchant-controlled company was transferred to the Imperial Navy, largely due to the alarming reports by naval officers of native abuse; in 1818, the indigenous peoples of Alaska were granted civil rights equivalent to a townsman status in the Russian Empire.[174]
Other nations joined in the hunt in the south. Along the coasts of what is now Mexico and California, Spanish explorers bought sea otter pelts from Native Americans and sold them in Asia.[172] In 1778, British explorer Captain James Cook reached Vancouver Island and bought sea otter furs from the First Nations people. When Cook's ship later stopped at a Chinese port, the pelts rapidly sold at high prices, and were soon known as "soft gold". As word spread, people from all over Europe and North America began to arrive in the Pacific Northwest to trade for sea otter furs.[175]
Russian hunting expanded to the south, initiated by American ship captains, who subcontracted Russian supervisors and Aleut hunters[176] in what are now Washington, Oregon, and California. Between 1803 and 1846, 72 American ships were involved in the otter hunt in California, harvesting an estimated 40,000 skins and tails, compared to only 13 ships of the Russian-American Company, which reported 5,696 otter skins taken between 1806 and 1846.[177] In 1812, the Russians founded an agricultural settlement at what is now Fort Ross in northern California, as their southern headquarters.[175] Eventually, sea otter populations became so depleted, commercial hunting was no longer viable. It had stopped in the Aleutian Islands, by 1808, as a conservation measure imposed by the Russian-American Company. Further restrictions were ordered by the company in 1834.[178] When Russia sold Alaska to the United States in 1867, the Alaska population had recovered to over 100,000, but Americans resumed hunting and quickly extirpated the sea otter again.[179] Prices rose as the species became rare. During the 1880s, a pelt brought $105 to $165 in the London market, but by 1903, a pelt could be worth as much as $1,125.[79] In 1911, Russia, Japan, Great Britain (for Canada) and the United States signed the Treaty for the Preservation and Protection of Fur Seals, imposing a moratorium on the harvesting of sea otters.[180] So few remained, perhaps only 1,000–2,000 individuals in the wild, that many believed the species would become extinct.[19]
Recovery and conservation
Main article: Sea otter conservation
In the wake of the March 1989 Exxon Valdez oil spill, heavy sheens of oil covered large areas of Prince William Sound.
During the 20th century, sea otter numbers rebounded in about two-thirds of their historic range, a recovery considered one of the greatest successes in marine conservation.[181] However, the IUCN still lists the sea otter as an endangered species, and describes the significant threats to sea otters as oil pollution, predation by orcas, poaching, and conflicts with fisheries – sea otters can drown if entangled in fishing gear.[1] The hunting of sea otters is no longer legal except for limited harvests by indigenous peoples in the United States.[182] Poaching was a serious concern in the Russian Far East immediately after the collapse of the Soviet Union in 1991; however, it has declined significantly with stricter law enforcement and better economic conditions.[108]
The most significant threat to sea otters is oil spills,[67] to which they are particularly vulnerable, since they rely on their fur to keep warm. When their fur is soaked with oil, it loses its ability to retain air, and the animals can quickly die from hypothermia.[67] The liver, kidneys, and lungs of sea otters also become damaged after they inhale oil or ingest it when grooming.[67] The Exxon Valdez oil spill of 24 March 1989 killed thousands of sea otters in Prince William Sound, and as of 2006, the lingering oil in the area continues to affect the population.[183] Describing the public sympathy for sea otters that developed from media coverage of the event, a U.S. Fish and Wildlife Service spokesperson wrote:
As a playful, photogenic, innocent bystander, the sea otter epitomized the role of victim ... cute and frolicsome sea otters suddenly in distress, oiled, frightened, and dying, in a losing battle with the oil.[19]
The small geographic ranges of the sea otter populations in California, Washington, and British Columbia mean a single major spill could be catastrophic for that state or province.[19][57][63] Prevention of oil spills and preparation to rescue otters if one happens is a major focus for conservation efforts. Increasing the size and range of sea otter populations would also reduce the risk of an oil spill wiping out a population.[19] However, because of the species' reputation for depleting shellfish resources, advocates for commercial, recreational, and subsistence shellfish harvesting have often opposed allowing the sea otter's range to increase, and there have even been instances of fishermen and others illegally killing them.[184]
In the Aleutian Islands, a massive and unexpected disappearance of sea otters has occurred in recent decades. In the 1980s, the area was home to an estimated 55,000 to 100,000 sea otters, but the population fell to around 6,000 animals by 2000.[185] The most widely accepted, but still controversial, hypothesis is that killer whales have been eating the otters. The pattern of disappearances is consistent with a rise in predation, but there has been no direct evidence of orcas preying on sea otters to any significant extent.[114]
Another area of concern is California, where recovery began to fluctuate or decline in the late 1990s.[186] Unusually high mortality rates amongst adult and subadult otters, particularly females, have been reported.[106] In 2017 the US Geological Survey found a 3% drop in the sea otter population of the California coast. This number still keeps them on track for removal from the endangered species list, although just barely.[187] Necropsies of dead sea otters indicate diseases, particularly Toxoplasma gondii and acanthocephalan parasite infections, are major causes of sea otter mortality in California.[188] The Toxoplasma gondii parasite, which is often fatal to sea otters, is carried by wild and domestic cats and may be transmitted by domestic cat droppings flushed into the ocean via sewage systems.[188][189] Although disease has clearly contributed to the deaths of many of California's sea otters, it is not known why the California population is apparently more affected by disease than populations in other areas.[188]
Sea otters off the coast of Washington, within the Olympic Coast National Marine Sanctuary
Sea otter habitat is preserved through several protected areas in the United States, Russia and Canada. In marine protected areas, polluting activities such as dumping of waste and oil drilling are typically prohibited.[190] An estimated 1,200 sea otters live within the Monterey Bay National Marine Sanctuary, and more than 500 live within the Olympic Coast National Marine Sanctuary.[191][192]
Economic impact
Some of the sea otter's preferred prey species, particularly abalone, clams, and crabs, are also food sources for humans. In some areas, massive declines in shellfish harvests have been blamed on the sea otter, and intense public debate has taken place over how to manage the competition between sea otters and humans for seafood.[193]
The debate is complicated because sea otters have sometimes been held responsible for declines of shellfish stocks that were more likely caused by overfishing, disease, pollution, and seismic activity.[63][194] Shellfish declines have also occurred in many parts of the North American Pacific coast that do not have sea otters, and conservationists sometimes note the existence of large concentrations of shellfish on the coast is a recent development resulting from the fur trade's near-extirpation of the sea otter.[194] Although many factors affect shellfish stocks, sea otter predation can deplete a fishery to the point where it is no longer commercially viable.[193] Scientists agree that sea otters and abalone fisheries cannot exist in the same area,[193] and the same is likely true for certain other types of shellfish, as well.[185]
Many facets of the interaction between sea otters and the human economy are not as immediately felt. Sea otters have been credited with contributing to the kelp harvesting industry via their well-known role in controlling sea urchin populations; kelp is used in the production of diverse food and pharmaceutical products.[195] Although human divers harvest red sea urchins both for food and to protect the kelp, sea otters hunt more sea urchin species and are more consistently effective in controlling these populations.[196] E. lutris is a controlling predator of the red king crab (Paralithodes camtschaticus) in the Bering Sea, which would otherwise be out of control as it is in its invasive range, the Barents Sea.[197] (Berents otters, Lutra lutra, occupy the same ecological niche and so are believed to help to control them in the Berents but this has not been studied.)[197] The health of the kelp forest ecosystem is significant in nurturing populations of fish, including commercially important fish species.[195] In some areas, sea otters are popular tourist attractions, bringing visitors to local hotels, restaurants, and sea otter-watching expeditions.[195]
Roles in human cultures
Aleut carving of a sea otter hunt
Left: Aleut sea otter amulet in the form of a mother with pup. Above: Aleut carving of a sea otter hunt on a whalebone spear. Both items are on display at the Peter the Great Museum of Anthropology and Ethnography in St. Petersburg. Articles depicting sea otters were considered to have magical properties.[198]
For many maritime indigenous cultures throughout the North Pacific, especially the Ainu in the Kuril Islands, the Koryaks and Itelmen of Kamchatka, the Aleut in the Aleutian Islands, the Haida of Haida Gwaii[199] and a host of tribes on the Pacific coast of North America, the sea otter has played an important role as a cultural, as well as material, resource. In these cultures, many of which have strongly animist traditions full of legends and stories in which many aspects of the natural world are associated with spirits, the sea otter was considered particularly kin to humans. The Nuu-chah-nulth, Haida, and other First Nations of coastal British Columbia used the warm and luxurious pelts as chiefs' regalia. Sea otter pelts were given in potlatches to mark coming-of-age ceremonies, weddings, and funerals.[68] The Aleuts carved sea otter bones for use as ornaments and in games, and used powdered sea otter baculum as a medicine for fever.[200]
Among the Ainu, the otter is portrayed as an occasional messenger between humans and the creator.[201] The sea otter is a recurring figure in Ainu folklore. A major Ainu epic, the Kutune Shirka, tells the tale of wars and struggles over a golden sea otter. Versions of a widespread Aleut legend tell of lovers or despairing women who plunge into the sea and become otters.[202] These links have been associated with the many human-like behavioral features of the sea otter, including apparent playfulness, strong mother-pup bonds and tool use, yielding to ready anthropomorphism.[203] The beginning of commercial exploitation had a great impact on the human, as well as animal, populations. The Ainu and Aleuts have been displaced or their numbers are dwindling, while the coastal tribes of North America, where the otter is in any case greatly depleted, no longer rely as intimately on sea mammals for survival.[204]
Since the mid-1970s, the beauty and charisma of the species have gained wide appreciation, and the sea otter has become an icon of environmental conservation.[186] The round, expressive face and soft, furry body of the sea otter are depicted in a wide variety of souvenirs, postcards, clothing, and stuffed toys.[205]
Aquariums and zoos
Sea otters can do well in captivity, and are featured in over 40 public aquariums and zoos.[206] The Seattle Aquarium became the first institution to raise sea otters from conception to adulthood with the birth of Tichuk in 1979, followed by three more pups in the early 1980s.[207] In 2007, a YouTube video of two sea otters holding paws drew 1.5 million viewers in two weeks, and had over 22 million views as of July 2022.[208] Filmed five years previously at the Vancouver Aquarium, it was YouTube's most popular animal video at the time, although it has since been surpassed. The lighter-colored otter in the video is Nyac, a survivor of the 1989 Exxon Valdez oil spill.[209] Nyac died in September 2008, at the age of 20.[210] Milo, the darker one, died of lymphoma in January 2012.[211]
Current conservation
Sea otters, being a known keystone species, need a humanitarian effort to be protected from endangerment through "unregulated human exploitation".[212] This species has increasingly been impacted by the large oil spills and environmental degradation caused by overfishing and entanglement in fishing gear.[213] Current efforts have been made in legislation: the international Fur Seal Treaty, The Endangered Species Act, IUCN/The World Conservation Union, Convention on international Trade in Endangered Species of Wild Fauna and Flora, and the Marine Mammal Protection Act of 1972. Other conservation efforts are done through reintroduction and zoological parks. Wikipedia
Fish, any of approximately 34,000 species of vertebrate animals (phylum Chordata) found in the fresh and salt waters of the world. Living species range from the primitive jawless lampreys and hagfishes through the cartilaginous sharks, skates, and rays to the abundant and diverse bony fishes. Most fish species are cold-blooded; however, one species, the opah (Lampris guttatus), is warm-blooded.
The term fish is applied to a variety of vertebrates of several evolutionary lines. It describes a life-form rather than a taxonomic group. As members of the phylum Chordata, fish share certain features with other vertebrates. These features are gill slits at some point in the life cycle, a notochord, or skeletal supporting rod, a dorsal hollow nerve cord, and a tail. Living fishes represent some five classes, which are as distinct from one another as are the four classes of familiar air-breathing animals—amphibians, reptiles, birds, and mammals. For example, the jawless fishes (Agnatha) have gills in pouches and lack limb girdles. Extant agnathans are the lampreys and the hagfishes. As the name implies, the skeletons of fishes of the class Chondrichthyes (from chondr, “cartilage,” and ichthyes, “fish”) are made entirely of cartilage. Modern fish of this class lack a swim bladder, and their scales and teeth are made up of the same placoid material. Sharks, skates, and rays are examples of cartilaginous fishes. The bony fishes are by far the largest class. Examples range from the tiny seahorse to the 450-kg (1,000-pound) blue marlin, from the flattened soles and flounders to the boxy puffers and ocean sunfishes. Unlike the scales of the cartilaginous fishes, those of bony fishes, when present, grow throughout life and are made up of thin overlapping plates of bone. Bony fishes also have an operculum that covers the gill slits.
The study of fishes, the science of ichthyology, is of broad importance. Fishes are of interest to humans for many reasons, the most important being their relationship with and dependence on the environment. A more obvious reason for interest in fishes is their role as a moderate but important part of the world’s food supply. This resource, once thought unlimited, is now realized to be finite and in delicate balance with the biological, chemical, and physical factors of the aquatic environment. Overfishing, pollution, and alteration of the environment are the chief enemies of proper fisheries management, both in fresh waters and in the ocean. (For a detailed discussion of the technology and economics of fisheries, see commercial fishing.) Another practical reason for studying fishes is their use in disease control. As predators on mosquito larvae, they help curb malaria and other mosquito-borne diseases.
Fishes are valuable laboratory animals in many aspects of medical and biological research. For example, the readiness of many fishes to acclimate to captivity has allowed biologists to study behaviour, physiology, and even ecology under relatively natural conditions. Fishes have been especially important in the study of animal behaviour, where research on fishes has provided a broad base for the understanding of the more flexible behaviour of the higher vertebrates. The zebra fish is used as a model in studies of gene expression.
There are aesthetic and recreational reasons for an interest in fishes. Millions of people keep live fishes in home aquariums for the simple pleasure of observing the beauty and behaviour of animals otherwise unfamiliar to them. Aquarium fishes provide a personal challenge to many aquarists, allowing them to test their ability to keep a small section of the natural environment in their homes. Sportfishing is another way of enjoying the natural environment, also indulged in by millions of people every year. Interest in aquarium fishes and sportfishing supports multimillion-dollar industries throughout the world.
Fishes have been in existence for more than 450 million years, during which time they have evolved repeatedly to fit into almost every conceivable type of aquatic habitat. In a sense, land vertebrates are simply highly modified fishes: when fishes colonized the land habitat, they became tetrapod (four-legged) land vertebrates. The popular conception of a fish as a slippery, streamlined aquatic animal that possesses fins and breathes by gills applies to many fishes, but far more fishes deviate from that conception than conform to it. For example, the body is elongate in many forms and greatly shortened in others; the body is flattened in some (principally in bottom-dwelling fishes) and laterally compressed in many others; the fins may be elaborately extended, forming intricate shapes, or they may be reduced or even lost; and the positions of the mouth, eyes, nostrils, and gill openings vary widely. Air breathers have appeared in several evolutionary lines.
Many fishes are cryptically coloured and shaped, closely matching their respective environments; others are among the most brilliantly coloured of all organisms, with a wide range of hues, often of striking intensity, on a single individual. The brilliance of pigments may be enhanced by the surface structure of the fish, so that it almost seems to glow. A number of unrelated fishes have actual light-producing organs. Many fishes are able to alter their coloration—some for the purpose of camouflage, others for the enhancement of behavioral signals.
Fishes range in adult length from less than 10 mm (0.4 inch) to more than 20 metres (60 feet) and in weight from about 1.5 grams (less than 0.06 ounce) to many thousands of kilograms. Some live in shallow thermal springs at temperatures slightly above 42 °C (100 °F), others in cold Arctic seas a few degrees below 0 °C (32 °F) or in cold deep waters more than 4,000 metres (13,100 feet) beneath the ocean surface. The structural and, especially, the physiological adaptations for life at such extremes are relatively poorly known and provide the scientifically curious with great incentive for study.
Almost all natural bodies of water bear fish life, the exceptions being very hot thermal ponds and extremely salt-alkaline lakes, such as the Dead Sea in Asia and the Great Salt Lake in North America. The present distribution of fishes is a result of the geological history and development of Earth as well as the ability of fishes to undergo evolutionary change and to adapt to the available habitats. Fishes may be seen to be distributed according to habitat and according to geographical area. Major habitat differences are marine and freshwater. For the most part, the fishes in a marine habitat differ from those in a freshwater habitat, even in adjacent areas, but some, such as the salmon, migrate from one to the other. The freshwater habitats may be seen to be of many kinds. Fishes found in mountain torrents, Arctic lakes, tropical lakes, temperate streams, and tropical rivers will all differ from each other, both in obvious gross structure and in physiological attributes. Even in closely adjacent habitats where, for example, a tropical mountain torrent enters a lowland stream, the fish fauna will differ. The marine habitats can be divided into deep ocean floors (benthic), mid-water oceanic (bathypelagic), surface oceanic (pelagic), rocky coast, sandy coast, muddy shores, bays, estuaries, and others. Also, for example, rocky coastal shores in tropical and temperate regions will have different fish faunas, even when such habitats occur along the same coastline.
Although much is known about the present geographical distribution of fishes, far less is known about how that distribution came about. Many parts of the fish fauna of the fresh waters of North America and Eurasia are related and undoubtedly have a common origin. The faunas of Africa and South America are related, extremely old, and probably an expression of the drifting apart of the two continents. The fauna of southern Asia is related to that of Central Asia, and some of it appears to have entered Africa. The extremely large shore-fish faunas of the Indian and tropical Pacific oceans comprise a related complex, but the tropical shore fauna of the Atlantic, although containing Indo-Pacific components, is relatively limited and probably younger. The Arctic and Antarctic marine faunas are quite different from each other. The shore fauna of the North Pacific is quite distinct, and that of the North Atlantic more limited and probably younger. Pelagic oceanic fishes, especially those in deep waters, are similar the world over, showing little geographical isolation in terms of family groups. The deep oceanic habitat is very much the same throughout the world, but species differences do exist, showing geographical areas determined by oceanic currents and water masses.
All aspects of the life of a fish are closely correlated with adaptation to the total environment, physical, chemical, and biological. In studies, all the interdependent aspects of fish, such as behaviour, locomotion, reproduction, and physical and physiological characteristics, must be taken into account.
Correlated with their adaptation to an extremely wide variety of habitats is the extremely wide variety of life cycles that fishes display. The great majority hatch from relatively small eggs a few days to several weeks or more after the eggs are scattered in the water. Newly hatched young are still partially undeveloped and are called larvae until body structures such as fins, skeleton, and some organs are fully formed. Larval life is often very short, usually less than a few weeks, but it can be very long, some lampreys continuing as larvae for at least five years. Young and larval fishes, before reaching sexual maturity, must grow considerably, and their small size and other factors often dictate that they live in a habitat different than that of the adults. For example, most tropical marine shore fishes have pelagic larvae. Larval food also is different, and larval fishes often live in shallow waters, where they may be less exposed to predators.
After a fish reaches adult size, the length of its life is subject to many factors, such as innate rates of aging, predation pressure, and the nature of the local climate. The longevity of a species in the protected environment of an aquarium may have nothing to do with how long members of that species live in the wild. Many small fishes live only one to three years at the most. In some species, however, individuals may live as long as 10 or 20 or even 100 years.
Fish behaviour is a complicated and varied subject. As in almost all animals with a central nervous system, the nature of a response of an individual fish to stimuli from its environment depends upon the inherited characteristics of its nervous system, on what it has learned from past experience, and on the nature of the stimuli. Compared with the variety of human responses, however, that of a fish is stereotyped, not subject to much modification by “thought” or learning, and investigators must guard against anthropomorphic interpretations of fish behaviour.
Fishes perceive the world around them by the usual senses of sight, smell, hearing, touch, and taste and by special lateral line water-current detectors. In the few fishes that generate electric fields, a process that might best be called electrolocation aids in perception. One or another of these senses often is emphasized at the expense of others, depending upon the fish’s other adaptations. In fishes with large eyes, the sense of smell may be reduced; others, with small eyes, hunt and feed primarily by smell (such as some eels).
Specialized behaviour is primarily concerned with the three most important activities in the fish’s life: feeding, reproduction, and escape from enemies. Schooling behaviour of sardines on the high seas, for instance, is largely a protective device to avoid enemies, but it is also associated with and modified by their breeding and feeding requirements. Predatory fishes are often solitary, lying in wait to dart suddenly after their prey, a kind of locomotion impossible for beaked parrot fishes, which feed on coral, swimming in small groups from one coral head to the next. In addition, some predatory fishes that inhabit pelagic environments, such as tunas, often school.
Sleep in fishes, all of which lack true eyelids, consists of a seemingly listless state in which the fish maintains its balance but moves slowly. If attacked or disturbed, most can dart away. A few kinds of fishes lie on the bottom to sleep. Most catfishes, some loaches, and some eels and electric fishes are strictly nocturnal, being active and hunting for food during the night and retiring during the day to holes, thick vegetation, or other protective parts of the environment.
Communication between members of a species or between members of two or more species often is extremely important, especially in breeding behaviour (see below Reproduction). The mode of communication may be visual, as between the small so-called cleaner fish and a large fish of a very different species. The larger fish often allows the cleaner to enter its mouth to remove gill parasites. The cleaner is recognized by its distinctive colour and actions and therefore is not eaten, even if the larger fish is normally a predator. Communication is often chemical, signals being sent by specific chemicals called pheromones.
Many fishes have a streamlined body and swim freely in open water. Fish locomotion is closely correlated with habitat and ecological niche (the general position of the animal to its environment).
Many fishes in both marine and fresh waters swim at the surface and have mouths adapted to feed best (and sometimes only) at the surface. Often such fishes are long and slender, able to dart at surface insects or at other surface fishes and in turn to dart away from predators; needlefishes, halfbeaks, and topminnows (such as killifish and mosquito fish) are good examples. Oceanic flying fishes escape their predators by gathering speed above the water surface, with the lower lobe of the tail providing thrust in the water. They then glide hundreds of yards on enlarged, winglike pectoral and pelvic fins. South American freshwater flying fishes escape their enemies by jumping and propelling their strongly keeled bodies out of the water.
So-called mid-water swimmers, the most common type of fish, are of many kinds and live in many habitats. The powerful fusiform tunas and the trouts, for example, are adapted for strong, fast swimming, the tunas to capture prey speedily in the open ocean and the trouts to cope with the swift currents of streams and rivers. The trout body form is well adapted to many habitats. Fishes that live in relatively quiet waters such as bays or lake shores or slow rivers usually are not strong, fast swimmers but are capable of short, quick bursts of speed to escape a predator. Many of these fishes have their sides flattened, examples being the sunfish and the freshwater angelfish of aquarists. Fish associated with the bottom or substrate usually are slow swimmers. Open-water plankton-feeding fishes almost always remain fusiform and are capable of rapid, strong movement (for example, sardines and herrings of the open ocean and also many small minnows of streams and lakes).
Bottom-living fishes are of many kinds and have undergone many types of modification of their body shape and swimming habits. Rays, which evolved from strong-swimming mid-water sharks, usually stay close to the bottom and move by undulating their large pectoral fins. Flounders live in a similar habitat and move over the bottom by undulating the entire body. Many bottom fishes dart from place to place, resting on the bottom between movements, a motion common in gobies. One goby relative, the mudskipper, has taken to living at the edge of pools along the shore of muddy mangrove swamps. It escapes its enemies by flipping rapidly over the mud, out of the water. Some catfishes, synbranchid eels, the so-called climbing perch, and a few other fishes venture out over damp ground to find more promising waters than those that they left. They move by wriggling their bodies, sometimes using strong pectoral fins; most have accessory air-breathing organs. Many bottom-dwelling fishes live in mud holes or rocky crevices. Marine eels and gobies commonly are found in such habitats and for the most part venture far beyond their cavelike homes. Some bottom dwellers, such as the clingfishes (Gobiesocidae), have developed powerful adhesive disks that enable them to remain in place on the substrate in areas such as rocky coasts, where the action of the waves is great.
The methods of reproduction in fishes are varied, but most fishes lay a large number of small eggs, fertilized and scattered outside of the body. The eggs of pelagic fishes usually remain suspended in the open water. Many shore and freshwater fishes lay eggs on the bottom or among plants. Some have adhesive eggs. The mortality of the young and especially of the eggs is very high, and often only a few individuals grow to maturity out of hundreds, thousands, and in some cases millions of eggs laid.
Males produce sperm, usually as a milky white substance called milt, in two (sometimes one) testes within the body cavity. In bony fishes a sperm duct leads from each testis to a urogenital opening behind the vent or anus. In sharks and rays and in cyclostomes the duct leads to a cloaca. Sometimes the pelvic fins are modified to help transmit the milt to the eggs at the female’s vent or on the substrate where the female has placed them. Sometimes accessory organs are used to fertilize females internally—for example, the claspers of many sharks and rays.
In the females the eggs are formed in two ovaries (sometimes only one) and pass through the ovaries to the urogenital opening and to the outside. In some fishes the eggs are fertilized internally but are shed before development takes place. Members of about a dozen families each of bony fishes (teleosts) and sharks bear live young. Many skates and rays also bear live young. In some bony fishes the eggs simply develop within the female, the young emerging when the eggs hatch (ovoviviparous). Others develop within the ovary and are nourished by ovarian tissues after hatching (viviparous). There are also other methods utilized by fishes to nourish young within the female. In all live-bearers the young are born at a relatively large size and are few in number. In one family of primarily marine fishes, the surfperches from the Pacific coast of North America, Japan, and Korea, the males of at least one species are born sexually mature, although they are not fully grown.
Some fishes are hermaphroditic—an individual producing both sperm and eggs, usually at different stages of its life. Self-fertilization, however, is probably rare.
Successful reproduction and, in many cases, defense of the eggs and the young are assured by rather stereotypical but often elaborate courtship and parental behaviour, either by the male or the female or both. Some fishes prepare nests by hollowing out depressions in the sand bottom (cichlids, for example), build nests with plant materials and sticky threads excreted by the kidneys (sticklebacks), or blow a cluster of mucus-covered bubbles at the water surface (gouramis). The eggs are laid in these structures. Some varieties of cichlids and catfishes incubate eggs in their mouths.
Some fishes, such as salmon, undergo long migrations from the ocean and up large rivers to spawn in the gravel beds where they themselves hatched (anadromous fishes). Some, such as the freshwater eels (family Anguillidae), live and grow to maturity in fresh water and migrate to the sea to spawn (catadromous fishes). Other fishes undertake shorter migrations from lakes into streams, within the ocean, or enter spawning habitats that they do not ordinarily occupy in other ways.
The basic structure and function of the fish body are similar to those of all other vertebrates. The usual four types of tissues are present: surface or epithelial, connective (bone, cartilage, and fibrous tissues, as well as their derivative, blood), nerve, and muscle tissues. In addition, the fish’s organs and organ systems parallel those of other vertebrates.
The typical fish body is streamlined and spindle-shaped, with an anterior head, a gill apparatus, and a heart, the latter lying in the midline just below the gill chamber. The body cavity, containing the vital organs, is situated behind the head in the lower anterior part of the body. The anus usually marks the posterior termination of the body cavity and most often occurs just in front of the base of the anal fin. The spinal cord and vertebral column continue from the posterior part of the head to the base of the tail fin, passing dorsal to the body cavity and through the caudal (tail) region behind the body cavity. Most of the body is of muscular tissue, a high proportion of which is necessitated by swimming. In the course of evolution this basic body plan has been modified repeatedly into the many varieties of fish shapes that exist today.
The skeleton forms an integral part of the fish’s locomotion system, as well as serving to protect vital parts. The internal skeleton consists of the skull bones (except for the roofing bones of the head, which are really part of the external skeleton), the vertebral column, and the fin supports (fin rays). The fin supports are derived from the external skeleton but will be treated here because of their close functional relationship to the internal skeleton. The internal skeleton of cyclostomes, sharks, and rays is of cartilage; that of many fossil groups and some primitive living fishes is mostly of cartilage but may include some bone. In place of the vertebral column, the earliest vertebrates had a fully developed notochord, a flexible stiff rod of viscous cells surrounded by a strong fibrous sheath. During the evolution of modern fishes the rod was replaced in part by cartilage and then by ossified cartilage. Sharks and rays retain a cartilaginous vertebral column; bony fishes have spool-shaped vertebrae that in the more primitive living forms only partially replace the notochord. The skull, including the gill arches and jaws of bony fishes, is fully, or at least partially, ossified. That of sharks and rays remains cartilaginous, at times partially replaced by calcium deposits but never by true bone.
The supportive elements of the fins (basal or radial bones or both) have changed greatly during fish evolution. Some of these changes are described in the section below (Evolution and paleontology). Most fishes possess a single dorsal fin on the midline of the back. Many have two and a few have three dorsal fins. The other fins are the single tail and anal fins and paired pelvic and pectoral fins. A small fin, the adipose fin, with hairlike fin rays, occurs in many of the relatively primitive teleosts (such as trout) on the back near the base of the caudal fin.
The skin of a fish must serve many functions. It aids in maintaining the osmotic balance, provides physical protection for the body, is the site of coloration, contains sensory receptors, and, in some fishes, functions in respiration. Mucous glands, which aid in maintaining the water balance and offer protection from bacteria, are extremely numerous in fish skin, especially in cyclostomes and teleosts. Since mucous glands are present in the modern lampreys, it is reasonable to assume that they were present in primitive fishes, such as the ancient Silurian and Devonian agnathans. Protection from abrasion and predation is another function of the fish skin, and dermal (skin) bone arose early in fish evolution in response to this need. It is thought that bone first evolved in skin and only later invaded the cartilaginous areas of the fish’s body, to provide additional support and protection. There is some argument as to which came first, cartilage or bone, and fossil evidence does not settle the question. In any event, dermal bone has played an important part in fish evolution and has different characteristics in different groups of fishes. Several groups are characterized at least in part by the kind of bony scales they possess.
Scales have played an important part in the evolution of fishes. Primitive fishes usually had thick bony plates or thick scales in several layers of bone, enamel, and related substances. Modern teleost fishes have scales of bone, which, while still protective, allow much more freedom of motion in the body. A few modern teleosts (some catfishes, sticklebacks, and others) have secondarily acquired bony plates in the skin. Modern and early sharks possessed placoid scales, a relatively primitive type of scale with a toothlike structure, consisting of an outside layer of enamel-like substance (vitrodentine), an inner layer of dentine, and a pulp cavity containing nerves and blood vessels. Primitive bony fishes had thick scales of either the ganoid or the cosmoid type. Cosmoid scales have a hard, enamel-like outer layer, an inner layer of cosmine (a form of dentine), and then a layer of vascular bone (isopedine). In ganoid scales the hard outer layer is different chemically and is called ganoin. Under this is a cosminelike layer and then a vascular bony layer. The thin, translucent bony scales of modern fishes, called cycloid and ctenoid (the latter distinguished by serrations at the edges), lack enameloid and dentine layers.
Skin has several other functions in fishes. It is well supplied with nerve endings and presumably receives tactile, thermal, and pain stimuli. Skin is also well supplied with blood vessels. Some fishes breathe in part through the skin, by the exchange of oxygen and carbon dioxide between the surrounding water and numerous small blood vessels near the skin surface.
Skin serves as protection through the control of coloration. Fishes exhibit an almost limitless range of colours. The colours often blend closely with the surroundings, effectively hiding the animal. Many fishes use bright colours for territorial advertisement or as recognition marks for other members of their own species, or sometimes for members of other species. Many fishes can change their colour to a greater or lesser degree, by movement of pigment within the pigment cells (chromatophores). Black pigment cells (melanophores), of almost universal occurrence in fishes, are often juxtaposed with other pigment cells. When placed beneath iridocytes or leucophores (bearing the silvery or white pigment guanine), melanophores produce structural colours of blue and green. These colours are often extremely intense, because they are formed by refraction of light through the needlelike crystals of guanine. The blue and green refracted colours are often relatively pure, lacking the red and yellow rays, which have been absorbed by the black pigment (melanin) of the melanophores. Yellow, orange, and red colours are produced by erythrophores, cells containing the appropriate carotenoid pigments. Other colours are produced by combinations of melanophores, erythrophores, and iridocytes.
The major portion of the body of most fishes consists of muscles. Most of the mass is trunk musculature, the fin muscles usually being relatively small. The caudal fin is usually the most powerful fin, being moved by the trunk musculature. The body musculature is usually arranged in rows of chevron-shaped segments on each side. Contractions of these segments, each attached to adjacent vertebrae and vertebral processes, bends the body on the vertebral joint, producing successive undulations of the body, passing from the head to the tail, and producing driving strokes of the tail. It is the latter that provides the strong forward movement for most fishes.
The digestive system, in a functional sense, starts at the mouth, with the teeth used to capture prey or collect plant foods. Mouth shape and tooth structure vary greatly in fishes, depending on the kind of food normally eaten. Most fishes are predacious, feeding on small invertebrates or other fishes and have simple conical teeth on the jaws, on at least some of the bones of the roof of the mouth, and on special gill arch structures just in front of the esophagus. The latter are throat teeth. Most predacious fishes swallow their prey whole, and the teeth are used for grasping and holding prey, for orienting prey to be swallowed (head first) and for working the prey toward the esophagus. There are a variety of tooth types in fishes. Some fishes, such as sharks and piranhas, have cutting teeth for biting chunks out of their victims. A shark’s tooth, although superficially like that of a piranha, appears in many respects to be a modified scale, while that of the piranha is like that of other bony fishes, consisting of dentine and enamel. Parrot fishes have beaklike mouths with short incisor-like teeth for breaking off coral and have heavy pavementlike throat teeth for crushing the coral. Some catfishes have small brushlike teeth, arranged in rows on the jaws, for scraping plant and animal growth from rocks. Many fishes (such as the Cyprinidae or minnows) have no jaw teeth at all but have very strong throat teeth.
Some fishes gather planktonic food by straining it from their gill cavities with numerous elongate stiff rods (gill rakers) anchored by one end to the gill bars. The food collected on these rods is passed to the throat, where it is swallowed. Most fishes have only short gill rakers that help keep food particles from escaping out the mouth cavity into the gill chamber.
Once reaching the throat, food enters a short, often greatly distensible esophagus, a simple tube with a muscular wall leading into a stomach. The stomach varies greatly in fishes, depending upon the diet. In most predacious fishes it is a simple straight or curved tube or pouch with a muscular wall and a glandular lining. Food is largely digested there and leaves the stomach in liquid form.
Between the stomach and the intestine, ducts enter the digestive tube from the liver and pancreas. The liver is a large, clearly defined organ. The pancreas may be embedded in it, diffused through it, or broken into small parts spread along some of the intestine. The junction between the stomach and the intestine is marked by a muscular valve. Pyloric ceca (blind sacs) occur in some fishes at this junction and have a digestive or absorptive function or both.
The intestine itself is quite variable in length, depending upon the fish’s diet. It is short in predacious forms, sometimes no longer than the body cavity, but long in herbivorous forms, being coiled and several times longer than the entire length of the fish in some species of South American catfishes. The intestine is primarily an organ for absorbing nutrients into the bloodstream. The larger its internal surface, the greater its absorptive efficiency, and a spiral valve is one method of increasing its absorption surface.
Sharks, rays, chimaeras, lungfishes, surviving chondrosteans, holosteans, and even a few of the more primitive teleosts have a spiral valve or at least traces of it in the intestine. Most modern teleosts have increased the area of the intestinal walls by having numerous folds and villi (fingerlike projections) somewhat like those in humans. Undigested substances are passed to the exterior through the anus in most teleost fishes. In lungfishes, sharks, and rays, it is first passed through the cloaca, a common cavity receiving the intestinal opening and the ducts from the urogenital system.
Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills. The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour. Water taken in continuously through the mouth passes backward between the gill bars and over the gill filaments, where the exchange of gases takes place. The gills are protected by a gill cover in teleosts and many other fishes but by flaps of skin in sharks, rays, and some of the older fossil fish groups. The blood capillaries in the gill filaments are close to the gill surface to take up oxygen from the water and to give up excess carbon dioxide to the water.
Most modern fishes have a hydrostatic (ballast) organ, called the swim bladder, that lies in the body cavity just below the kidney and above the stomach and intestine. It originated as a diverticulum of the digestive canal. In advanced teleosts, especially the acanthopterygians, the bladder has lost its connection with the digestive tract, a condition called physoclistic. The connection has been retained (physostomous) by many relatively primitive teleosts. In several unrelated lines of fishes, the bladder has become specialized as a lung or, at least, as a highly vascularized accessory breathing organ. Some fishes with such accessory organs are obligate air breathers and will drown if denied access to the surface, even in well-oxygenated water. Fishes with a hydrostatic form of swim bladder can control their depth by regulating the amount of gas in the bladder. The gas, mostly oxygen, is secreted into the bladder by special glands, rendering the fish more buoyant; the gas is absorbed into the bloodstream by another special organ, reducing the overall buoyancy and allowing the fish to sink. Some deep-sea fishes may have oils, rather than gas, in the bladder. Other deep-sea and some bottom-living forms have much-reduced swim bladders or have lost the organ entirely.
The swim bladder of fishes follows the same developmental pattern as the lungs of land vertebrates. There is no doubt that the two structures have the same historical origin in primitive fishes. More or less intermediate forms still survive among the more primitive types of fishes, such as the lungfishes Lepidosiren and Protopterus.
The circulatory, or blood vascular, system consists of the heart, the arteries, the capillaries, and the veins. It is in the capillaries that the interchange of oxygen, carbon dioxide, nutrients, and other substances such as hormones and waste products takes place. The capillaries lead to the veins, which return the venous blood with its waste products to the heart, kidneys, and gills. There are two kinds of capillary beds: those in the gills and those in the rest of the body. The heart, a folded continuous muscular tube with three or four saclike enlargements, undergoes rhythmic contractions and receives venous blood in a sinus venosus. It passes the blood to an auricle and then into a thick muscular pump, the ventricle. From the ventricle the blood goes to a bulbous structure at the base of a ventral aorta just below the gills. The blood passes to the afferent (receiving) arteries of the gill arches and then to the gill capillaries. There waste gases are given off to the environment, and oxygen is absorbed. The oxygenated blood enters efferent (exuant) arteries of the gill arches and then flows into the dorsal aorta. From there blood is distributed to the tissues and organs of the body. One-way valves prevent backflow. The circulation of fishes thus differs from that of the reptiles, birds, and mammals in that oxygenated blood is not returned to the heart prior to distribution to the other parts of the body.
The primary excretory organ in fishes, as in other vertebrates, is the kidney. In fishes some excretion also takes place in the digestive tract, skin, and especially the gills (where ammonia is given off). Compared with land vertebrates, fishes have a special problem in maintaining their internal environment at a constant concentration of water and dissolved substances, such as salts. Proper balance of the internal environment (homeostasis) of a fish is in a great part maintained by the excretory system, especially the kidney.
The kidney, gills, and skin play an important role in maintaining a fish’s internal environment and checking the effects of osmosis. Marine fishes live in an environment in which the water around them has a greater concentration of salts than they can have inside their body and still maintain life. Freshwater fishes, on the other hand, live in water with a much lower concentration of salts than they require inside their bodies. Osmosis tends to promote the loss of water from the body of a marine fish and absorption of water by that of a freshwater fish. Mucus in the skin tends to slow the process but is not a sufficient barrier to prevent the movement of fluids through the permeable skin. When solutions on two sides of a permeable membrane have different concentrations of dissolved substances, water will pass through the membrane into the more concentrated solution, while the dissolved chemicals move into the area of lower concentration (diffusion).
The kidney of freshwater fishes is often larger in relation to body weight than that of marine fishes. In both groups the kidney excretes wastes from the body, but the kidney of freshwater fishes also excretes large amounts of water, counteracting the water absorbed through the skin. Freshwater fishes tend to lose salt to the environment and must replace it. They get some salt from their food, but the gills and skin inside the mouth actively absorb salt from water passed through the mouth. This absorption is performed by special cells capable of moving salts against the diffusion gradient. Freshwater fishes drink very little water and take in little water with their food.
Marine fishes must conserve water, and therefore their kidneys excrete little water. To maintain their water balance, marine fishes drink large quantities of seawater, retaining most of the water and excreting the salt. Most nitrogenous waste in marine fishes appears to be secreted by the gills as ammonia. Marine fishes can excrete salt by clusters of special cells (chloride cells) in the gills.
There are several teleosts—for example, the salmon—that travel between fresh water and seawater and must adjust to the reversal of osmotic gradients. They adjust their physiological processes by spending time (often surprisingly little time) in the intermediate brackish environment.
Marine hagfishes, sharks, and rays have osmotic concentrations in their blood about equal to that of seawater and so do not have to drink water nor perform much physiological work to maintain their osmotic balance. In sharks and rays the osmotic concentration is kept high by retention of urea in the blood. Freshwater sharks have a lowered concentration of urea in the blood.
Endocrine glands secrete their products into the bloodstream and body tissues and, along with the central nervous system, control and regulate many kinds of body functions. Cyclostomes have a well-developed endocrine system, and presumably it was well developed in the early Agnatha, ancestral to modern fishes. Although the endocrine system in fishes is similar to that of higher vertebrates, there are numerous differences in detail. The pituitary, the thyroid, the suprarenals, the adrenals, the pancreatic islets, the sex glands (ovaries and testes), the inner wall of the intestine, and the bodies of the ultimobranchial gland make up the endocrine system in fishes. There are some others whose function is not well understood. These organs regulate sexual activity and reproduction, growth, osmotic pressure, general metabolic activities such as the storage of fat and the utilization of foodstuffs, blood pressure, and certain aspects of skin colour. Many of these activities are also controlled in part by the central nervous system, which works with the endocrine system in maintaining the life of a fish. Some parts of the endocrine system are developmentally, and undoubtedly evolutionarily, derived from the nervous system.
As in all vertebrates, the nervous system of fishes is the primary mechanism coordinating body activities, as well as integrating these activities in the appropriate manner with stimuli from the environment. The central nervous system, consisting of the brain and spinal cord, is the primary integrating mechanism. The peripheral nervous system, consisting of nerves that connect the brain and spinal cord to various body organs, carries sensory information from special receptor organs such as the eyes, internal ears, nares (sense of smell), taste glands, and others to the integrating centres of the brain and spinal cord. The peripheral nervous system also carries information via different nerve cells from the integrating centres of the brain and spinal cord. This coded information is carried to the various organs and body systems, such as the skeletal muscular system, for appropriate action in response to the original external or internal stimulus. Another branch of the nervous system, the autonomic nervous system, helps to coordinate the activities of many glands and organs and is itself closely connected to the integrating centres of the brain.
The brain of the fish is divided into several anatomical and functional parts, all closely interconnected but each serving as the primary centre of integrating particular kinds of responses and activities. Several of these centres or parts are primarily associated with one type of sensory perception, such as sight, hearing, or smell (olfaction).
The sense of smell is important in almost all fishes. Certain eels with tiny eyes depend mostly on smell for location of food. The olfactory, or nasal, organ of fishes is located on the dorsal surface of the snout. The lining of the nasal organ has special sensory cells that perceive chemicals dissolved in the water, such as substances from food material, and send sensory information to the brain by way of the first cranial nerve. Odour also serves as an alarm system. Many fishes, especially various species of freshwater minnows, react with alarm to a chemical released from the skin of an injured member of their own species.
Many fishes have a well-developed sense of taste, and tiny pitlike taste buds or organs are located not only within their mouth cavities but also over their heads and parts of their body. Catfishes, which often have poor vision, have barbels (“whiskers”) that serve as supplementary taste organs, those around the mouth being actively used to search out food on the bottom. Some species of naturally blind cave fishes are especially well supplied with taste buds, which often cover most of their body surface.
Sight is extremely important in most fishes. The eye of a fish is basically like that of all other vertebrates, but the eyes of fishes are extremely varied in structure and adaptation. In general, fishes living in dark and dim water habitats have large eyes, unless they have specialized in some compensatory way so that another sense (such as smell) is dominant, in which case the eyes will often be reduced. Fishes living in brightly lighted shallow waters often will have relatively small but efficient eyes. Cyclostomes have somewhat less elaborate eyes than other fishes, with skin stretched over the eyeball perhaps making their vision somewhat less effective. Most fishes have a spherical lens and accommodate their vision to far or near subjects by moving the lens within the eyeball. A few sharks accommodate by changing the shape of the lens, as in land vertebrates. Those fishes that are heavily dependent upon the eyes have especially strong muscles for accommodation. Most fishes see well, despite the restrictions imposed by frequent turbidity of the water and by light refraction.
Fossil evidence suggests that colour vision evolved in fishes more than 300 million years ago, but not all living fishes have retained this ability. Experimental evidence indicates that many shallow-water fishes, if not all, have colour vision and see some colours especially well, but some bottom-dwelling shore fishes live in areas where the water is sufficiently deep to filter out most if not all colours, and these fishes apparently never see colours. When tested in shallow water, they apparently are unable to respond to colour differences.
Sound perception and balance are intimately associated senses in a fish. The organs of hearing are entirely internal, located within the skull, on each side of the brain and somewhat behind the eyes. Sound waves, especially those of low frequencies, travel readily through water and impinge directly upon the bones and fluids of the head and body, to be transmitted to the hearing organs. Fishes readily respond to sound; for example, a trout conditioned to escape by the approach of fishermen will take flight upon perceiving footsteps on a stream bank even if it cannot see a fisherman. Compared with humans, however, the range of sound frequencies heard by fishes is greatly restricted. Many fishes communicate with each other by producing sounds in their swim bladders, in their throats by rasping their teeth, and in other ways.
A fish or other vertebrate seldom has to rely on a single type of sensory information to determine the nature of the environment around it. A catfish uses taste and touch when examining a food object with its oral barbels. Like most other animals, fishes have many touch receptors over their body surface. Pain and temperature receptors also are present in fishes and presumably produce the same kind of information to a fish as to humans. Fishes react in a negative fashion to stimuli that would be painful to human beings, suggesting that they feel a sensation of pain.
An important sensory system in fishes that is absent in other vertebrates (except some amphibians) is the lateral line system. This consists of a series of heavily innervated small canals located in the skin and bone around the eyes, along the lower jaw, over the head, and down the mid-side of the body, where it is associated with the scales. Intermittently along these canals are located tiny sensory organs (pit organs) that apparently detect changes in pressure. The system allows a fish to sense changes in water currents and pressure, thereby helping the fish to orient itself to the various changes that occur in the physical environment.
quote by
Sir Julian Sorell Huxley FRS was an English evolutionary biologist, eugenicist and internationalist. He was a proponent of natural selection, and a leading figure in the mid-twentieth-century modern synthesis
digital draw via pixlr, edited via gimp
The FV4201 Chieftain was the main battle tank of the UK from its introduction in 1967. It was a radical evolutionary development of the successful Centurion line of tanks that had emerged at the end of WWII.
Chieftain was designed to be as well-protected as possible and to be equipped with a powerful 120mm rifled cannon. The heavy armour came at the price of reduced mobility, chiefly due to engine power limitations, which was perhaps the Chieftain's main drawback. The engine selected took the multi-fuel route and as introduced gave less than the planned output; improvements to the engine did not increase power to the desired value.
The Chieftain had a mantleless turret, in order to take full advantage of reclining the vehicle up to 10° in a hull-down position. To the left side of the turret was a large infra-red searchlight in an armoured housing. The suspension was of the Horstmann bogie type, with large side plates to protect the tracks and provide stand-off protection from hollow charge attack.
The main armament was the 120mm L11A5 rifled gun. This differed from most contemporary main tank armament as it used projectiles and charges which were loaded separately, as opposed to a single fixed round. The gun itself could fire a wide range of ammunition, but the most commonly loaded types were HESH or APDS.
Initially, Chieftain was equipped with a 12.7mm ranging machine-gun mounted above the main gun, firing ranging shots out to 2,400m. Later, in the late 1970s and early 1980s, a laser rangefinder replaced it, allowing engagements at much longer ranges, and also linked to the fire-control system, allowing more rapid engagements and changes of target. The gun was fully stabilised with a fully computerised integrated control system. Secondary armament consisted of a coaxial L8A1 7.62mm machine-gun, and another 7.62mm machine-gun mounted on the commander's cupola.
Like its European competitors, the Chieftain found a large export market in the Middle East, but was not adopted by any other NATO or Commonwealth countries. The Chieftains were continuously upgraded until the early 1990s when they were replaced by the Challenger series.
Chieftains were supplied to at least six countries, including Iran, Kuwait, Oman and Jordan. An agreement for sale of Chieftains to Israel was cancelled by the British Government in 1969. The largest foreign sale was to Iran, which took delivery of around 1,000 before the 1979 revolution. Further planned deliveries of the more capable 4030 series were cancelled at that point.
The tank's main combat experience was in Iranian hands during the Iran-Iraq War of 1980-88.
Seen during a demonstration in the display arena at the Tank Museum, Bovington, Dorset.
Fish, any of approximately 34,000 species of vertebrate animals (phylum Chordata) found in the fresh and salt waters of the world. Living species range from the primitive jawless lampreys and hagfishes through the cartilaginous sharks, skates, and rays to the abundant and diverse bony fishes. Most fish species are cold-blooded; however, one species, the opah (Lampris guttatus), is warm-blooded.
The term fish is applied to a variety of vertebrates of several evolutionary lines. It describes a life-form rather than a taxonomic group. As members of the phylum Chordata, fish share certain features with other vertebrates. These features are gill slits at some point in the life cycle, a notochord, or skeletal supporting rod, a dorsal hollow nerve cord, and a tail. Living fishes represent some five classes, which are as distinct from one another as are the four classes of familiar air-breathing animals—amphibians, reptiles, birds, and mammals. For example, the jawless fishes (Agnatha) have gills in pouches and lack limb girdles. Extant agnathans are the lampreys and the hagfishes. As the name implies, the skeletons of fishes of the class Chondrichthyes (from chondr, “cartilage,” and ichthyes, “fish”) are made entirely of cartilage. Modern fish of this class lack a swim bladder, and their scales and teeth are made up of the same placoid material. Sharks, skates, and rays are examples of cartilaginous fishes. The bony fishes are by far the largest class. Examples range from the tiny seahorse to the 450-kg (1,000-pound) blue marlin, from the flattened soles and flounders to the boxy puffers and ocean sunfishes. Unlike the scales of the cartilaginous fishes, those of bony fishes, when present, grow throughout life and are made up of thin overlapping plates of bone. Bony fishes also have an operculum that covers the gill slits.
The study of fishes, the science of ichthyology, is of broad importance. Fishes are of interest to humans for many reasons, the most important being their relationship with and dependence on the environment. A more obvious reason for interest in fishes is their role as a moderate but important part of the world’s food supply. This resource, once thought unlimited, is now realized to be finite and in delicate balance with the biological, chemical, and physical factors of the aquatic environment. Overfishing, pollution, and alteration of the environment are the chief enemies of proper fisheries management, both in fresh waters and in the ocean. (For a detailed discussion of the technology and economics of fisheries, see commercial fishing.) Another practical reason for studying fishes is their use in disease control. As predators on mosquito larvae, they help curb malaria and other mosquito-borne diseases.
Fishes are valuable laboratory animals in many aspects of medical and biological research. For example, the readiness of many fishes to acclimate to captivity has allowed biologists to study behaviour, physiology, and even ecology under relatively natural conditions. Fishes have been especially important in the study of animal behaviour, where research on fishes has provided a broad base for the understanding of the more flexible behaviour of the higher vertebrates. The zebra fish is used as a model in studies of gene expression.
There are aesthetic and recreational reasons for an interest in fishes. Millions of people keep live fishes in home aquariums for the simple pleasure of observing the beauty and behaviour of animals otherwise unfamiliar to them. Aquarium fishes provide a personal challenge to many aquarists, allowing them to test their ability to keep a small section of the natural environment in their homes. Sportfishing is another way of enjoying the natural environment, also indulged in by millions of people every year. Interest in aquarium fishes and sportfishing supports multimillion-dollar industries throughout the world.
Fishes have been in existence for more than 450 million years, during which time they have evolved repeatedly to fit into almost every conceivable type of aquatic habitat. In a sense, land vertebrates are simply highly modified fishes: when fishes colonized the land habitat, they became tetrapod (four-legged) land vertebrates. The popular conception of a fish as a slippery, streamlined aquatic animal that possesses fins and breathes by gills applies to many fishes, but far more fishes deviate from that conception than conform to it. For example, the body is elongate in many forms and greatly shortened in others; the body is flattened in some (principally in bottom-dwelling fishes) and laterally compressed in many others; the fins may be elaborately extended, forming intricate shapes, or they may be reduced or even lost; and the positions of the mouth, eyes, nostrils, and gill openings vary widely. Air breathers have appeared in several evolutionary lines.
Many fishes are cryptically coloured and shaped, closely matching their respective environments; others are among the most brilliantly coloured of all organisms, with a wide range of hues, often of striking intensity, on a single individual. The brilliance of pigments may be enhanced by the surface structure of the fish, so that it almost seems to glow. A number of unrelated fishes have actual light-producing organs. Many fishes are able to alter their coloration—some for the purpose of camouflage, others for the enhancement of behavioral signals.
Fishes range in adult length from less than 10 mm (0.4 inch) to more than 20 metres (60 feet) and in weight from about 1.5 grams (less than 0.06 ounce) to many thousands of kilograms. Some live in shallow thermal springs at temperatures slightly above 42 °C (100 °F), others in cold Arctic seas a few degrees below 0 °C (32 °F) or in cold deep waters more than 4,000 metres (13,100 feet) beneath the ocean surface. The structural and, especially, the physiological adaptations for life at such extremes are relatively poorly known and provide the scientifically curious with great incentive for study.
Almost all natural bodies of water bear fish life, the exceptions being very hot thermal ponds and extremely salt-alkaline lakes, such as the Dead Sea in Asia and the Great Salt Lake in North America. The present distribution of fishes is a result of the geological history and development of Earth as well as the ability of fishes to undergo evolutionary change and to adapt to the available habitats. Fishes may be seen to be distributed according to habitat and according to geographical area. Major habitat differences are marine and freshwater. For the most part, the fishes in a marine habitat differ from those in a freshwater habitat, even in adjacent areas, but some, such as the salmon, migrate from one to the other. The freshwater habitats may be seen to be of many kinds. Fishes found in mountain torrents, Arctic lakes, tropical lakes, temperate streams, and tropical rivers will all differ from each other, both in obvious gross structure and in physiological attributes. Even in closely adjacent habitats where, for example, a tropical mountain torrent enters a lowland stream, the fish fauna will differ. The marine habitats can be divided into deep ocean floors (benthic), mid-water oceanic (bathypelagic), surface oceanic (pelagic), rocky coast, sandy coast, muddy shores, bays, estuaries, and others. Also, for example, rocky coastal shores in tropical and temperate regions will have different fish faunas, even when such habitats occur along the same coastline.
Although much is known about the present geographical distribution of fishes, far less is known about how that distribution came about. Many parts of the fish fauna of the fresh waters of North America and Eurasia are related and undoubtedly have a common origin. The faunas of Africa and South America are related, extremely old, and probably an expression of the drifting apart of the two continents. The fauna of southern Asia is related to that of Central Asia, and some of it appears to have entered Africa. The extremely large shore-fish faunas of the Indian and tropical Pacific oceans comprise a related complex, but the tropical shore fauna of the Atlantic, although containing Indo-Pacific components, is relatively limited and probably younger. The Arctic and Antarctic marine faunas are quite different from each other. The shore fauna of the North Pacific is quite distinct, and that of the North Atlantic more limited and probably younger. Pelagic oceanic fishes, especially those in deep waters, are similar the world over, showing little geographical isolation in terms of family groups. The deep oceanic habitat is very much the same throughout the world, but species differences do exist, showing geographical areas determined by oceanic currents and water masses.
All aspects of the life of a fish are closely correlated with adaptation to the total environment, physical, chemical, and biological. In studies, all the interdependent aspects of fish, such as behaviour, locomotion, reproduction, and physical and physiological characteristics, must be taken into account.
Correlated with their adaptation to an extremely wide variety of habitats is the extremely wide variety of life cycles that fishes display. The great majority hatch from relatively small eggs a few days to several weeks or more after the eggs are scattered in the water. Newly hatched young are still partially undeveloped and are called larvae until body structures such as fins, skeleton, and some organs are fully formed. Larval life is often very short, usually less than a few weeks, but it can be very long, some lampreys continuing as larvae for at least five years. Young and larval fishes, before reaching sexual maturity, must grow considerably, and their small size and other factors often dictate that they live in a habitat different than that of the adults. For example, most tropical marine shore fishes have pelagic larvae. Larval food also is different, and larval fishes often live in shallow waters, where they may be less exposed to predators.
After a fish reaches adult size, the length of its life is subject to many factors, such as innate rates of aging, predation pressure, and the nature of the local climate. The longevity of a species in the protected environment of an aquarium may have nothing to do with how long members of that species live in the wild. Many small fishes live only one to three years at the most. In some species, however, individuals may live as long as 10 or 20 or even 100 years.
Fish behaviour is a complicated and varied subject. As in almost all animals with a central nervous system, the nature of a response of an individual fish to stimuli from its environment depends upon the inherited characteristics of its nervous system, on what it has learned from past experience, and on the nature of the stimuli. Compared with the variety of human responses, however, that of a fish is stereotyped, not subject to much modification by “thought” or learning, and investigators must guard against anthropomorphic interpretations of fish behaviour.
Fishes perceive the world around them by the usual senses of sight, smell, hearing, touch, and taste and by special lateral line water-current detectors. In the few fishes that generate electric fields, a process that might best be called electrolocation aids in perception. One or another of these senses often is emphasized at the expense of others, depending upon the fish’s other adaptations. In fishes with large eyes, the sense of smell may be reduced; others, with small eyes, hunt and feed primarily by smell (such as some eels).
Specialized behaviour is primarily concerned with the three most important activities in the fish’s life: feeding, reproduction, and escape from enemies. Schooling behaviour of sardines on the high seas, for instance, is largely a protective device to avoid enemies, but it is also associated with and modified by their breeding and feeding requirements. Predatory fishes are often solitary, lying in wait to dart suddenly after their prey, a kind of locomotion impossible for beaked parrot fishes, which feed on coral, swimming in small groups from one coral head to the next. In addition, some predatory fishes that inhabit pelagic environments, such as tunas, often school.
Sleep in fishes, all of which lack true eyelids, consists of a seemingly listless state in which the fish maintains its balance but moves slowly. If attacked or disturbed, most can dart away. A few kinds of fishes lie on the bottom to sleep. Most catfishes, some loaches, and some eels and electric fishes are strictly nocturnal, being active and hunting for food during the night and retiring during the day to holes, thick vegetation, or other protective parts of the environment.
Communication between members of a species or between members of two or more species often is extremely important, especially in breeding behaviour (see below Reproduction). The mode of communication may be visual, as between the small so-called cleaner fish and a large fish of a very different species. The larger fish often allows the cleaner to enter its mouth to remove gill parasites. The cleaner is recognized by its distinctive colour and actions and therefore is not eaten, even if the larger fish is normally a predator. Communication is often chemical, signals being sent by specific chemicals called pheromones.
Many fishes have a streamlined body and swim freely in open water. Fish locomotion is closely correlated with habitat and ecological niche (the general position of the animal to its environment).
Many fishes in both marine and fresh waters swim at the surface and have mouths adapted to feed best (and sometimes only) at the surface. Often such fishes are long and slender, able to dart at surface insects or at other surface fishes and in turn to dart away from predators; needlefishes, halfbeaks, and topminnows (such as killifish and mosquito fish) are good examples. Oceanic flying fishes escape their predators by gathering speed above the water surface, with the lower lobe of the tail providing thrust in the water. They then glide hundreds of yards on enlarged, winglike pectoral and pelvic fins. South American freshwater flying fishes escape their enemies by jumping and propelling their strongly keeled bodies out of the water.
So-called mid-water swimmers, the most common type of fish, are of many kinds and live in many habitats. The powerful fusiform tunas and the trouts, for example, are adapted for strong, fast swimming, the tunas to capture prey speedily in the open ocean and the trouts to cope with the swift currents of streams and rivers. The trout body form is well adapted to many habitats. Fishes that live in relatively quiet waters such as bays or lake shores or slow rivers usually are not strong, fast swimmers but are capable of short, quick bursts of speed to escape a predator. Many of these fishes have their sides flattened, examples being the sunfish and the freshwater angelfish of aquarists. Fish associated with the bottom or substrate usually are slow swimmers. Open-water plankton-feeding fishes almost always remain fusiform and are capable of rapid, strong movement (for example, sardines and herrings of the open ocean and also many small minnows of streams and lakes).
Bottom-living fishes are of many kinds and have undergone many types of modification of their body shape and swimming habits. Rays, which evolved from strong-swimming mid-water sharks, usually stay close to the bottom and move by undulating their large pectoral fins. Flounders live in a similar habitat and move over the bottom by undulating the entire body. Many bottom fishes dart from place to place, resting on the bottom between movements, a motion common in gobies. One goby relative, the mudskipper, has taken to living at the edge of pools along the shore of muddy mangrove swamps. It escapes its enemies by flipping rapidly over the mud, out of the water. Some catfishes, synbranchid eels, the so-called climbing perch, and a few other fishes venture out over damp ground to find more promising waters than those that they left. They move by wriggling their bodies, sometimes using strong pectoral fins; most have accessory air-breathing organs. Many bottom-dwelling fishes live in mud holes or rocky crevices. Marine eels and gobies commonly are found in such habitats and for the most part venture far beyond their cavelike homes. Some bottom dwellers, such as the clingfishes (Gobiesocidae), have developed powerful adhesive disks that enable them to remain in place on the substrate in areas such as rocky coasts, where the action of the waves is great.
The methods of reproduction in fishes are varied, but most fishes lay a large number of small eggs, fertilized and scattered outside of the body. The eggs of pelagic fishes usually remain suspended in the open water. Many shore and freshwater fishes lay eggs on the bottom or among plants. Some have adhesive eggs. The mortality of the young and especially of the eggs is very high, and often only a few individuals grow to maturity out of hundreds, thousands, and in some cases millions of eggs laid.
Males produce sperm, usually as a milky white substance called milt, in two (sometimes one) testes within the body cavity. In bony fishes a sperm duct leads from each testis to a urogenital opening behind the vent or anus. In sharks and rays and in cyclostomes the duct leads to a cloaca. Sometimes the pelvic fins are modified to help transmit the milt to the eggs at the female’s vent or on the substrate where the female has placed them. Sometimes accessory organs are used to fertilize females internally—for example, the claspers of many sharks and rays.
In the females the eggs are formed in two ovaries (sometimes only one) and pass through the ovaries to the urogenital opening and to the outside. In some fishes the eggs are fertilized internally but are shed before development takes place. Members of about a dozen families each of bony fishes (teleosts) and sharks bear live young. Many skates and rays also bear live young. In some bony fishes the eggs simply develop within the female, the young emerging when the eggs hatch (ovoviviparous). Others develop within the ovary and are nourished by ovarian tissues after hatching (viviparous). There are also other methods utilized by fishes to nourish young within the female. In all live-bearers the young are born at a relatively large size and are few in number. In one family of primarily marine fishes, the surfperches from the Pacific coast of North America, Japan, and Korea, the males of at least one species are born sexually mature, although they are not fully grown.
Some fishes are hermaphroditic—an individual producing both sperm and eggs, usually at different stages of its life. Self-fertilization, however, is probably rare.
Successful reproduction and, in many cases, defense of the eggs and the young are assured by rather stereotypical but often elaborate courtship and parental behaviour, either by the male or the female or both. Some fishes prepare nests by hollowing out depressions in the sand bottom (cichlids, for example), build nests with plant materials and sticky threads excreted by the kidneys (sticklebacks), or blow a cluster of mucus-covered bubbles at the water surface (gouramis). The eggs are laid in these structures. Some varieties of cichlids and catfishes incubate eggs in their mouths.
Some fishes, such as salmon, undergo long migrations from the ocean and up large rivers to spawn in the gravel beds where they themselves hatched (anadromous fishes). Some, such as the freshwater eels (family Anguillidae), live and grow to maturity in fresh water and migrate to the sea to spawn (catadromous fishes). Other fishes undertake shorter migrations from lakes into streams, within the ocean, or enter spawning habitats that they do not ordinarily occupy in other ways.
The basic structure and function of the fish body are similar to those of all other vertebrates. The usual four types of tissues are present: surface or epithelial, connective (bone, cartilage, and fibrous tissues, as well as their derivative, blood), nerve, and muscle tissues. In addition, the fish’s organs and organ systems parallel those of other vertebrates.
The typical fish body is streamlined and spindle-shaped, with an anterior head, a gill apparatus, and a heart, the latter lying in the midline just below the gill chamber. The body cavity, containing the vital organs, is situated behind the head in the lower anterior part of the body. The anus usually marks the posterior termination of the body cavity and most often occurs just in front of the base of the anal fin. The spinal cord and vertebral column continue from the posterior part of the head to the base of the tail fin, passing dorsal to the body cavity and through the caudal (tail) region behind the body cavity. Most of the body is of muscular tissue, a high proportion of which is necessitated by swimming. In the course of evolution this basic body plan has been modified repeatedly into the many varieties of fish shapes that exist today.
The skeleton forms an integral part of the fish’s locomotion system, as well as serving to protect vital parts. The internal skeleton consists of the skull bones (except for the roofing bones of the head, which are really part of the external skeleton), the vertebral column, and the fin supports (fin rays). The fin supports are derived from the external skeleton but will be treated here because of their close functional relationship to the internal skeleton. The internal skeleton of cyclostomes, sharks, and rays is of cartilage; that of many fossil groups and some primitive living fishes is mostly of cartilage but may include some bone. In place of the vertebral column, the earliest vertebrates had a fully developed notochord, a flexible stiff rod of viscous cells surrounded by a strong fibrous sheath. During the evolution of modern fishes the rod was replaced in part by cartilage and then by ossified cartilage. Sharks and rays retain a cartilaginous vertebral column; bony fishes have spool-shaped vertebrae that in the more primitive living forms only partially replace the notochord. The skull, including the gill arches and jaws of bony fishes, is fully, or at least partially, ossified. That of sharks and rays remains cartilaginous, at times partially replaced by calcium deposits but never by true bone.
The supportive elements of the fins (basal or radial bones or both) have changed greatly during fish evolution. Some of these changes are described in the section below (Evolution and paleontology). Most fishes possess a single dorsal fin on the midline of the back. Many have two and a few have three dorsal fins. The other fins are the single tail and anal fins and paired pelvic and pectoral fins. A small fin, the adipose fin, with hairlike fin rays, occurs in many of the relatively primitive teleosts (such as trout) on the back near the base of the caudal fin.
The skin of a fish must serve many functions. It aids in maintaining the osmotic balance, provides physical protection for the body, is the site of coloration, contains sensory receptors, and, in some fishes, functions in respiration. Mucous glands, which aid in maintaining the water balance and offer protection from bacteria, are extremely numerous in fish skin, especially in cyclostomes and teleosts. Since mucous glands are present in the modern lampreys, it is reasonable to assume that they were present in primitive fishes, such as the ancient Silurian and Devonian agnathans. Protection from abrasion and predation is another function of the fish skin, and dermal (skin) bone arose early in fish evolution in response to this need. It is thought that bone first evolved in skin and only later invaded the cartilaginous areas of the fish’s body, to provide additional support and protection. There is some argument as to which came first, cartilage or bone, and fossil evidence does not settle the question. In any event, dermal bone has played an important part in fish evolution and has different characteristics in different groups of fishes. Several groups are characterized at least in part by the kind of bony scales they possess.
Scales have played an important part in the evolution of fishes. Primitive fishes usually had thick bony plates or thick scales in several layers of bone, enamel, and related substances. Modern teleost fishes have scales of bone, which, while still protective, allow much more freedom of motion in the body. A few modern teleosts (some catfishes, sticklebacks, and others) have secondarily acquired bony plates in the skin. Modern and early sharks possessed placoid scales, a relatively primitive type of scale with a toothlike structure, consisting of an outside layer of enamel-like substance (vitrodentine), an inner layer of dentine, and a pulp cavity containing nerves and blood vessels. Primitive bony fishes had thick scales of either the ganoid or the cosmoid type. Cosmoid scales have a hard, enamel-like outer layer, an inner layer of cosmine (a form of dentine), and then a layer of vascular bone (isopedine). In ganoid scales the hard outer layer is different chemically and is called ganoin. Under this is a cosminelike layer and then a vascular bony layer. The thin, translucent bony scales of modern fishes, called cycloid and ctenoid (the latter distinguished by serrations at the edges), lack enameloid and dentine layers.
Skin has several other functions in fishes. It is well supplied with nerve endings and presumably receives tactile, thermal, and pain stimuli. Skin is also well supplied with blood vessels. Some fishes breathe in part through the skin, by the exchange of oxygen and carbon dioxide between the surrounding water and numerous small blood vessels near the skin surface.
Skin serves as protection through the control of coloration. Fishes exhibit an almost limitless range of colours. The colours often blend closely with the surroundings, effectively hiding the animal. Many fishes use bright colours for territorial advertisement or as recognition marks for other members of their own species, or sometimes for members of other species. Many fishes can change their colour to a greater or lesser degree, by movement of pigment within the pigment cells (chromatophores). Black pigment cells (melanophores), of almost universal occurrence in fishes, are often juxtaposed with other pigment cells. When placed beneath iridocytes or leucophores (bearing the silvery or white pigment guanine), melanophores produce structural colours of blue and green. These colours are often extremely intense, because they are formed by refraction of light through the needlelike crystals of guanine. The blue and green refracted colours are often relatively pure, lacking the red and yellow rays, which have been absorbed by the black pigment (melanin) of the melanophores. Yellow, orange, and red colours are produced by erythrophores, cells containing the appropriate carotenoid pigments. Other colours are produced by combinations of melanophores, erythrophores, and iridocytes.
The major portion of the body of most fishes consists of muscles. Most of the mass is trunk musculature, the fin muscles usually being relatively small. The caudal fin is usually the most powerful fin, being moved by the trunk musculature. The body musculature is usually arranged in rows of chevron-shaped segments on each side. Contractions of these segments, each attached to adjacent vertebrae and vertebral processes, bends the body on the vertebral joint, producing successive undulations of the body, passing from the head to the tail, and producing driving strokes of the tail. It is the latter that provides the strong forward movement for most fishes.
The digestive system, in a functional sense, starts at the mouth, with the teeth used to capture prey or collect plant foods. Mouth shape and tooth structure vary greatly in fishes, depending on the kind of food normally eaten. Most fishes are predacious, feeding on small invertebrates or other fishes and have simple conical teeth on the jaws, on at least some of the bones of the roof of the mouth, and on special gill arch structures just in front of the esophagus. The latter are throat teeth. Most predacious fishes swallow their prey whole, and the teeth are used for grasping and holding prey, for orienting prey to be swallowed (head first) and for working the prey toward the esophagus. There are a variety of tooth types in fishes. Some fishes, such as sharks and piranhas, have cutting teeth for biting chunks out of their victims. A shark’s tooth, although superficially like that of a piranha, appears in many respects to be a modified scale, while that of the piranha is like that of other bony fishes, consisting of dentine and enamel. Parrot fishes have beaklike mouths with short incisor-like teeth for breaking off coral and have heavy pavementlike throat teeth for crushing the coral. Some catfishes have small brushlike teeth, arranged in rows on the jaws, for scraping plant and animal growth from rocks. Many fishes (such as the Cyprinidae or minnows) have no jaw teeth at all but have very strong throat teeth.
Some fishes gather planktonic food by straining it from their gill cavities with numerous elongate stiff rods (gill rakers) anchored by one end to the gill bars. The food collected on these rods is passed to the throat, where it is swallowed. Most fishes have only short gill rakers that help keep food particles from escaping out the mouth cavity into the gill chamber.
Once reaching the throat, food enters a short, often greatly distensible esophagus, a simple tube with a muscular wall leading into a stomach. The stomach varies greatly in fishes, depending upon the diet. In most predacious fishes it is a simple straight or curved tube or pouch with a muscular wall and a glandular lining. Food is largely digested there and leaves the stomach in liquid form.
Between the stomach and the intestine, ducts enter the digestive tube from the liver and pancreas. The liver is a large, clearly defined organ. The pancreas may be embedded in it, diffused through it, or broken into small parts spread along some of the intestine. The junction between the stomach and the intestine is marked by a muscular valve. Pyloric ceca (blind sacs) occur in some fishes at this junction and have a digestive or absorptive function or both.
The intestine itself is quite variable in length, depending upon the fish’s diet. It is short in predacious forms, sometimes no longer than the body cavity, but long in herbivorous forms, being coiled and several times longer than the entire length of the fish in some species of South American catfishes. The intestine is primarily an organ for absorbing nutrients into the bloodstream. The larger its internal surface, the greater its absorptive efficiency, and a spiral valve is one method of increasing its absorption surface.
Sharks, rays, chimaeras, lungfishes, surviving chondrosteans, holosteans, and even a few of the more primitive teleosts have a spiral valve or at least traces of it in the intestine. Most modern teleosts have increased the area of the intestinal walls by having numerous folds and villi (fingerlike projections) somewhat like those in humans. Undigested substances are passed to the exterior through the anus in most teleost fishes. In lungfishes, sharks, and rays, it is first passed through the cloaca, a common cavity receiving the intestinal opening and the ducts from the urogenital system.
Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills. The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour. Water taken in continuously through the mouth passes backward between the gill bars and over the gill filaments, where the exchange of gases takes place. The gills are protected by a gill cover in teleosts and many other fishes but by flaps of skin in sharks, rays, and some of the older fossil fish groups. The blood capillaries in the gill filaments are close to the gill surface to take up oxygen from the water and to give up excess carbon dioxide to the water.
Most modern fishes have a hydrostatic (ballast) organ, called the swim bladder, that lies in the body cavity just below the kidney and above the stomach and intestine. It originated as a diverticulum of the digestive canal. In advanced teleosts, especially the acanthopterygians, the bladder has lost its connection with the digestive tract, a condition called physoclistic. The connection has been retained (physostomous) by many relatively primitive teleosts. In several unrelated lines of fishes, the bladder has become specialized as a lung or, at least, as a highly vascularized accessory breathing organ. Some fishes with such accessory organs are obligate air breathers and will drown if denied access to the surface, even in well-oxygenated water. Fishes with a hydrostatic form of swim bladder can control their depth by regulating the amount of gas in the bladder. The gas, mostly oxygen, is secreted into the bladder by special glands, rendering the fish more buoyant; the gas is absorbed into the bloodstream by another special organ, reducing the overall buoyancy and allowing the fish to sink. Some deep-sea fishes may have oils, rather than gas, in the bladder. Other deep-sea and some bottom-living forms have much-reduced swim bladders or have lost the organ entirely.
The swim bladder of fishes follows the same developmental pattern as the lungs of land vertebrates. There is no doubt that the two structures have the same historical origin in primitive fishes. More or less intermediate forms still survive among the more primitive types of fishes, such as the lungfishes Lepidosiren and Protopterus.
The circulatory, or blood vascular, system consists of the heart, the arteries, the capillaries, and the veins. It is in the capillaries that the interchange of oxygen, carbon dioxide, nutrients, and other substances such as hormones and waste products takes place. The capillaries lead to the veins, which return the venous blood with its waste products to the heart, kidneys, and gills. There are two kinds of capillary beds: those in the gills and those in the rest of the body. The heart, a folded continuous muscular tube with three or four saclike enlargements, undergoes rhythmic contractions and receives venous blood in a sinus venosus. It passes the blood to an auricle and then into a thick muscular pump, the ventricle. From the ventricle the blood goes to a bulbous structure at the base of a ventral aorta just below the gills. The blood passes to the afferent (receiving) arteries of the gill arches and then to the gill capillaries. There waste gases are given off to the environment, and oxygen is absorbed. The oxygenated blood enters efferent (exuant) arteries of the gill arches and then flows into the dorsal aorta. From there blood is distributed to the tissues and organs of the body. One-way valves prevent backflow. The circulation of fishes thus differs from that of the reptiles, birds, and mammals in that oxygenated blood is not returned to the heart prior to distribution to the other parts of the body.
The primary excretory organ in fishes, as in other vertebrates, is the kidney. In fishes some excretion also takes place in the digestive tract, skin, and especially the gills (where ammonia is given off). Compared with land vertebrates, fishes have a special problem in maintaining their internal environment at a constant concentration of water and dissolved substances, such as salts. Proper balance of the internal environment (homeostasis) of a fish is in a great part maintained by the excretory system, especially the kidney.
The kidney, gills, and skin play an important role in maintaining a fish’s internal environment and checking the effects of osmosis. Marine fishes live in an environment in which the water around them has a greater concentration of salts than they can have inside their body and still maintain life. Freshwater fishes, on the other hand, live in water with a much lower concentration of salts than they require inside their bodies. Osmosis tends to promote the loss of water from the body of a marine fish and absorption of water by that of a freshwater fish. Mucus in the skin tends to slow the process but is not a sufficient barrier to prevent the movement of fluids through the permeable skin. When solutions on two sides of a permeable membrane have different concentrations of dissolved substances, water will pass through the membrane into the more concentrated solution, while the dissolved chemicals move into the area of lower concentration (diffusion).
The kidney of freshwater fishes is often larger in relation to body weight than that of marine fishes. In both groups the kidney excretes wastes from the body, but the kidney of freshwater fishes also excretes large amounts of water, counteracting the water absorbed through the skin. Freshwater fishes tend to lose salt to the environment and must replace it. They get some salt from their food, but the gills and skin inside the mouth actively absorb salt from water passed through the mouth. This absorption is performed by special cells capable of moving salts against the diffusion gradient. Freshwater fishes drink very little water and take in little water with their food.
Marine fishes must conserve water, and therefore their kidneys excrete little water. To maintain their water balance, marine fishes drink large quantities of seawater, retaining most of the water and excreting the salt. Most nitrogenous waste in marine fishes appears to be secreted by the gills as ammonia. Marine fishes can excrete salt by clusters of special cells (chloride cells) in the gills.
There are several teleosts—for example, the salmon—that travel between fresh water and seawater and must adjust to the reversal of osmotic gradients. They adjust their physiological processes by spending time (often surprisingly little time) in the intermediate brackish environment.
Marine hagfishes, sharks, and rays have osmotic concentrations in their blood about equal to that of seawater and so do not have to drink water nor perform much physiological work to maintain their osmotic balance. In sharks and rays the osmotic concentration is kept high by retention of urea in the blood. Freshwater sharks have a lowered concentration of urea in the blood.
Endocrine glands secrete their products into the bloodstream and body tissues and, along with the central nervous system, control and regulate many kinds of body functions. Cyclostomes have a well-developed endocrine system, and presumably it was well developed in the early Agnatha, ancestral to modern fishes. Although the endocrine system in fishes is similar to that of higher vertebrates, there are numerous differences in detail. The pituitary, the thyroid, the suprarenals, the adrenals, the pancreatic islets, the sex glands (ovaries and testes), the inner wall of the intestine, and the bodies of the ultimobranchial gland make up the endocrine system in fishes. There are some others whose function is not well understood. These organs regulate sexual activity and reproduction, growth, osmotic pressure, general metabolic activities such as the storage of fat and the utilization of foodstuffs, blood pressure, and certain aspects of skin colour. Many of these activities are also controlled in part by the central nervous system, which works with the endocrine system in maintaining the life of a fish. Some parts of the endocrine system are developmentally, and undoubtedly evolutionarily, derived from the nervous system.
As in all vertebrates, the nervous system of fishes is the primary mechanism coordinating body activities, as well as integrating these activities in the appropriate manner with stimuli from the environment. The central nervous system, consisting of the brain and spinal cord, is the primary integrating mechanism. The peripheral nervous system, consisting of nerves that connect the brain and spinal cord to various body organs, carries sensory information from special receptor organs such as the eyes, internal ears, nares (sense of smell), taste glands, and others to the integrating centres of the brain and spinal cord. The peripheral nervous system also carries information via different nerve cells from the integrating centres of the brain and spinal cord. This coded information is carried to the various organs and body systems, such as the skeletal muscular system, for appropriate action in response to the original external or internal stimulus. Another branch of the nervous system, the autonomic nervous system, helps to coordinate the activities of many glands and organs and is itself closely connected to the integrating centres of the brain.
The brain of the fish is divided into several anatomical and functional parts, all closely interconnected but each serving as the primary centre of integrating particular kinds of responses and activities. Several of these centres or parts are primarily associated with one type of sensory perception, such as sight, hearing, or smell (olfaction).
The sense of smell is important in almost all fishes. Certain eels with tiny eyes depend mostly on smell for location of food. The olfactory, or nasal, organ of fishes is located on the dorsal surface of the snout. The lining of the nasal organ has special sensory cells that perceive chemicals dissolved in the water, such as substances from food material, and send sensory information to the brain by way of the first cranial nerve. Odour also serves as an alarm system. Many fishes, especially various species of freshwater minnows, react with alarm to a chemical released from the skin of an injured member of their own species.
Many fishes have a well-developed sense of taste, and tiny pitlike taste buds or organs are located not only within their mouth cavities but also over their heads and parts of their body. Catfishes, which often have poor vision, have barbels (“whiskers”) that serve as supplementary taste organs, those around the mouth being actively used to search out food on the bottom. Some species of naturally blind cave fishes are especially well supplied with taste buds, which often cover most of their body surface.
Sight is extremely important in most fishes. The eye of a fish is basically like that of all other vertebrates, but the eyes of fishes are extremely varied in structure and adaptation. In general, fishes living in dark and dim water habitats have large eyes, unless they have specialized in some compensatory way so that another sense (such as smell) is dominant, in which case the eyes will often be reduced. Fishes living in brightly lighted shallow waters often will have relatively small but efficient eyes. Cyclostomes have somewhat less elaborate eyes than other fishes, with skin stretched over the eyeball perhaps making their vision somewhat less effective. Most fishes have a spherical lens and accommodate their vision to far or near subjects by moving the lens within the eyeball. A few sharks accommodate by changing the shape of the lens, as in land vertebrates. Those fishes that are heavily dependent upon the eyes have especially strong muscles for accommodation. Most fishes see well, despite the restrictions imposed by frequent turbidity of the water and by light refraction.
Fossil evidence suggests that colour vision evolved in fishes more than 300 million years ago, but not all living fishes have retained this ability. Experimental evidence indicates that many shallow-water fishes, if not all, have colour vision and see some colours especially well, but some bottom-dwelling shore fishes live in areas where the water is sufficiently deep to filter out most if not all colours, and these fishes apparently never see colours. When tested in shallow water, they apparently are unable to respond to colour differences.
Sound perception and balance are intimately associated senses in a fish. The organs of hearing are entirely internal, located within the skull, on each side of the brain and somewhat behind the eyes. Sound waves, especially those of low frequencies, travel readily through water and impinge directly upon the bones and fluids of the head and body, to be transmitted to the hearing organs. Fishes readily respond to sound; for example, a trout conditioned to escape by the approach of fishermen will take flight upon perceiving footsteps on a stream bank even if it cannot see a fisherman. Compared with humans, however, the range of sound frequencies heard by fishes is greatly restricted. Many fishes communicate with each other by producing sounds in their swim bladders, in their throats by rasping their teeth, and in other ways.
A fish or other vertebrate seldom has to rely on a single type of sensory information to determine the nature of the environment around it. A catfish uses taste and touch when examining a food object with its oral barbels. Like most other animals, fishes have many touch receptors over their body surface. Pain and temperature receptors also are present in fishes and presumably produce the same kind of information to a fish as to humans. Fishes react in a negative fashion to stimuli that would be painful to human beings, suggesting that they feel a sensation of pain.
An important sensory system in fishes that is absent in other vertebrates (except some amphibians) is the lateral line system. This consists of a series of heavily innervated small canals located in the skin and bone around the eyes, along the lower jaw, over the head, and down the mid-side of the body, where it is associated with the scales. Intermittently along these canals are located tiny sensory organs (pit organs) that apparently detect changes in pressure. The system allows a fish to sense changes in water currents and pressure, thereby helping the fish to orient itself to the various changes that occur in the physical environment.
Fish, any of approximately 34,000 species of vertebrate animals (phylum Chordata) found in the fresh and salt waters of the world. Living species range from the primitive jawless lampreys and hagfishes through the cartilaginous sharks, skates, and rays to the abundant and diverse bony fishes. Most fish species are cold-blooded; however, one species, the opah (Lampris guttatus), is warm-blooded.
The term fish is applied to a variety of vertebrates of several evolutionary lines. It describes a life-form rather than a taxonomic group. As members of the phylum Chordata, fish share certain features with other vertebrates. These features are gill slits at some point in the life cycle, a notochord, or skeletal supporting rod, a dorsal hollow nerve cord, and a tail. Living fishes represent some five classes, which are as distinct from one another as are the four classes of familiar air-breathing animals—amphibians, reptiles, birds, and mammals. For example, the jawless fishes (Agnatha) have gills in pouches and lack limb girdles. Extant agnathans are the lampreys and the hagfishes. As the name implies, the skeletons of fishes of the class Chondrichthyes (from chondr, “cartilage,” and ichthyes, “fish”) are made entirely of cartilage. Modern fish of this class lack a swim bladder, and their scales and teeth are made up of the same placoid material. Sharks, skates, and rays are examples of cartilaginous fishes. The bony fishes are by far the largest class. Examples range from the tiny seahorse to the 450-kg (1,000-pound) blue marlin, from the flattened soles and flounders to the boxy puffers and ocean sunfishes. Unlike the scales of the cartilaginous fishes, those of bony fishes, when present, grow throughout life and are made up of thin overlapping plates of bone. Bony fishes also have an operculum that covers the gill slits.
The study of fishes, the science of ichthyology, is of broad importance. Fishes are of interest to humans for many reasons, the most important being their relationship with and dependence on the environment. A more obvious reason for interest in fishes is their role as a moderate but important part of the world’s food supply. This resource, once thought unlimited, is now realized to be finite and in delicate balance with the biological, chemical, and physical factors of the aquatic environment. Overfishing, pollution, and alteration of the environment are the chief enemies of proper fisheries management, both in fresh waters and in the ocean. (For a detailed discussion of the technology and economics of fisheries, see commercial fishing.) Another practical reason for studying fishes is their use in disease control. As predators on mosquito larvae, they help curb malaria and other mosquito-borne diseases.
Fishes are valuable laboratory animals in many aspects of medical and biological research. For example, the readiness of many fishes to acclimate to captivity has allowed biologists to study behaviour, physiology, and even ecology under relatively natural conditions. Fishes have been especially important in the study of animal behaviour, where research on fishes has provided a broad base for the understanding of the more flexible behaviour of the higher vertebrates. The zebra fish is used as a model in studies of gene expression.
There are aesthetic and recreational reasons for an interest in fishes. Millions of people keep live fishes in home aquariums for the simple pleasure of observing the beauty and behaviour of animals otherwise unfamiliar to them. Aquarium fishes provide a personal challenge to many aquarists, allowing them to test their ability to keep a small section of the natural environment in their homes. Sportfishing is another way of enjoying the natural environment, also indulged in by millions of people every year. Interest in aquarium fishes and sportfishing supports multimillion-dollar industries throughout the world.
Fishes have been in existence for more than 450 million years, during which time they have evolved repeatedly to fit into almost every conceivable type of aquatic habitat. In a sense, land vertebrates are simply highly modified fishes: when fishes colonized the land habitat, they became tetrapod (four-legged) land vertebrates. The popular conception of a fish as a slippery, streamlined aquatic animal that possesses fins and breathes by gills applies to many fishes, but far more fishes deviate from that conception than conform to it. For example, the body is elongate in many forms and greatly shortened in others; the body is flattened in some (principally in bottom-dwelling fishes) and laterally compressed in many others; the fins may be elaborately extended, forming intricate shapes, or they may be reduced or even lost; and the positions of the mouth, eyes, nostrils, and gill openings vary widely. Air breathers have appeared in several evolutionary lines.
Many fishes are cryptically coloured and shaped, closely matching their respective environments; others are among the most brilliantly coloured of all organisms, with a wide range of hues, often of striking intensity, on a single individual. The brilliance of pigments may be enhanced by the surface structure of the fish, so that it almost seems to glow. A number of unrelated fishes have actual light-producing organs. Many fishes are able to alter their coloration—some for the purpose of camouflage, others for the enhancement of behavioral signals.
Fishes range in adult length from less than 10 mm (0.4 inch) to more than 20 metres (60 feet) and in weight from about 1.5 grams (less than 0.06 ounce) to many thousands of kilograms. Some live in shallow thermal springs at temperatures slightly above 42 °C (100 °F), others in cold Arctic seas a few degrees below 0 °C (32 °F) or in cold deep waters more than 4,000 metres (13,100 feet) beneath the ocean surface. The structural and, especially, the physiological adaptations for life at such extremes are relatively poorly known and provide the scientifically curious with great incentive for study.
Almost all natural bodies of water bear fish life, the exceptions being very hot thermal ponds and extremely salt-alkaline lakes, such as the Dead Sea in Asia and the Great Salt Lake in North America. The present distribution of fishes is a result of the geological history and development of Earth as well as the ability of fishes to undergo evolutionary change and to adapt to the available habitats. Fishes may be seen to be distributed according to habitat and according to geographical area. Major habitat differences are marine and freshwater. For the most part, the fishes in a marine habitat differ from those in a freshwater habitat, even in adjacent areas, but some, such as the salmon, migrate from one to the other. The freshwater habitats may be seen to be of many kinds. Fishes found in mountain torrents, Arctic lakes, tropical lakes, temperate streams, and tropical rivers will all differ from each other, both in obvious gross structure and in physiological attributes. Even in closely adjacent habitats where, for example, a tropical mountain torrent enters a lowland stream, the fish fauna will differ. The marine habitats can be divided into deep ocean floors (benthic), mid-water oceanic (bathypelagic), surface oceanic (pelagic), rocky coast, sandy coast, muddy shores, bays, estuaries, and others. Also, for example, rocky coastal shores in tropical and temperate regions will have different fish faunas, even when such habitats occur along the same coastline.
Although much is known about the present geographical distribution of fishes, far less is known about how that distribution came about. Many parts of the fish fauna of the fresh waters of North America and Eurasia are related and undoubtedly have a common origin. The faunas of Africa and South America are related, extremely old, and probably an expression of the drifting apart of the two continents. The fauna of southern Asia is related to that of Central Asia, and some of it appears to have entered Africa. The extremely large shore-fish faunas of the Indian and tropical Pacific oceans comprise a related complex, but the tropical shore fauna of the Atlantic, although containing Indo-Pacific components, is relatively limited and probably younger. The Arctic and Antarctic marine faunas are quite different from each other. The shore fauna of the North Pacific is quite distinct, and that of the North Atlantic more limited and probably younger. Pelagic oceanic fishes, especially those in deep waters, are similar the world over, showing little geographical isolation in terms of family groups. The deep oceanic habitat is very much the same throughout the world, but species differences do exist, showing geographical areas determined by oceanic currents and water masses.
All aspects of the life of a fish are closely correlated with adaptation to the total environment, physical, chemical, and biological. In studies, all the interdependent aspects of fish, such as behaviour, locomotion, reproduction, and physical and physiological characteristics, must be taken into account.
Correlated with their adaptation to an extremely wide variety of habitats is the extremely wide variety of life cycles that fishes display. The great majority hatch from relatively small eggs a few days to several weeks or more after the eggs are scattered in the water. Newly hatched young are still partially undeveloped and are called larvae until body structures such as fins, skeleton, and some organs are fully formed. Larval life is often very short, usually less than a few weeks, but it can be very long, some lampreys continuing as larvae for at least five years. Young and larval fishes, before reaching sexual maturity, must grow considerably, and their small size and other factors often dictate that they live in a habitat different than that of the adults. For example, most tropical marine shore fishes have pelagic larvae. Larval food also is different, and larval fishes often live in shallow waters, where they may be less exposed to predators.
After a fish reaches adult size, the length of its life is subject to many factors, such as innate rates of aging, predation pressure, and the nature of the local climate. The longevity of a species in the protected environment of an aquarium may have nothing to do with how long members of that species live in the wild. Many small fishes live only one to three years at the most. In some species, however, individuals may live as long as 10 or 20 or even 100 years.
Fish behaviour is a complicated and varied subject. As in almost all animals with a central nervous system, the nature of a response of an individual fish to stimuli from its environment depends upon the inherited characteristics of its nervous system, on what it has learned from past experience, and on the nature of the stimuli. Compared with the variety of human responses, however, that of a fish is stereotyped, not subject to much modification by “thought” or learning, and investigators must guard against anthropomorphic interpretations of fish behaviour.
Fishes perceive the world around them by the usual senses of sight, smell, hearing, touch, and taste and by special lateral line water-current detectors. In the few fishes that generate electric fields, a process that might best be called electrolocation aids in perception. One or another of these senses often is emphasized at the expense of others, depending upon the fish’s other adaptations. In fishes with large eyes, the sense of smell may be reduced; others, with small eyes, hunt and feed primarily by smell (such as some eels).
Specialized behaviour is primarily concerned with the three most important activities in the fish’s life: feeding, reproduction, and escape from enemies. Schooling behaviour of sardines on the high seas, for instance, is largely a protective device to avoid enemies, but it is also associated with and modified by their breeding and feeding requirements. Predatory fishes are often solitary, lying in wait to dart suddenly after their prey, a kind of locomotion impossible for beaked parrot fishes, which feed on coral, swimming in small groups from one coral head to the next. In addition, some predatory fishes that inhabit pelagic environments, such as tunas, often school.
Sleep in fishes, all of which lack true eyelids, consists of a seemingly listless state in which the fish maintains its balance but moves slowly. If attacked or disturbed, most can dart away. A few kinds of fishes lie on the bottom to sleep. Most catfishes, some loaches, and some eels and electric fishes are strictly nocturnal, being active and hunting for food during the night and retiring during the day to holes, thick vegetation, or other protective parts of the environment.
Communication between members of a species or between members of two or more species often is extremely important, especially in breeding behaviour (see below Reproduction). The mode of communication may be visual, as between the small so-called cleaner fish and a large fish of a very different species. The larger fish often allows the cleaner to enter its mouth to remove gill parasites. The cleaner is recognized by its distinctive colour and actions and therefore is not eaten, even if the larger fish is normally a predator. Communication is often chemical, signals being sent by specific chemicals called pheromones.
Many fishes have a streamlined body and swim freely in open water. Fish locomotion is closely correlated with habitat and ecological niche (the general position of the animal to its environment).
Many fishes in both marine and fresh waters swim at the surface and have mouths adapted to feed best (and sometimes only) at the surface. Often such fishes are long and slender, able to dart at surface insects or at other surface fishes and in turn to dart away from predators; needlefishes, halfbeaks, and topminnows (such as killifish and mosquito fish) are good examples. Oceanic flying fishes escape their predators by gathering speed above the water surface, with the lower lobe of the tail providing thrust in the water. They then glide hundreds of yards on enlarged, winglike pectoral and pelvic fins. South American freshwater flying fishes escape their enemies by jumping and propelling their strongly keeled bodies out of the water.
So-called mid-water swimmers, the most common type of fish, are of many kinds and live in many habitats. The powerful fusiform tunas and the trouts, for example, are adapted for strong, fast swimming, the tunas to capture prey speedily in the open ocean and the trouts to cope with the swift currents of streams and rivers. The trout body form is well adapted to many habitats. Fishes that live in relatively quiet waters such as bays or lake shores or slow rivers usually are not strong, fast swimmers but are capable of short, quick bursts of speed to escape a predator. Many of these fishes have their sides flattened, examples being the sunfish and the freshwater angelfish of aquarists. Fish associated with the bottom or substrate usually are slow swimmers. Open-water plankton-feeding fishes almost always remain fusiform and are capable of rapid, strong movement (for example, sardines and herrings of the open ocean and also many small minnows of streams and lakes).
Bottom-living fishes are of many kinds and have undergone many types of modification of their body shape and swimming habits. Rays, which evolved from strong-swimming mid-water sharks, usually stay close to the bottom and move by undulating their large pectoral fins. Flounders live in a similar habitat and move over the bottom by undulating the entire body. Many bottom fishes dart from place to place, resting on the bottom between movements, a motion common in gobies. One goby relative, the mudskipper, has taken to living at the edge of pools along the shore of muddy mangrove swamps. It escapes its enemies by flipping rapidly over the mud, out of the water. Some catfishes, synbranchid eels, the so-called climbing perch, and a few other fishes venture out over damp ground to find more promising waters than those that they left. They move by wriggling their bodies, sometimes using strong pectoral fins; most have accessory air-breathing organs. Many bottom-dwelling fishes live in mud holes or rocky crevices. Marine eels and gobies commonly are found in such habitats and for the most part venture far beyond their cavelike homes. Some bottom dwellers, such as the clingfishes (Gobiesocidae), have developed powerful adhesive disks that enable them to remain in place on the substrate in areas such as rocky coasts, where the action of the waves is great.
The methods of reproduction in fishes are varied, but most fishes lay a large number of small eggs, fertilized and scattered outside of the body. The eggs of pelagic fishes usually remain suspended in the open water. Many shore and freshwater fishes lay eggs on the bottom or among plants. Some have adhesive eggs. The mortality of the young and especially of the eggs is very high, and often only a few individuals grow to maturity out of hundreds, thousands, and in some cases millions of eggs laid.
Males produce sperm, usually as a milky white substance called milt, in two (sometimes one) testes within the body cavity. In bony fishes a sperm duct leads from each testis to a urogenital opening behind the vent or anus. In sharks and rays and in cyclostomes the duct leads to a cloaca. Sometimes the pelvic fins are modified to help transmit the milt to the eggs at the female’s vent or on the substrate where the female has placed them. Sometimes accessory organs are used to fertilize females internally—for example, the claspers of many sharks and rays.
In the females the eggs are formed in two ovaries (sometimes only one) and pass through the ovaries to the urogenital opening and to the outside. In some fishes the eggs are fertilized internally but are shed before development takes place. Members of about a dozen families each of bony fishes (teleosts) and sharks bear live young. Many skates and rays also bear live young. In some bony fishes the eggs simply develop within the female, the young emerging when the eggs hatch (ovoviviparous). Others develop within the ovary and are nourished by ovarian tissues after hatching (viviparous). There are also other methods utilized by fishes to nourish young within the female. In all live-bearers the young are born at a relatively large size and are few in number. In one family of primarily marine fishes, the surfperches from the Pacific coast of North America, Japan, and Korea, the males of at least one species are born sexually mature, although they are not fully grown.
Some fishes are hermaphroditic—an individual producing both sperm and eggs, usually at different stages of its life. Self-fertilization, however, is probably rare.
Successful reproduction and, in many cases, defense of the eggs and the young are assured by rather stereotypical but often elaborate courtship and parental behaviour, either by the male or the female or both. Some fishes prepare nests by hollowing out depressions in the sand bottom (cichlids, for example), build nests with plant materials and sticky threads excreted by the kidneys (sticklebacks), or blow a cluster of mucus-covered bubbles at the water surface (gouramis). The eggs are laid in these structures. Some varieties of cichlids and catfishes incubate eggs in their mouths.
Some fishes, such as salmon, undergo long migrations from the ocean and up large rivers to spawn in the gravel beds where they themselves hatched (anadromous fishes). Some, such as the freshwater eels (family Anguillidae), live and grow to maturity in fresh water and migrate to the sea to spawn (catadromous fishes). Other fishes undertake shorter migrations from lakes into streams, within the ocean, or enter spawning habitats that they do not ordinarily occupy in other ways.
The basic structure and function of the fish body are similar to those of all other vertebrates. The usual four types of tissues are present: surface or epithelial, connective (bone, cartilage, and fibrous tissues, as well as their derivative, blood), nerve, and muscle tissues. In addition, the fish’s organs and organ systems parallel those of other vertebrates.
The typical fish body is streamlined and spindle-shaped, with an anterior head, a gill apparatus, and a heart, the latter lying in the midline just below the gill chamber. The body cavity, containing the vital organs, is situated behind the head in the lower anterior part of the body. The anus usually marks the posterior termination of the body cavity and most often occurs just in front of the base of the anal fin. The spinal cord and vertebral column continue from the posterior part of the head to the base of the tail fin, passing dorsal to the body cavity and through the caudal (tail) region behind the body cavity. Most of the body is of muscular tissue, a high proportion of which is necessitated by swimming. In the course of evolution this basic body plan has been modified repeatedly into the many varieties of fish shapes that exist today.
The skeleton forms an integral part of the fish’s locomotion system, as well as serving to protect vital parts. The internal skeleton consists of the skull bones (except for the roofing bones of the head, which are really part of the external skeleton), the vertebral column, and the fin supports (fin rays). The fin supports are derived from the external skeleton but will be treated here because of their close functional relationship to the internal skeleton. The internal skeleton of cyclostomes, sharks, and rays is of cartilage; that of many fossil groups and some primitive living fishes is mostly of cartilage but may include some bone. In place of the vertebral column, the earliest vertebrates had a fully developed notochord, a flexible stiff rod of viscous cells surrounded by a strong fibrous sheath. During the evolution of modern fishes the rod was replaced in part by cartilage and then by ossified cartilage. Sharks and rays retain a cartilaginous vertebral column; bony fishes have spool-shaped vertebrae that in the more primitive living forms only partially replace the notochord. The skull, including the gill arches and jaws of bony fishes, is fully, or at least partially, ossified. That of sharks and rays remains cartilaginous, at times partially replaced by calcium deposits but never by true bone.
The supportive elements of the fins (basal or radial bones or both) have changed greatly during fish evolution. Some of these changes are described in the section below (Evolution and paleontology). Most fishes possess a single dorsal fin on the midline of the back. Many have two and a few have three dorsal fins. The other fins are the single tail and anal fins and paired pelvic and pectoral fins. A small fin, the adipose fin, with hairlike fin rays, occurs in many of the relatively primitive teleosts (such as trout) on the back near the base of the caudal fin.
The skin of a fish must serve many functions. It aids in maintaining the osmotic balance, provides physical protection for the body, is the site of coloration, contains sensory receptors, and, in some fishes, functions in respiration. Mucous glands, which aid in maintaining the water balance and offer protection from bacteria, are extremely numerous in fish skin, especially in cyclostomes and teleosts. Since mucous glands are present in the modern lampreys, it is reasonable to assume that they were present in primitive fishes, such as the ancient Silurian and Devonian agnathans. Protection from abrasion and predation is another function of the fish skin, and dermal (skin) bone arose early in fish evolution in response to this need. It is thought that bone first evolved in skin and only later invaded the cartilaginous areas of the fish’s body, to provide additional support and protection. There is some argument as to which came first, cartilage or bone, and fossil evidence does not settle the question. In any event, dermal bone has played an important part in fish evolution and has different characteristics in different groups of fishes. Several groups are characterized at least in part by the kind of bony scales they possess.
Scales have played an important part in the evolution of fishes. Primitive fishes usually had thick bony plates or thick scales in several layers of bone, enamel, and related substances. Modern teleost fishes have scales of bone, which, while still protective, allow much more freedom of motion in the body. A few modern teleosts (some catfishes, sticklebacks, and others) have secondarily acquired bony plates in the skin. Modern and early sharks possessed placoid scales, a relatively primitive type of scale with a toothlike structure, consisting of an outside layer of enamel-like substance (vitrodentine), an inner layer of dentine, and a pulp cavity containing nerves and blood vessels. Primitive bony fishes had thick scales of either the ganoid or the cosmoid type. Cosmoid scales have a hard, enamel-like outer layer, an inner layer of cosmine (a form of dentine), and then a layer of vascular bone (isopedine). In ganoid scales the hard outer layer is different chemically and is called ganoin. Under this is a cosminelike layer and then a vascular bony layer. The thin, translucent bony scales of modern fishes, called cycloid and ctenoid (the latter distinguished by serrations at the edges), lack enameloid and dentine layers.
Skin has several other functions in fishes. It is well supplied with nerve endings and presumably receives tactile, thermal, and pain stimuli. Skin is also well supplied with blood vessels. Some fishes breathe in part through the skin, by the exchange of oxygen and carbon dioxide between the surrounding water and numerous small blood vessels near the skin surface.
Skin serves as protection through the control of coloration. Fishes exhibit an almost limitless range of colours. The colours often blend closely with the surroundings, effectively hiding the animal. Many fishes use bright colours for territorial advertisement or as recognition marks for other members of their own species, or sometimes for members of other species. Many fishes can change their colour to a greater or lesser degree, by movement of pigment within the pigment cells (chromatophores). Black pigment cells (melanophores), of almost universal occurrence in fishes, are often juxtaposed with other pigment cells. When placed beneath iridocytes or leucophores (bearing the silvery or white pigment guanine), melanophores produce structural colours of blue and green. These colours are often extremely intense, because they are formed by refraction of light through the needlelike crystals of guanine. The blue and green refracted colours are often relatively pure, lacking the red and yellow rays, which have been absorbed by the black pigment (melanin) of the melanophores. Yellow, orange, and red colours are produced by erythrophores, cells containing the appropriate carotenoid pigments. Other colours are produced by combinations of melanophores, erythrophores, and iridocytes.
The major portion of the body of most fishes consists of muscles. Most of the mass is trunk musculature, the fin muscles usually being relatively small. The caudal fin is usually the most powerful fin, being moved by the trunk musculature. The body musculature is usually arranged in rows of chevron-shaped segments on each side. Contractions of these segments, each attached to adjacent vertebrae and vertebral processes, bends the body on the vertebral joint, producing successive undulations of the body, passing from the head to the tail, and producing driving strokes of the tail. It is the latter that provides the strong forward movement for most fishes.
The digestive system, in a functional sense, starts at the mouth, with the teeth used to capture prey or collect plant foods. Mouth shape and tooth structure vary greatly in fishes, depending on the kind of food normally eaten. Most fishes are predacious, feeding on small invertebrates or other fishes and have simple conical teeth on the jaws, on at least some of the bones of the roof of the mouth, and on special gill arch structures just in front of the esophagus. The latter are throat teeth. Most predacious fishes swallow their prey whole, and the teeth are used for grasping and holding prey, for orienting prey to be swallowed (head first) and for working the prey toward the esophagus. There are a variety of tooth types in fishes. Some fishes, such as sharks and piranhas, have cutting teeth for biting chunks out of their victims. A shark’s tooth, although superficially like that of a piranha, appears in many respects to be a modified scale, while that of the piranha is like that of other bony fishes, consisting of dentine and enamel. Parrot fishes have beaklike mouths with short incisor-like teeth for breaking off coral and have heavy pavementlike throat teeth for crushing the coral. Some catfishes have small brushlike teeth, arranged in rows on the jaws, for scraping plant and animal growth from rocks. Many fishes (such as the Cyprinidae or minnows) have no jaw teeth at all but have very strong throat teeth.
Some fishes gather planktonic food by straining it from their gill cavities with numerous elongate stiff rods (gill rakers) anchored by one end to the gill bars. The food collected on these rods is passed to the throat, where it is swallowed. Most fishes have only short gill rakers that help keep food particles from escaping out the mouth cavity into the gill chamber.
Once reaching the throat, food enters a short, often greatly distensible esophagus, a simple tube with a muscular wall leading into a stomach. The stomach varies greatly in fishes, depending upon the diet. In most predacious fishes it is a simple straight or curved tube or pouch with a muscular wall and a glandular lining. Food is largely digested there and leaves the stomach in liquid form.
Between the stomach and the intestine, ducts enter the digestive tube from the liver and pancreas. The liver is a large, clearly defined organ. The pancreas may be embedded in it, diffused through it, or broken into small parts spread along some of the intestine. The junction between the stomach and the intestine is marked by a muscular valve. Pyloric ceca (blind sacs) occur in some fishes at this junction and have a digestive or absorptive function or both.
The intestine itself is quite variable in length, depending upon the fish’s diet. It is short in predacious forms, sometimes no longer than the body cavity, but long in herbivorous forms, being coiled and several times longer than the entire length of the fish in some species of South American catfishes. The intestine is primarily an organ for absorbing nutrients into the bloodstream. The larger its internal surface, the greater its absorptive efficiency, and a spiral valve is one method of increasing its absorption surface.
Sharks, rays, chimaeras, lungfishes, surviving chondrosteans, holosteans, and even a few of the more primitive teleosts have a spiral valve or at least traces of it in the intestine. Most modern teleosts have increased the area of the intestinal walls by having numerous folds and villi (fingerlike projections) somewhat like those in humans. Undigested substances are passed to the exterior through the anus in most teleost fishes. In lungfishes, sharks, and rays, it is first passed through the cloaca, a common cavity receiving the intestinal opening and the ducts from the urogenital system.
Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills. The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour. Water taken in continuously through the mouth passes backward between the gill bars and over the gill filaments, where the exchange of gases takes place. The gills are protected by a gill cover in teleosts and many other fishes but by flaps of skin in sharks, rays, and some of the older fossil fish groups. The blood capillaries in the gill filaments are close to the gill surface to take up oxygen from the water and to give up excess carbon dioxide to the water.
Most modern fishes have a hydrostatic (ballast) organ, called the swim bladder, that lies in the body cavity just below the kidney and above the stomach and intestine. It originated as a diverticulum of the digestive canal. In advanced teleosts, especially the acanthopterygians, the bladder has lost its connection with the digestive tract, a condition called physoclistic. The connection has been retained (physostomous) by many relatively primitive teleosts. In several unrelated lines of fishes, the bladder has become specialized as a lung or, at least, as a highly vascularized accessory breathing organ. Some fishes with such accessory organs are obligate air breathers and will drown if denied access to the surface, even in well-oxygenated water. Fishes with a hydrostatic form of swim bladder can control their depth by regulating the amount of gas in the bladder. The gas, mostly oxygen, is secreted into the bladder by special glands, rendering the fish more buoyant; the gas is absorbed into the bloodstream by another special organ, reducing the overall buoyancy and allowing the fish to sink. Some deep-sea fishes may have oils, rather than gas, in the bladder. Other deep-sea and some bottom-living forms have much-reduced swim bladders or have lost the organ entirely.
The swim bladder of fishes follows the same developmental pattern as the lungs of land vertebrates. There is no doubt that the two structures have the same historical origin in primitive fishes. More or less intermediate forms still survive among the more primitive types of fishes, such as the lungfishes Lepidosiren and Protopterus.
The circulatory, or blood vascular, system consists of the heart, the arteries, the capillaries, and the veins. It is in the capillaries that the interchange of oxygen, carbon dioxide, nutrients, and other substances such as hormones and waste products takes place. The capillaries lead to the veins, which return the venous blood with its waste products to the heart, kidneys, and gills. There are two kinds of capillary beds: those in the gills and those in the rest of the body. The heart, a folded continuous muscular tube with three or four saclike enlargements, undergoes rhythmic contractions and receives venous blood in a sinus venosus. It passes the blood to an auricle and then into a thick muscular pump, the ventricle. From the ventricle the blood goes to a bulbous structure at the base of a ventral aorta just below the gills. The blood passes to the afferent (receiving) arteries of the gill arches and then to the gill capillaries. There waste gases are given off to the environment, and oxygen is absorbed. The oxygenated blood enters efferent (exuant) arteries of the gill arches and then flows into the dorsal aorta. From there blood is distributed to the tissues and organs of the body. One-way valves prevent backflow. The circulation of fishes thus differs from that of the reptiles, birds, and mammals in that oxygenated blood is not returned to the heart prior to distribution to the other parts of the body.
The primary excretory organ in fishes, as in other vertebrates, is the kidney. In fishes some excretion also takes place in the digestive tract, skin, and especially the gills (where ammonia is given off). Compared with land vertebrates, fishes have a special problem in maintaining their internal environment at a constant concentration of water and dissolved substances, such as salts. Proper balance of the internal environment (homeostasis) of a fish is in a great part maintained by the excretory system, especially the kidney.
The kidney, gills, and skin play an important role in maintaining a fish’s internal environment and checking the effects of osmosis. Marine fishes live in an environment in which the water around them has a greater concentration of salts than they can have inside their body and still maintain life. Freshwater fishes, on the other hand, live in water with a much lower concentration of salts than they require inside their bodies. Osmosis tends to promote the loss of water from the body of a marine fish and absorption of water by that of a freshwater fish. Mucus in the skin tends to slow the process but is not a sufficient barrier to prevent the movement of fluids through the permeable skin. When solutions on two sides of a permeable membrane have different concentrations of dissolved substances, water will pass through the membrane into the more concentrated solution, while the dissolved chemicals move into the area of lower concentration (diffusion).
The kidney of freshwater fishes is often larger in relation to body weight than that of marine fishes. In both groups the kidney excretes wastes from the body, but the kidney of freshwater fishes also excretes large amounts of water, counteracting the water absorbed through the skin. Freshwater fishes tend to lose salt to the environment and must replace it. They get some salt from their food, but the gills and skin inside the mouth actively absorb salt from water passed through the mouth. This absorption is performed by special cells capable of moving salts against the diffusion gradient. Freshwater fishes drink very little water and take in little water with their food.
Marine fishes must conserve water, and therefore their kidneys excrete little water. To maintain their water balance, marine fishes drink large quantities of seawater, retaining most of the water and excreting the salt. Most nitrogenous waste in marine fishes appears to be secreted by the gills as ammonia. Marine fishes can excrete salt by clusters of special cells (chloride cells) in the gills.
There are several teleosts—for example, the salmon—that travel between fresh water and seawater and must adjust to the reversal of osmotic gradients. They adjust their physiological processes by spending time (often surprisingly little time) in the intermediate brackish environment.
Marine hagfishes, sharks, and rays have osmotic concentrations in their blood about equal to that of seawater and so do not have to drink water nor perform much physiological work to maintain their osmotic balance. In sharks and rays the osmotic concentration is kept high by retention of urea in the blood. Freshwater sharks have a lowered concentration of urea in the blood.
Endocrine glands secrete their products into the bloodstream and body tissues and, along with the central nervous system, control and regulate many kinds of body functions. Cyclostomes have a well-developed endocrine system, and presumably it was well developed in the early Agnatha, ancestral to modern fishes. Although the endocrine system in fishes is similar to that of higher vertebrates, there are numerous differences in detail. The pituitary, the thyroid, the suprarenals, the adrenals, the pancreatic islets, the sex glands (ovaries and testes), the inner wall of the intestine, and the bodies of the ultimobranchial gland make up the endocrine system in fishes. There are some others whose function is not well understood. These organs regulate sexual activity and reproduction, growth, osmotic pressure, general metabolic activities such as the storage of fat and the utilization of foodstuffs, blood pressure, and certain aspects of skin colour. Many of these activities are also controlled in part by the central nervous system, which works with the endocrine system in maintaining the life of a fish. Some parts of the endocrine system are developmentally, and undoubtedly evolutionarily, derived from the nervous system.
As in all vertebrates, the nervous system of fishes is the primary mechanism coordinating body activities, as well as integrating these activities in the appropriate manner with stimuli from the environment. The central nervous system, consisting of the brain and spinal cord, is the primary integrating mechanism. The peripheral nervous system, consisting of nerves that connect the brain and spinal cord to various body organs, carries sensory information from special receptor organs such as the eyes, internal ears, nares (sense of smell), taste glands, and others to the integrating centres of the brain and spinal cord. The peripheral nervous system also carries information via different nerve cells from the integrating centres of the brain and spinal cord. This coded information is carried to the various organs and body systems, such as the skeletal muscular system, for appropriate action in response to the original external or internal stimulus. Another branch of the nervous system, the autonomic nervous system, helps to coordinate the activities of many glands and organs and is itself closely connected to the integrating centres of the brain.
The brain of the fish is divided into several anatomical and functional parts, all closely interconnected but each serving as the primary centre of integrating particular kinds of responses and activities. Several of these centres or parts are primarily associated with one type of sensory perception, such as sight, hearing, or smell (olfaction).
The sense of smell is important in almost all fishes. Certain eels with tiny eyes depend mostly on smell for location of food. The olfactory, or nasal, organ of fishes is located on the dorsal surface of the snout. The lining of the nasal organ has special sensory cells that perceive chemicals dissolved in the water, such as substances from food material, and send sensory information to the brain by way of the first cranial nerve. Odour also serves as an alarm system. Many fishes, especially various species of freshwater minnows, react with alarm to a chemical released from the skin of an injured member of their own species.
Many fishes have a well-developed sense of taste, and tiny pitlike taste buds or organs are located not only within their mouth cavities but also over their heads and parts of their body. Catfishes, which often have poor vision, have barbels (“whiskers”) that serve as supplementary taste organs, those around the mouth being actively used to search out food on the bottom. Some species of naturally blind cave fishes are especially well supplied with taste buds, which often cover most of their body surface.
Sight is extremely important in most fishes. The eye of a fish is basically like that of all other vertebrates, but the eyes of fishes are extremely varied in structure and adaptation. In general, fishes living in dark and dim water habitats have large eyes, unless they have specialized in some compensatory way so that another sense (such as smell) is dominant, in which case the eyes will often be reduced. Fishes living in brightly lighted shallow waters often will have relatively small but efficient eyes. Cyclostomes have somewhat less elaborate eyes than other fishes, with skin stretched over the eyeball perhaps making their vision somewhat less effective. Most fishes have a spherical lens and accommodate their vision to far or near subjects by moving the lens within the eyeball. A few sharks accommodate by changing the shape of the lens, as in land vertebrates. Those fishes that are heavily dependent upon the eyes have especially strong muscles for accommodation. Most fishes see well, despite the restrictions imposed by frequent turbidity of the water and by light refraction.
Fossil evidence suggests that colour vision evolved in fishes more than 300 million years ago, but not all living fishes have retained this ability. Experimental evidence indicates that many shallow-water fishes, if not all, have colour vision and see some colours especially well, but some bottom-dwelling shore fishes live in areas where the water is sufficiently deep to filter out most if not all colours, and these fishes apparently never see colours. When tested in shallow water, they apparently are unable to respond to colour differences.
Sound perception and balance are intimately associated senses in a fish. The organs of hearing are entirely internal, located within the skull, on each side of the brain and somewhat behind the eyes. Sound waves, especially those of low frequencies, travel readily through water and impinge directly upon the bones and fluids of the head and body, to be transmitted to the hearing organs. Fishes readily respond to sound; for example, a trout conditioned to escape by the approach of fishermen will take flight upon perceiving footsteps on a stream bank even if it cannot see a fisherman. Compared with humans, however, the range of sound frequencies heard by fishes is greatly restricted. Many fishes communicate with each other by producing sounds in their swim bladders, in their throats by rasping their teeth, and in other ways.
A fish or other vertebrate seldom has to rely on a single type of sensory information to determine the nature of the environment around it. A catfish uses taste and touch when examining a food object with its oral barbels. Like most other animals, fishes have many touch receptors over their body surface. Pain and temperature receptors also are present in fishes and presumably produce the same kind of information to a fish as to humans. Fishes react in a negative fashion to stimuli that would be painful to human beings, suggesting that they feel a sensation of pain.
An important sensory system in fishes that is absent in other vertebrates (except some amphibians) is the lateral line system. This consists of a series of heavily innervated small canals located in the skin and bone around the eyes, along the lower jaw, over the head, and down the mid-side of the body, where it is associated with the scales. Intermittently along these canals are located tiny sensory organs (pit organs) that apparently detect changes in pressure. The system allows a fish to sense changes in water currents and pressure, thereby helping the fish to orient itself to the various changes that occur in the physical environment.
Rapid strata formation in soft sand (field evidence).
Photo of strata formation in soft sand on a beach, created by tidal action of the sea.
Formed in a single, high tidal event.
This natural example of rapid, simultaneous stratification refutes the Superposition Principle and the Principle of Lateral Continuity.
Superposition only applies on a rare occasion of sedimentary deposits in perfectly, still water. Superposition is required for the long evolutionary timescale, but the evidence shows it is not the general rule, as was once believed. Most sediment is laid down in moving water, where particle segregation is the rule, resulting in the simultaneous deposition of strata/layers as shown in the photo.
Where the water movement is very turbulent, violent, or catastrophic, great depths of stratified sediment can be laid down in a short time. Certainly not the many millions of years assumed by evolutionists.
The composition of strata formed in any deposition event. is related to whatever materials are in the sediment mix. Whatever is in the mix will be automatically sorted into strata/layers. It could be sand, or material added from mud slides, erosion of chalk deposits, volcanic ash etc. Any organic material (potential fossils) will also be sorted and buried within the rapidly, formed strata.
See many other examples of rapid stratification with geological features: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Stratified, soft sand deposit. demonstrates the rapid, stratification principle.
Important, field evidence which supports the work of the eminent, sedimentologist Dr Guy Berthault MIAS - Member of the International Association of Sedimentologists.
(Dr Berthault's experiments (www.sedimentology.fr/)
And also the experimental work of Dr M.E. Clark (Professor Emeritus, U of Illinois @ Urbana), Andrew Rodenbeck and Dr. Henry Voss, (www.ianjuby.org/sedimentation/)
Location: Sandown beach, Isle of Wight. Formed 07/12/2017, This field evidence demonstrates that multiple strata in sedimentary deposits do not need millions of years to form and can be formed rapidly. This natural example confirms the principle demonstrated by the sedimentation experiments carried out by Dr Guy Berthault and other sedimentologists. It calls into question the standard, multi-million year dating of sedimentary rocks, and the dating of fossils by depth of burial or position in the strata.
Mulltiple strata/layers and several, geological features are evident in this example.
Dr Berthault's experiments (www.sedimentology.fr/) and other experiments (www.ianjuby.org/sedimentation/) and field studies of floods and volcanic action show that, rather than being formed by gradual, slow deposition of sucessive layers superimposed upon previous layers, with the strata or layers representing a particular timescale, particle segregation in moving water or airborne particles can form strata or layers very quickly, frequently, in a single event.
And, most importantly, lower strata are not older than upper strata, they are the same age, having been created in the same sedimentary episode.
Such field studies confirm experiments which have shown that there is no longer any reason to conclude that strata/layers in sedimentary rocks relate to different geological eras and/or a multi-million year timescale. www.youtube.com/watch?v=5PVnBaqqQw8&feature=share&.... they also show that the relative position of fossils in rocks is not indicative of an order of evolutionary succession. Obviously, the uniformitarian principle, on which the geologic column is based, can no longer be considered valid. And the multi-million, year dating of sedimentary rocks and fossils needs to be reassessed. Rapid deposition of stratified sediments also explains the enigma of polystrate fossils, i.e. large fossils that intersect several strata. In some cases, tree trunk fossils are found which intersect the strata of sedimentary rock up to forty feet in depth. upload.wikimedia.org/wikipedia/commons/thumb/0/08/Lycopsi... They must have been buried in stratified sediment in a short time (certainly not millions, thousands, or even hundreds of years), or they would have rotted away. youtu.be/vnzHU9VsliQ
In fact, the vast majority of fossils are found in good, intact condition, which is testament to their rapid burial. You don't get good fossils from gradual burial, because they would be damaged or destroyed by decay, predation or erosion. The existence of so many fossils in sedimentary rock on a global scale is stunning evidence for the rapid depostion of sedimentary rock as the general rule. It is obvious that all rock containing good intact fossils was formed from sediment laid down in a very short time, not millions, or even thousands of years.
See set of photos of other examples of rapid stratification: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Carbon dating of coal should not be possible if it is millions of years old, yet significant amounts of Carbon 14 have been detected in coal and other fossil material, which indicates that it is less than 50,000 years old. www.ldolphin.org/sewell/c14dating.html
www.grisda.org/origins/51006.htm
Evolutionists confidently cite multi-million year ages for rocks and fossils, but what most people don't realise is that no one actually knows the age of sedimentary rocks or the fossils found within them. So how are evolutionists so sure of the ages they so confidently quote? The astonishing thing is they aren't. Sedimentary rocks cannot be dated by radiometric methods*, and fossils can only be dated to less than 50,000 years with Carbon 14 dating. The method evolutionists use is based entirely on assumptions. Unbelievably, fossils are dated by the assumed age of rocks, and rocks are dated by the assumed age of fossils, that's right ... it is known as circular reasoning.
* Regarding the radiometric dating of igneous rocks, which is claimed to be relevant to the dating of sedimentary rocks, in an occasional instance there is an igneous intrusion associated with a sedimentary deposit -
Prof. Aubouin says in his Précis de Géologie: "Each radioactive element disintegrates in a characteristic and constant manner, which depends neither on the physical state (no variation with pressure or temperature or any other external constraint) nor on the chemical state (identical for an oxide or a phosphate)."
"Rocks form when magma crystallizes. Crystallisation depends on pressure and temperature, from which radioactivity is independent. So, there is no relationship between radioactivity and crystallisation.
Consequently, radioactivity doesn't date the formation of rocks. Moreover, daughter elements contained in rocks result mainly from radioactivity in magma where gravity separates the heavier parent element, from the lighter daughter element. Thus radiometric dating has no chronological signification." Dr. Guy Berthault www.sciencevsevolution.org/Berthault.htm
Visit the fossil museum:
www.flickr.com/photos/101536517@N06/sets/72157641367196613/
Just how good are peer reviews of scientific papers?
www.sciencemag.org/content/342/6154/60.full
www.examiner.com/article/want-to-publish-science-paper-ju...
The neo-Darwinian idea that the human genome consists entirely of an accumulation of billions of mutations is, quite obviously, completely bonkers. Nevertheless, it is compulsorily taught in schools and universities as 'science'.
Rapid strata formation in soft sand (field evidence).
Photo of strata formation in soft sand on a beach, created by tidal action of the sea.
Formed in a single, high tidal event. Stunning evidence which displays multiple strata/layers.
Why this is so important ....
It has long been assumed, ever since the 17th century, that layers/strata observed in sedimentary rocks were built up gradually, layer upon layer, over many years. It certainly seemed logical at the time, from just looking at rocks, that lower layers would always be older than the layers above them, i.e. that lower layers were always laid down first followed, in time, by successive layers on top.
This was assumed to be true and became known as the superposition principle.
It was also assumed that a layer comprising a different material from a previous layer, represented a change in environmental conditions/factors.
These changes in composition of layers or strata were considered to represent different, geological eras on a global scale, spanning millions of years. This formed the basis for the Geologic Column, which is used to date rocks and also fossils. The evolutionary, 'fossil record' was based on the vast ages and assumed geological eras of the Geologic Column.
There was also circular reasoning applied with the assumed age of 'index' fossils (based on evolutionary beliefs & preconceptions) used to date strata in the Geologic Column. Dating strata from the assumed age of (index) fossils is known as Biostratigraphy.
We now know that, although these assumptions seemed logical, they are not supported by the evidence.
At the time, the mechanics of stratification were not properly known or studied.
An additional factor was that this assumed superposition and uniformitarian model became essential, with the wide acceptance of Darwinism, for the long ages required for progressive microbes-to-human evolution. There was no incentive to question or challenge the superposition, uniformitarian model, because the presumed, fossil 'record' had become dependant on it, and any change in the accepted model would present devastating implications for Darwinism.
This had the unfortunate effect of linking the study of geology so closely to Darwinism, that any study independent of Darwinian considerations was effectively stymied. This link of geology with Darwinian preconceptions is known as biostratigraphy.
Some other field evidence, in various situations, can be observed here: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
and also in the links to stunning, experimental evidence, carried out by sedimentologists, given later.
_______________________________________________
GEOLOGIC PRINCIPLES (established by Nicholas Steno in the 17th Century):
What Nicolas Steno believed about strata formation is the basis of the principle of Superposition and the principle of Original Horizontality.
dictionary.sensagent.com/Law_of_superposition/en-en/
“Assuming that all rocks and minerals had once been fluid, Nicolas Steno reasoned that rock strata were formed when particles in a fluid such as water fell to the bottom. This process would leave horizontal layers. Thus Steno's principle of original horizontality states that rock layers form in the horizontal position, and any deviations from this horizontal position are due to the rocks being disturbed later.”)
BEDDING PLANES.
'Bedding plane' describes the surface in between each stratum which are formed during sediment deposition.
science.jrank.org/pages/6533/Strata.html
“Strata form during sediment deposition, that is, the laying down of sediment. Meanwhile, if a change in current speed or sediment grain size occurs or perhaps the sediment supply is cut off, a bedding plane forms. Bedding planes are surfaces that separate one stratum from another. Bedding planes can also form when the upper part of a sediment layer is eroded away before the next episode of deposition. Strata separated by a bedding plane may have different grain sizes, grain compositions, or colours. Sometimes these other traits are better indicators of stratification as bedding planes may be very subtle.”
______________________________________________
Several catastrophic events, flash floods, volcanic eruptions etc. have forced Darwinian, influenced geologists to admit to rapid stratification in some instances. However they claim it is a rare phenomenon, which they have known about for many years, and which does nothing to invalidate the Geologic Column, the fossil record, evolutionary timescale, or any of the old assumptions regarding strata formation, sedimentation and the superposition principle. They fail to face up to the fact that rapid stratification is not an extraordinary phenonemon, but rather the prevailing and normal mechanism of sedimentary deposition whenever and wherever there is moving, sediment-laden water. The experimental evidence demonstrates the mechanism and a mass of field evidence in normal (non-catastrophic) conditions shows it is a normal everyday occurrence.
It is clear from the experimental evidence that the usual process of stratification is - that strata are not formed by horizontal layers being laid on top of each other in succession, as was assumed. But by sediment being sorted in the flowing water and laid down diagonally in the direction of flow. See diagram:
www.flickr.com/photos/truth-in-science/39821536092/in/dat...
The field evidence (in the image) presented here - of rapid, simultaneous stratification refutes the Superposition Principle and the Principle of Lateral Continuity.
We now know, the Superposition Principle only applies on a rare occasion where sedimentary deposits are laid down in still water.
Superposition is required for the long evolutionary timescale, but the evidence shows it is not the general rule, as was once believed. Most sediment is laid down in moving water, where particle segregation is the general rule, resulting in the simultaneous deposition of strata/layers as shown in the photo.
See many other examples of rapid stratification (with geological features): www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Rapid, simultaneous formation of layers/strata, through particle segregation in moving water, is so easily created it has even been described by sedimentologists (working on flume experiments) as a law ...
"Upon filling the tank with water and pouring in sediments, we immediately saw what was to become the rule: The sediments sorted themselves out in very clear layers. This became so common that by the end of two weeks, we jokingly referred to Andrew's law as "It's difficult not to make layers," and Clark's law as "It's easy to make layers." Later on, I proposed the "law" that liquefaction destroys layers, as much to my surprise as that was." Ian Juby, www.ianjuby.org/sedimentation/
The field example in the photo is the result of normal, everyday tidal action formed in a single incident,
Where the water current or movement is more turbulent, violent, or catastrophic, great depths (many metres) of stratified sediment can be laid down in a short time. Certainly not the many millions of years assumed by evolutionists.
The composition of strata formed in any deposition event. is related to whatever materials are in the sediment mix, not to any particular timescale. Whatever is in the mix will be automatically sorted into strata/layers. It could be sand, or other material added from mud slides, erosion of chalk deposits, coastal erosion, volcanic ash etc. Any organic material (potential fossils), alive or dead, engulfed by, or swept into, a turbulent sediment mix, will also be sorted and buried within the rapidly, forming layers.
See many other examples of rapid stratification with geological features: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Stratified, soft sand deposit. demonstrates the rapid, stratification principle.
Important, field evidence which supports the work of the eminent, sedimentologist Dr Guy Berthault MIAS - Member of the International Association of Sedimentologists.
(Dr Berthault's experiments (www.sedimentology.fr/)
And also the experimental work of Dr M.E. Clark (Professor Emeritus, U of Illinois @ Urbana), Andrew Rodenbeck and Dr. Henry Voss, (www.ianjuby.org/sedimentation/)
Location: Yaverland, Isle of Wight. photographed 04/06/2018, formed several months earlier and in the early stages of consolidation.
This field evidence demonstrates that multiple strata in sedimentary deposits do not need millions of years to form and can be formed rapidly. This natural example confirms the principle demonstrated by the sedimentation experiments carried out by Dr Guy Berthault and other sedimentologists. It calls into question the standard, multi-million year dating of sedimentary rocks, and the dating of fossils by depth of burial or position in the strata.
Mulltiple strata/layers are evident in this example.
Dr Berthault's experiments (www.sedimentology.fr/) and other experiments (www.ianjuby.org/sedimentation/) and field studies of floods and volcanic action show that, rather than being formed by gradual, slow deposition of sucessive layers superimposed upon previous layers, with the strata or layers representing a particular timescale, particle segregation in moving water or airborne particles can form strata or layers very quickly, frequently, in a single event.
And, most importantly, lower strata are not older than upper strata, they are the same age, having been created in the same sedimentary episode.
Such field studies confirm experiments which have shown that there is no longer any reason to conclude that strata/layers in sedimentary rocks relate to different geological eras and/or a multi-million year timescale. www.youtube.com/watch?v=5PVnBaqqQw8&feature=share&.... they also show that the relative position of fossils in rocks is not indicative of an order of evolutionary succession. Obviously, the uniformitarian principle, on which the geologic column is based, can no longer be considered valid. And the multi-million, year dating of sedimentary rocks and fossils needs to be reassessed. Rapid deposition of stratified sediments also explains the enigma of polystrate fossils, i.e. large fossils that intersect several strata. In some cases, tree trunk fossils are found which intersect the strata of sedimentary rock up to forty feet in depth. upload.wikimedia.org/wikipedia/commons/thumb/0/08/Lycopsi... They must have been buried in stratified sediment in a short time (certainly not millions, thousands, or even hundreds of years), or they would have rotted away. youtu.be/vnzHU9VsliQ
In fact, the vast majority of fossils are found in good, intact condition, which is testament to their rapid burial. You don't get good fossils from gradual burial, because they would be damaged or destroyed by decay, predation or erosion. The existence of so many fossils in sedimentary rock on a global scale is stunning evidence for the rapid depostion of sedimentary rock as the general rule. It is obvious that all rock containing good intact fossils was formed from sediment laid down in a very short time, not millions, or even thousands of years.
See set of photos of other examples of rapid stratification: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Carbon dating of coal should not be possible if it is millions of years old, yet significant amounts of Carbon 14 have been detected in coal and other fossil material, which indicates that it is less than 50,000 years old. www.ldolphin.org/sewell/c14dating.html
www.grisda.org/origins/51006.htm
Evolutionists confidently cite multi-million year ages for rocks and fossils, but what most people don't realise is that no one actually knows the age of sedimentary rocks or the fossils found within them. So how are evolutionists so sure of the ages they so confidently quote? The astonishing thing is they aren't. Sedimentary rocks cannot be dated by radiometric methods*, and fossils can only be dated to less than 50,000 years with Carbon 14 dating. The method evolutionists use is based entirely on assumptions. Unbelievably, fossils are dated by the assumed age of rocks, and rocks are dated by the assumed age of fossils, that's right ... it is known as circular reasoning.
* Regarding the radiometric dating of igneous rocks, which is claimed to be relevant to the dating of sedimentary rocks, in an occasional instance there is an igneous intrusion associated with a sedimentary deposit -
Prof. Aubouin says in his Précis de Géologie: "Each radioactive element disintegrates in a characteristic and constant manner, which depends neither on the physical state (no variation with pressure or temperature or any other external constraint) nor on the chemical state (identical for an oxide or a phosphate)."
"Rocks form when magma crystallizes. Crystallisation depends on pressure and temperature, from which radioactivity is independent. So, there is no relationship between radioactivity and crystallisation.
Consequently, radioactivity doesn't date the formation of rocks. Moreover, daughter elements contained in rocks result mainly from radioactivity in magma where gravity separates the heavier parent element, from the lighter daughter element. Thus radiometric dating has no chronological signification." Dr. Guy Berthault www.sciencevsevolution.org/Berthault.htm
"A team of Russian sedimentologists directed by Alexander Lalomov (Russian Academy of Sciences’ Institute of Ore Deposits) applied paleohydraulic analyses to geological formations in Russia. One example is the publication of a report in 2007 by the Lithology and Mineral Resources journal of the Russian Academy of Sciences. It concerns the Crimean Peninsular. It shows that the time of sedimentation of the sequence studied corresponds to a virtually instantaneous episode whilst according to stratigraphy it took several millions of years. Moreover, a recent report concerning the North-West Russian plateau in the St. Petersburg region shows that the time of sedimentation was much shorter than that attributed to it by the stratigraphic time-scale: 0.05% of the time."
www.sciencevsevolution.org/Berthault.htm
Rapid strata formation and rapid erosion at Mount St Helens.
slideplayer.com/slide/5703217/18/images/28/Rapid+Strata+F...
Visit the fossil museum:
www.flickr.com/photos/101536517@N06/sets/72157641367196613/
Just how good are peer reviews of scientific papers?
www.sciencemag.org/content/342/6154/60.full
www.examiner.com/article/want-to-publish-science-paper-ju...
The neo-Darwinian idea that the human genome consists entirely of an accumulation of billions of mutations is, quite obviously, completely bonkers. Nevertheless, it is compulsorily taught in schools and universities as 'science'.
"Greetings, X-Men. I bid you welcome to the site of your final battleground. You are going to die here, mutants. And neither your powers nor all your skills can save you from my wrath! Look on me, X-Men for I am your oldest, deadliest foe. Master of the legion of evil mutants -- and soon to be lord of all the world! I -- am -- Magneto!!"
— Magneto, X-Men Vol 1 104
Character Publication History
Magneto (/mæɡˈniːtoʊ/; birth name: Max Eisenhardt; (alias: Erik Lehnsherr and Magnus) is a character appearing in American comic books published by Marvel Comics, commonly in association with the X-Men. Created by writer Stan Lee and artist/co-writer Jack Kirby, the character first appeared in The X-Men #1 (cover-dated September 1963) as an adversary of the X-Men.
Magneto is a powerful mutant, one of a fictional subspecies of humanity born with superhuman abilities, who has the ability to generate and control magnetic fields. Magneto regards mutants as evolutionarily superior to humans and rejects the possibility of peaceful human-mutant coexistence; he initially aimed to conquer the world to enable mutants, whom he refers to as Homo superior, to replace humans as the dominant species, and occasionally advocated for human genocide.
Writers have since fleshed out his origins and motivations, revealing him to be a Holocaust survivor whose extreme methods and cynical philosophy derive from his "Never again" determination to protect mutants from suffering a similar fate to the European Jews at the hands of a world that fears and persecutes them.
He was once a friend of Professor X, the leader of the X-Men, but their different philosophies sometimes cause a rift in their friendship. Magneto's role in comics has progressed from supervillain to antihero to superhero, having served as an occasional ally and member of the X-Men, even leading the New Mutants for a time as headmaster of the Xavier School for Gifted Youngsters.
Writer Chris Claremont, who originated Magneto's backstory, modeled the character on then-Israeli opposition leader Menachem Begin.
Ian McKellen has portrayed Magneto in various films since X-Men in 2000, while Michael Fassbender has portrayed a younger version of the character in the prequel films since X-Men: First Class in 2011. Both actors portrayed their respective incarnations in X-Men: Days of Future Past. Magneto appears in X-Men: The Animated Series (1992) voiced by David Hemblen and its sequel X-Men '97 (2024) voiced by Matthew Waterson.
Magneto first appeared in the debut issue of The X-Men in 1963. Since the 1960s, Magneto has appeared in The Uncanny X-Men, X-Men, Astonishing X-Men, Alpha Flight, Cable, Excalibur, The New Mutants, various X-Men miniseries, and many other Marvel titles. His first solo title was a one-shot special, Magneto: The Twisting of a Soul #0 (Sept. 1993), published when the character returned from a brief absence; it reprinted Magneto-based stories from Classic X-Men #12 and 19 (Aug. 1987 and March 1988), by writer Chris Claremont and artist John Bolton.
When asked about his approach to Magneto, Jack Kirby stated, "I saw my villains not as villains. I knew villains had to come from somewhere and they came from people. My villains were people that developed problems." In a 2008 interview, Stan Lee said he "did not think of Magneto as a bad guy. He just wanted to strike back at the people who were so bigoted and racist...he was trying to defend the mutants, and because society was not treating them fairly he was going to teach society a lesson. He was a danger of course...but I never thought of him as a villain." In the same interview, he also revealed that he originally planned for Magneto to be the brother of his nemesis Professor X.
Writer Chris Claremont stated that Menachem Begin was an inspiration for Magneto's development, as David Ben-Gurion was for Professor X. "An equivalent analogy could be made to [Israeli prime minister] Menachem Begin as Magneto, evolving through his life from a terrorist in 1947 to a winner of the Nobel Peace Prize 30 years later."
Claremont also said "My resonance to Magneto and Xavier was borne more out of the Holocaust. It was coming face to face with evil, and how do you respond to it? In Magneto's case it was violence begets violence. In Xavier's it was the constant attempt to find a better way..."
Magneto's first original title was the four-issue miniseries Magneto (Nov. 1996-Feb. 1997), by writers Peter Milligan and Jorge Gonzalez, and penciller Kelley Jones. In the miniseries, Magneto had been de-aged and suffered from amnesia, calling himself Joseph; it was later revealed that Joseph was a younger clone of Magneto.
Later, Magneto became ruler of the nation Genosha and then appeared in two miniseries; Magneto Rex (written by Joe Pruett and drawn by Brandon Peterson) and Magneto: Dark Seduction (written by Fabian Nicieza and drawn by Roger Cruz).
A trade paperback novel detailing Magneto's childhood, X-Men: Magneto Testament was written by Greg Pak and released in September 2008. Pak based Magneto Testament on accounts from Holocaust survivors. Before the publication of X-Men: Magneto Testament, Magneto's personal background and history were invented in The Uncanny X-Men #150 (Aug. 1981).
He was portrayed as a Jewish Holocaust survivor; while searching for his wife Magda, a Sintesa, Magneto maintained a cover identity as a Sinto. This created confusion among some readers as to Magneto's heritage, until his Jewish background was confirmed in Magneto: Testament.
Origin
The man that would become known as "Magneto" was born Max Eisenhardt in Germany during the 1920's to a middle class Jewish family. His father, Jakob Eisenhardt, was a World War I veteran and a proud German. The family struggled against discrimination and hardship during the Nazi's rise to power, the Nuremberg laws, and Kristallnacht. In the early 1930's, the family fled to Poland, where they were captured during the Nazi invasion and sent to the Warsaw Ghetto. They managed to escape the ghetto, but were captured again. Max's mother, father, and sister were executed, but Max survived (potentially thanks to an early manifestation of his powers) and was sent to the Auschwitz concentration camp.
There, Max became a Sonderkommando, forced to dispose of gas chamber victims. While at the camp, Max was reunited with a girl he had fallen in love with during his school days named Magda. Max and and Magda escaped when Auschwitz was liberated and were soon married. They moved to the Ukrainian city of Vinnytsia, where they started their new lives together. Max adopted the name "Magnus" and Magda gave birth to their daughter who they named Anya.
Magnus worked as a carpenter to support the family and for a time they lived happily. One night Magnus was attacked and instinctively lashed out with his mutant powers of magnetism (which had never surfaced before due to a bout of scarlet fever as a child), killing the attackers. Later that evening, he returned home to find his house on fire, with Anya trapped inside. Magnus rushed inside to rescue her but he was too late. Enraged at the death of his beloved daughter, he used his new powers to kill the surrounding mob that started the fire. Magda, terrified of her husband's strange abilities, fled to the forest and never saw her husband again.
Magda made her way to Wundagore Mountain, where she gave birth to twins Pietro and Wanda (who would grew up to be Quicksilver and Scarlet Witch, respectively). Magda later disappeared, presumed deceased. During the next few years Magnus had an identity forger named Greg Odekirk create him a new identity, reinventing himself as a gypsy named "Erik Magnus Lehnsherr". It was while using this identity that he went to Israel to help at a psychiatric hospital. There, he met Professor Charles Xavier. The two became fast friends, playing chess and having intellectual debates about mutation and the future of mankind.
When Baron Wolfgang Von Strucker attacked a young patient named Gabrielle Haller, Xavier and Magnus used their powers in order to save her. Following the battle, Charles and Magnus realized they had very differing ideologies. Magnus disappeared and the two friends would not meet again for many years. During the next few years, Magnus worked for the CIA hunting Nazis, but this association ended when they murdered a girl he was becoming close to. Magnus would not be seen again until he became the mutant known as Magneto.
Character Evolution
In his initial appearances, Magneto was portrayed as a would-be tyrant, who had a desire to punish all human and would often abuse his subjects (he physically abused Toad, one of the members of the Brotherhood of Evil Mutants, while Scarlet Witch was psychologically tormented into obedience, as Magneto saved her life in the past). Eventually, (as Marvel did with many of their long-lasting villains over the years) Magneto was given a more humanized portrayal as a Holocaust survivor who wanted to ensure that mutants would not suffer the same fate his family did for being born different.
Magneto has long been the face of mutant separatism, in opposition to Charles Xavier's ideal of coexistence with humanity. Believing that mutants are the next stage in human evolution, he sought to assert their dominance over the planet and its inhabitants. This was Magneto's means of assuring the survival of his people in a world that hates and fears them for there very existence. Though not a hero, Magneto is charismatic, noble, and wise. His long and turbulent friendship with Charles Xavier has been a cornerstone for both men's lives, as a rivalry that has lasted decades.
Major Story Arcs
War on Humanity
After years of lying low, Magnus eventually resurfaced, now using the identity of "Magneto" bursting into the public eye. He attacked Cape Citadel, but was stopped by the original X-Men, a confrontation that would spark a decades long rivalry. Some months later, Magneto was seen leading a team of mutants witch he mockingly named the Brotherhood of "Evil" Mutants. This group consisted of a few mutants including, the Scarlet Witch and Quicksilver. These young mutants where actually his daughter and son, but none of them knew at the time.
Demanding not merely equal rights, the Brotherhood sought supremacy for mutant-kind. Their vicious attacks against humans led them to attract the attention of Professor Xavier and his X-Men, whom where often able to repel the group. Magneto did however not just fight against the X-Men but many other superhero groups such as the Avengers and the Fantastic Four. During one of Magneto's plans, Professor Xavier sought the help of the superheroes team known as the Defenders. Magneto had made a new mutant-like entity named Alpha the Ultimate Mutant.
This mutant was made by Magneto to help further his cause. The creature however turned on him and returned Magneto to the age of an infant. The child was brought into the care of Charles Xavier, who brought him over to his former lover Moira MacTaggert. She took care of the infant Magneto for some months before he was restored to his prime age as a young man by the Shi'ar agent Eric the Red. Although shaken by the events and perhaps changed for good, Magneto still sought out to win his war against humanity. Now once again in his physical prime (and stronger than before), Magneto battled the X-Men on Muir Island before disappearing. He would later return to capture the X-Men, but was badly injured after being attacked by Wolverine. The injuries forced Magneto to flee, allowing the X-Men to thwart his plan.
Reformation Period
During a particularly heated battle with the X-Men, Magneto wounds and nearly kills Kitty Pryde (then only fourteen). Stricken with the revelation that he’s become a horrific extremist, willing to murder even children to achieve his goals, Magneto renounces his terrorist ways. He seeks out his former wife Magda and learns of her death, but also the truth about Scarlet Witch and Quicksilver: that they are his children. While the pair accept that he’s their father, they reject Magneto's leadership for his abusive treatment of them over their years in the Brotherhood.
Time would eventually heal their wounds, and they would come to a grudging acceptance of him. Magneto joins the X-Men after being persuaded to give human/mutant co-existence a chance by Professor Xavier. This comes at a time when Charles is badly injured in battle and Magneto takes over the reign of his school, teaching young mutants to control their powers and use them for the betterment of both humans and mutants. He started teaching the New Mutants and fought alongside the X-men. This, at first was very difficult for many of the team-members, since they had done battle against Magneto more then once.
However, Magneto proved to be a valuable ally and the X-Men started to trust him. Even Wolverine, previously extremely wary of the mutant leader, grew to accept him. It appeared Magneto was truly a changed man, and even allowed himself to be put on trial on France. However, the trial was interrupted by a battle before it could be finished.
When part of Magneto's old Asteroid M base crashed down onto the Earth, he went to survey one of the impact sites and destroy any dangerous weaponry that might be inside. However, he was soon confronted by the Avengers, who mistakenly believed him to be there for sinister purposes. Despite trying to explain himself, Magneto ended up fighting against the heroes, which only got worse when the X-Men arrived to back him up. The situation would grow even more complicated when the Soviet Super Soldiers joined the fray, seeking to arrest Magneto for a volcanic eruption he'd previously caused in Russia. The X-Men themselves were concerned by Magneto's actions, and Wolverine began to suspect that Erik might be returning to his old ways. After finding his old helmet in the ruins of Asteroid M, Magneto began to feel tempted by his past, believing that he could use the old mind control circuits within to brainwash the planet's population so that all feelings of bigotry would be erased. When asked his thoughts on the situation, Captain America argued that using mind control to change minds was unethical, and something that would violate the very concept of freedom Magneto was striving for. After realizing that there was no anti-mutant bigotry in Captain America's heart, Magneto surrendered himself to the Avengers and allowed himself to be put on trial once again. When Captain Marvel discovered that the head judge presiding over the case was revealed to be an anti-mutant bigot, Magneto decided to use his helmet to alter the man's mind and remove his prejudiced thoughts. After finally destroying his helmet and being found innocent of his past crimes, a largely surprised Magneto now felt like a free man once more who had made a change for the good.
However, certain events would reverse a great many of those feelings soon. The Mutant Massacre occurred, in which many of the Morlocks would be killed by the mutant-hunting Marauders. Some months later, during the events of the Fall of the Mutants, Magneto's star pupils, Cypher, was killed by a human. This incident and the fact that he could not have protected an innocent young mutant under his care, started breaking Magneto up. At this time, he also lost contact with the X-Men when the team went to Australia.
In finding security for his New Mutant students, Magneto went as far as joining longtime X-Men rivals the Hellfire Club in hope of providing the security for them that he could not give. The New Mutants, however, wanted nothing to do with Magneto anymore, feeling he had betrayed them. Magneto, now angry, left the New Mutants and, after this, many of his human-hating ways resurfaced. Ultimately, Magneto would view his role as leader of the X-Men and teacher of the New Mutants as a failure on his part and he retired to Asteroid M to live in seclusion.
Mutant Separatism
While living in isolation, a group of mutants led by Fabian Cortez calling themselves the Acolytes approached Magneto asking for his leadership. Magneto decided that his best course of action would be to create a nation for mutants unto themselves and goes so far as declaring Asteroid M such a nation. Magneto even made the move to defend himself against further attacks of the human race by taking up the armed missiles of a Russian submarine he sunk years ago.
The X-Men responded accordingly by assaulting Magneto and his group of mutants. While the X-man Rogue tried to bring peace between the former allies, it ultimately had no effect and he attacked her without remorse. Magneto turned his back on the X-Men for good, feeling they had not only betrayed him in not trusting his judgement, but also betraying their friendship. The X-men then assaulted the asteroid, with Cortez’ betrayal leading to Magneto’s ultimate defeat. Magneto retreated to his back-up space station Avalon where he grew even more bitter then before. Erik however soon encountered the X-men once again, during the X-Men’s siege on Avalon.
During this conflict, Magneto still held back against his former allies, until the X-Man Wolverine attacked him and almost gutted him. He then used his powers to rip the adamantium from Wolverine's skeleton, almost killing him. An angered and furious Xavier lashed out, wiping Magneto's mind and leaving him in a catatonic state. The X-man Colossus turned sides on the X-men and helped Magneto out of Avalon and returned him to a rebuild Astroid M.
Joseph
For months, the catatonic Magneto sat on his thrown on Asteroid M, being served by his Acolytes, but not being able to even utter a word. This all changed when an "Age of Apocalypse" refugee named Holocaust entered the base and brought it down around them. Magneto was saved by Colossus and found himself alone again back on earth. It was then that a mutant teleporter named Astra, as a way of revenge, restored Magneto's memories (by an unknown method) and created a clone named Joseph from his DNA. It was her plan to kill Magneto after that, but the clone went out of control and during this scene, Magneto managed to escape. For some months, it was thought that Jospeh was actually Magneto. The clone even became an ally to the X-men. It took a few more months before Magneto finally made himself known to the world once again.
Disguised as a normal human, Magneto placed the fate of humanity in the hands of an average man name William Jones. William was a building-contractor and was investigating a freakish building collapse of the Center for Humanitarian Excellence in Los Angeles, which was suspected to be the work of mutants. Magneto, posing as a board member, engaged William in conversation. The two had a pleasant conversation until Magneto showed him his powers and told him who he really was. William became afraid and told him in all honesty that he would like him to be gone from this world, not because he hated him, but because of his overwhelming power and what he did with it.
Having perverted his supposedly objective experiment in human nature to his own ends, Magneto thanked William and left him to meet his cadre of robots at the magnetic north pole, where he began to manipulate the Polar magnetic fields. Only if the United Nations would meat his demands, Magneto would stop destroying the Polar magnetic fields. Luckily, the X-men intervened and managed to defeat Magneto, with Magneto's clone Joseph dying in the process. His defeat was, however, not before the United Nations met his demands, giving Magneto his only island to rule, the nation of Genosha.
Leader of Genosha
Magneto was given full authority by the United Nation to become the leader of the Island nation of Genosha. A difficult task lay before him since the country was wrecked during the civil war between humans and mutants after the uprising of the former mutant slaves. Magneto however soon managed to establish a government and tried to bring order to the nation. Despite some difficulties, Magneto managed to pull it of. He even got help from his son and daughters, Quicksilver, Scarlet Witch and Polaris, during this time. Genosha became a utopian nation for mutants where they could live in peace and freedom. Some months later however, Magneto kidnapped Charles Xavier in order to show him what he had achieved. A newly formed team of X-men managed to free Xavier, while Wolverine gutted Magneto badly and was left with serious injuries. Magneto however had full right to defend his nation from foreign diplomacy (being the X-men) and while Magneto was defeated in battle, he won the war when the X-men left the nation.
Destruction of a Nation
Some weeks went by and Erik was healing from his last battle against the X-men. It was at this time that a full frontal Sentinel attack was undertaken on Genosha by the menace known as Cassandra Nova, who now had possession over the Sentinels, only after killing Bolivar Trask's nephew, Donald Trask and "gaining" his DNA. Magneto was seemingly one of the first to fall in battle. A giant airplane with the appearance of an iron fist entered the tower in witch Magneto was located. After this first attack, a huge Sentinel destroyed the entire city, leaving almost everyone dead in it's wake. When the X-men came to investigate they saw the slaughter of countless mutants. A true new dark age for the mutants had begun. While investigating, the X-men found a tape that was made by Magneto a few minutes prior to his seeming death. He told his nation to never give up and be strong, even in the darkest of times. It seemed that Erik Lenhsherr, Magneto, had finally perished in battle.
Xorn and Excalibur
After believing Magneto gone for good, the newest teacher at the Xavier Institute, the enigmatic, masked mutant known as Xorn, revealed himself as Magneto in disguise to Professor Xavier. This "Magneto" told Charles he had been living under their noses the whole time. He quickly defeated the X-men and, along with several mutant-students he had been teaching the last months, staged an attack on the island of Manhattan. This included murdering numerous humans in crematoriums, mirroring his Holocaust persecution. The X-Men however doubted his legitimacy as the real "Master of Magnetism". The X-men regrouped and fought Xorn. His addiction to the power-enhancing drug named “ Kick” however allowed Xorn to assault and kill Jean Grey by giving her a planetary-scale stroke. An enraged Wolverine decapitated the alleged Magneto, who was later revealed to be an impostor, actually Xorn under the influence of X-men enemy Sublime. The real Magneto had never left the island of Genosha after the attacks on it by Cassandra Nova.
Eventually, Charles Xavier contacted Magneto and went to Genosha to figure out what Erik's next move should be. He was now the world's most hated man, even though it had not been him that attacked humankind this time. Magneto was furious to think that people would actually think him able to do those horrible acts. Magneto and Xavier remained on the island for a longer period of time, in the meantime finding other survivors of the Sentinels attacks. The two became close friends once more over the period of time and Magneto finally seemed to have forsaken his more violent ways. Things all changed when Charles and Erik saw a news broadcast that showed images of Erik's daughter, Wanda Maximoff (better known as the Scarlet Witch), to have suffered a nervous breakdown and hurt and killed many of her former Avengers teammates in the process. She had been taken into custody. Magneto donned his uniform once more and went straight to New York City, leaving Charles and his more peaceful life behind.
House of M
After Wanda devastatingly, but accidentally, disbanded the Avengers and was rendered unconscious, Magneto appeared and demanded to have his daughter remanded to his care. The Avengers and the X-men at this point found out that Magneto was still alive and that he was not the one responsible for the attacks on New York City, which where actually Xorn's. The Avengers accepted a grieving father's demands and gave Wanda, somewhat reluctant, over to Magneto. Magneto then returned back with Wanda to the island of Genosha where he and Charles Xavier had spent their last months. Magneto watched over his sleeping daughter, kept unconscious by Xavier. However, both the X-men and the newly formed Avengers saw Wanda as a threat and where planing to bring Wanda in, or even have her killed should that be necessary. Magneto's son, Pietro (Quicksilver) demanded that Magneto saved her. Magneto responded that it was out of his hands and there was nothing he could do. On the one hand Wanda was indeed his flesh and blood and he would give his life for her, but on the other hand, she clearly had a mental breakdown and was dangerous.
It was then that the combined forces of the X-Men and the New Avengers arrived on Magneto's doorstep. Before they could act however, the world flashed white and when it returned, reality had been remade as a world where mutants where the dominant species and humanity was on the decline. Magneto was now ruler over the sovereign nation of Genosha, the dominant superpower in the world, and mutants held almost all worldwide positions of power.
The world has been reversed: mutants now subjugate and legislate against humans, waiting for them to die out over the natural course of their existence. When Wolverine and a mysterious girl named Layla Miller begin restoring the memories of the heroes, they staged a daring coup against Magneto’s headquarters where Wanda was kept. The revelation came out that it was actually Pietro, not Erik, who convinced Wanda to remake the world in this image. As the world crumbled around them and returned to normal reality, Wanda utters three simple words: No more mutants. When everything returns to normal, 99% of the world’s mutant population has been depowered, including Magneto. This day would be known as M-Day
The Master Returns
For the following months, Magneto wandered the Earth. He then contacted his old friend Xavier, leading them both ino trouble when Magneto's old soldiers, the Acolytes, showed up to kill Xavier. They no longer listened to Magneto, because he wasn't a mutant anymore. By teaming up, Magneto and Xavier managed to break free of the Acolytes and stop them from further pursuit. The two then went their separate ways again. Some months later, Magneto contacted the High Evolutionary, who managed to return Magneto's lost mutant powers. This all happened during a ruse where he attacked the X-Men once again. He was now the only mutant to regain his powers after losing them on M-Day.
Nation X
Magneto, with his powers back, stood for a choice, returning to his old ways or now join the X-men on their homebase known as Utopia. Since no more then 200 mutants remained after M-Day, Magneto thought the few that where still there should stand strong together. He embarked on a journey to Utopia where he was met with anger by the X-men. When he arrives, Xavier demands he leave, but Cyclops overrules him and allows Magneto to state his business. Magneto then fell down on his knees and praised Cyclops' leadership and asked him if he could join them.
Xavier refused to accept Magneto’s suspicious acts and change of heart and telepathically attacks him, but Cyclops stops the attack and orders Xavier to leave. Magneto laments the future of their race, but Cyclops assures him that Hope Summers, the Mutant Messiah is alive and well. Magneto swears fealty to the X-Men and is made a senior member of Cyclops’ cabinet. He’s still not fully accepted, however, as Cyclops reprimands him for taking what he believed to be too much initiative by constructing a giant support column to not only support Utopia, but house the Atlantean refugees, calling the structure New Atlantis.
To finally atone for his past sins, he journeys to the top of a mountain to reflect and finally realizes what he can do: bring Kitty Pryde back to Earth. He saw the massive bullet she was trapped in when he was in the High Evolutionary’s space station and uses his abilities to bring her back, but he lapses into a coma.
Return
Magneto comes out of his coma right after Hope was teleported into Utopia by a dying Nightcrawler. With the Nimrod Sentinels laying siege to Utopia, Magneto stopped Hank McCoy from leaving his patients as he stated that he had made certain promises to himself, which precluded him from laying in bed while his people were in danger of genocide. Magneto prepares for battle and manage to hold off a squad of Nimrods by attacking them with electrical blasts before finally dismembering the robots by pulling shards of iron from the core of Utopia through them. The wounded but victorious Magneto then gave a speech to the awed young mutants that surrounded him that it was their destiny to inherit the world. On one day, Magneto receives a lead from X-men teammate Dr. Nemesis on one of his old Nazi tormentors. Erik reveals to Wolverine's X-Force that he is aware of their existence, and trades his silence for the murder of the Nazi officer. Wolverine takes the task on alone and completes it.
Schism
Magneto appears alongside Emma Frost, Colossus, Namor, and Iceman at the unveiling of a mutant museum in San Francisco under orders from Cyclops. The highly publicized event is attacked by the new Hellfire Club. Each of the X-Men present are taken down one by one through technology specifically designed to defeat each of them. Magneto is shot with a miniaturized neutron star. The Hellfire Club then attaches brain slugs to the X-Men to keep them unconscious. Idie, the only mutant left in the museum unscathed, kills the remaining Hellfire members to save everyone.
The Hellfire Club unleashes a giant Sentinel, charged with destroying Utopia. Cyclops and some of the younger mutants prepare to stand their ground, while Wolverine demands that the children run and save themselves. The Sentinel winds up being defeated. However, the X-Men are split between Cyclops and Wolverine. Magneto remains loyal to Cyclops and stays on Utopia.
Regenesis
Magneto is later assigned to Cyclops' new "Extinction Team", which also consists of Namor, Danger, Magik, Colossus, Storm, Hope, and Emma Frost. In a training exercise between the Extinction Team and Hope's Lights, Magneto is attacked by Zero and reacts by brutally by ripping him in half with his magnetic powers. Zero is able to pull himself back together (which Magneto knew he was capable of doing), but Magneto is harshly reprimanded by Hope and Cyclops for attacking so harshly during a training exercise. After the apparent death of Jocasta, Hank Pym calls for Cyclops, Emma Frost and Magneto to aid him in his investigation. Upon their arrival to the West Coast Academy, Magneto agrees to assist so long as Quicksilver refrains from involving himself in any mutant affairs. He claims that Pietro coerced his sister into the events that led to her breakdown and cites his misuse of the Terrigen Mists and the war that was caused due to it.
Magneto is also faced with a ghost from his past in the form of his clone, Joseph. Disguised as Magneto, Joseph kills a group of anti-mutant protesters witch causes a conflict between Magneto and the authorities and the Avengers. The Avengers claim Magneto to be the perpetrator. However, Magneto soon found out that the mutant teleporter Astra, an old nemesis to Magneto as well as the person who created the original Joseph, was to blame for the new Joseph and the murders. Eventually Magneto managed to clear his name and defeated Astra while Joseph was brought over to Cyclops where he was imprisoned.
Avengers vs. X-Men
When Captain America arrives on Utopia to discuss Hope and the returning Phoenix Force, the two teams can not come to an agreement. This causes a rift between the two superhero teams. Where most of the X-men believe the Phoenix Force to be a force that can re-spark the dying mutant race, the Avengers believe it will cause nothing but harm. During this, Magneto stands with the X-men's Extinction Team lead by Cyclops and helps him gain the advantage during the first fight that breaks out as a result of the difference in opinion. Magneto also helps the X-men and Avengers during the following days in search of Hope and later when five of the X-men gained the Phoenix's powers.
The Mutant Revolution
Magneto helps break Cyclops out of prison and joins his group of rogue X-Men. Magneto's powers are broken due to a blast from the Phoenix Force, as well as the rest of the team's due to their exposure. With their broken abilities, the team have searched the planet for new mutants due to the re-igniting of the mutant gene. Magneto seemingly betrays the X-Men in order to work for S.H.I.E.L.D. and tell them what Cyclops' team is up to. He reveals himself to the rest of the X-Men that he did so in order to act as a double agent since the team is on the run. Magneto helps build the New Charles Xavier school from the remnants of an old Weapon X facility. He also helps in recruiting new mutants in a girl that can control time, a healer, a boy who can project golden balls, a chameleon like mutant, and even visits the Jean Grey Institute to recruit some of their students in the form of the Stepford Cuckoos, and the time-displaced Angel of the original X-Men. Magneto is now Limbo with the team to fight the threat of Dormammu and his demons. Magneto and the team hold out long enough for Magik to absorb Limbo, defeat Dormammu and cast them out back to their dimension. Scott confronts Magneto about his loyalties, but Magneto wants the end goal to be the same as Scott and the two have a conversation to further strengthen their relationship and come to terms with their standings in regards to each other. Magneto is there with the rest of the team when Emma is helping the new mutant David Bond, control his powers to show off what he can do. Magneto and the rest of the X-Men help rescue Fabio from S.H.I.E.L.D..
Magneto gets a message from Maria Hill so that they can meet up and talk. Hill tells Erik that if he wishes to continue talking with her he will have to talk to Dazzler, the new mutant liaison. Magneto ends up returning to the X-Men's hideout, where he watches a pro-mutant rally supporting Cyclops with the team. Magneto shows up late to help battle Blockbuster sentinel, and he delivers the final blow before the sentinel is called back by its master.
Magneto ponders his current situation and what his direction is. Mystique posing as Dazzler reveals herself to him and invites him to come to Madripoor. He finds that Madripoor has been made into a new safe haven for the mutants. He finds there is the drug kick being made, but he ends up meeting up with the Blob. Fred takes him to the skyscraper where Mystique is at with Sabretooth and the new Silver Samurai, where they have reformed the Brotherhood of Mutants. Erik snaps at what has happened, saying this isn't a dream but a nightmare. In his rage he attacks the team and ends up making the skyscraper collapse before riding away in a helicopter, heading off on his own.
AXIS and Time Runs Out
Magneto again appears on the scene during the events of AXIS, in which the Red Skull had taken the brain and telepathic powers of the deceased Charles Xavier, one of Erik's oldest friends. In his quest for revenge against the Red Skull, Magneto found out that Red Skull had used his new powers to wreck havok among the world and even founded his own concentration camp for mutants on the island of Genosha, Magneto's former base. As many of the heroes whom apposed the Red Skull in the initial assault fell, Magneto sought out a group of relunctant villains whom helped him fight the Red Skull. Eventually, Magneto and the rest of the heroes and villains where succesfull in taking out the Red Skull, after which Magneto took his rightfull place in Genosha, helping out the mutants that had been captured by the Skull some weeks before.
Although Magneto started rebuilding Genosha, all seemed for nothing when the Universal Incursion started happening. The multiverse had began to unravel, as each time, two planet earth's from two different universes collided, ending both universes. While many of the Marvel heroes tried to stop these incursions, Magneto also did his best in stopping the incursions. He, as well as all other heroes however failed, and the Marvel universe was seemingly destroyed forever.
Leading the X-Men
After the events of Secret Wars, reality was brought back thanks to Doctor Doom and Reed Richards. We see that Magneto is now leading a team of X-Men consisting of Psylocke, M, and Sabretooth. They are trying to find a cure for the Terrigen Mist when they discover that someone is gunning for healers. The Dark riders are their opponents, but they appear to being controlled by a unknown source.
Powers
Magnetic Field Manipulation
Magneto's mutant power gives him mastery over all forms of magnetism. He can perceive the magnetic forces of the Earth as well as the bio-electrical patterns of all living beings. He can draw on and use the magnetosphere of the planet, which extends far into space. Magneto can use his vast power to reshape even the most indestructible metals, including the adamantium in Wolverine's skeleton. He's been shown controlling the most insignificant magnetic particles in both the atmosphere and in living beings, reversing their blood flow or ripping out any ferrous elements through their tissues.
Magneto can create electromagnetic fields strong enough to manipulate non-ferrous items, though he may be using anti-gravity fields to do this. He has demonstrated the ability to lift thousands of tons with his magnetic powers, although the greater he exerts himself the greater the physical and mental stress he undergoes. Magneto has the ability to increase his physical attributes by directing his magnetic powers inward. He has been seeing increasing his physical strength and durability, as well as his speed and reaction time.
Magneto can create powerful magnetic force fields for personal protection, project blasts of electricity or magnetic energy, and generate powerful electromagnetic pulses. He can also assemble complicated machines within seconds through the use of his powers. Although Magneto's primary power is the control over magnetism, he can also manipulate any form of energy from the electromagnetic spectrum. This includes visible light, radio waves, ultraviolet light, gamma rays, and x-rays. It is more difficult for Magneto to manipulate other forms of energy, so he predominately only uses magnetism.
After his exposure to an attack from the Phoenix Force, Magneto's powers have been greatly reduced. He has shown limits in only being able to dismantle a few sentinels at a time, and has been forced to become more precise in his attacks, resulting in him using metallic objects as projectiles more frequently. Magneto has also shown he can overexert himself rather quickly, resulting in physical harm. Despite these limits, Magneto has still shown the ability to fly and use his powers in a precise and accurate manner. Recently, in a fit of rage, he made a skyscraper collapse. Perhaps this shows his powers are returning to their once former glory or that in cases of extreme emotion, his powers get stronger than their current state.
Abilities
Mental Resistance
Magneto has trained himself to defend his mind against even the strongest telepathic attacks. Due in part to his long history with Charles Xavier, he possesses a great deal of knowledge in devising technology to block psychic assaults. Magneto's helmet greatly augments his already immense mental fortitude, and even without it he has been shown resisting the intrusion of immensely powerful psychics such as Xavier and Emma Frost (whose telepathy Magneto resisted even when she possessed the Phoenix Force, though with great effort).
Genius-level Intellect
Magneto is a genius with competence in various fields of advanced science, especially genetic mutation, particle physics, engineering, and robotics. His intellect has allowed him to create many advanced and complex machines, most of which are well beyond the scope contemporary science. He has engineered advanced robots, space stations, devices capable of nullifying mutant powers except for his own, devices that generate volcanoes and earthquakes, and devices that block telepathy. He can create artificial living beings (such as Alpha the Ultimate Mutant) and fully-grown adult clones, as well as mutate humans in order to give them superhuman powers.
Master Combatant
Magneto has some military training in hand-to-combat and is capable of holding his own in a fight, though he prefers the use of his mutant powers in most combat situations. He is an able athlete despite his age, and keeps himself in excellent physical condition.
Master Tactician and Strategist
Magneto is an excellent strategist, both in actual battles and games of chess, and has extensive combat experience. He has successfully held his own in combat against entire groups of superhuman adversaries, such as the X-Men and the Avengers.
Multilingual
Magneto is a polyglot, fluent in English, German, Polish, Yiddish, French, Russian, Ukrainian, Hebrew, and Arabic. He has even managed to decipher the ancient language of a lost civilization.
Paraphernalia
Magneto's Helmet
Magneto's helmet is designed to prevent telepathic intrusion or psionic attacks. This is accomplished via technology of Magneto's own design wired into the helmet itself. The helmet has become something of a symbol, an integral part of Magneto's persona. When Magneto was thought dead after the sentinel attack on Genosha, t-shirts adorned with the image of him wearing his helmet and featuring the slogan "Magneto Was Right" started being worn by disenfranchised mutant youth as a symbol of rebellion.
The costume that Magneto wears is actually a type of armor that he has created through the use of his magnetic powers. The costume is an amalgam of various lightweight, but highly durable, metallic alloys that further protects him from many forms of physical injury.
Utility Belt
After losing most of his power due to exposure to the Phoenix Force, Magneto has resorted to donning a new outfit, including a utility belt. He has shown to keep small, metallic objects, such as nails, in his pouches to use as weapons. In times of being out of his suit, Magneto carries knives and bullets on his person.
⚡ Happy 🎯 Heroclix 💫 Friday! 👽
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A year of the shows and performers of the Bijou Planks Theater.
Secret Identity: Max Eisenhardt
Publisher: Marvel
First Appearance: The X-Men #1
(September 1963)
Created by: Stan Lee (writer)
Jack Kirby (artist)
Magneto has been in the Paprihaven story such as in issue 962, describing his view of world domination to Unger!
Evolutionary Loop 517, a monumental six-metre bronze sculpture by the London-based contemporary artist, Nasser Azam, will be unveiled on the 27th May at the University of Aberdeen. The sculpture was commissioned for the Sir Duncan Rice Library, and is a new defining landmark for the University campus. The Library was officially opened in September 2012 by Her Majesty Queen Elizabeth, and the Duke of Edinburgh.
Azam worked closely with the architect of the library, Morten Schmidt, a founding Partner of the award-winning Scandinavian architectural practice schmidt/hammer/lassen architects, who have designed some of Europe’s most ground breaking library buildings. The sculptural forms of Evolutionary Loop 517 thus establish a strong rapport with the surrounding buildings and landscape. Azam commented: “The project has been most rewarding as I was involved with the architects from the outset.Evolutionary Loop 517 to me reflects the visually striking interior design of the library and the use of bronze cements a strong connectivity between the historic relevance and traditions of the university, and the bold and beautiful statement of the contemporary library building.”
The sculpture was named following a competition launched by Aberdeen University, in collaboration with the artist. The winning entry came from Chemistry Professor Marcel Jaspars, who explained his choice: “I came up with the name as I felt this is a very organic piece, and the intertwined forms connect in a loop, which reminded me of the evolutionary process, with continuous change and connection. It reflects the fact that students, academics and staff are constantly evolving in their experiences and connections at the University of Aberdeen, to show the organic nature of the sculpture in symbiosis with the research carried out at the University and to represent the age of the University when this sculpture was made. In a diverse way, we will all have a connection with the University of Aberdeen just by looking at the sculpture. In future years, maybe people will simply say ’Let’s meet at the Loop’.”
Chris Banks, Aberdeen University Librarian and Director of Library Special Collections and Museums, commented: “I am thrilled that the sculpture is now taking pride of place in front of the library. We are extremely grateful to the donor who commissioned the piece and to Nasser who has created this stunning piece of art for us.”
The £57 million Sir Duncan Rice Library provides an advanced learning environment in which the latest learning technology adds value to a magnificent collection of over one million books and journals. It also safeguards the University’s internationally-significant archive of historic books, manuscripts and works of art within the Special Collection Centre and Loop provides another important addition to these collections. The Library is not only a magnificent and inspirational building – it is a hugely important institutional and regional asset which will benefit students, scholars and communities for decades to come.
Alongside the sculpture, Azam has finished a large painting, titled Loop, reflecting on the relationship between sculpture and architecture. Loop has entered the collection of the University, and will be hung in the new library building.
Other major commissions of Nasser Azam’s career to date include the sculpture Athena, commissioned for the entrance to London City Airport, and unveiled on 5th July 2012 to coincide with the 2012 London Olympics. Athena is the UK’s tallest bronze sculpture. Azam also created the large bronze sculpture The Dance, unveiled on the South Bank on 21 February 2008, as well as work for the National Botanic Gardens of Ireland, in Dublin.
Between 2008 and 2010 he participated in a number of high-profile ‘Performance painting’ projects including; Life In Space, a project that took place on board a Russian parabolic aircraft, where he completed two triptychs as an homage to Francis Bacon in zero gravity; and the widely reported Antarctica project, where the artist endured severe weather conditions, to create a series of large oil canvases on an ice desert of the frozen Tundra. Nasser Azam was born in Pakistan in 1963 and spent several years in Japan, before settling in London where he has a studio. He has projects coming up in New York, London and Rio de Janeiro.
NOTES TO EDITORS
Founded in 1495, the University of Aberdeen is one of the UK’s most internationally distinguished ancient universities. It has a student population of around 16,000 and a large international community of students drawn from 120 different countries. The University, which is Scotland’s third oldest, is at the forefront of teaching, learning and discovery, as it has been for over 500 years. As the ‘global university of the north’, it has consistently sent pioneers and ideas outward to every part of the world. Aberdeen is an ambitious, research-driven university with a global outlook, committed to excellence in everything it does. It is committed to providing excellent support services and facilities and has made an unprecedented multi-million pound investment to provide its students with some of the very best facilities available in the UK including the Sir Duncan Rice Library.
TIMINGS AND LOCATION OF UNVEILING
The unveiling of the sculpture will take place on 27th May will be between 11am-1pm
The address of the Library is: The Sir Duncan Rice Library, University of Aberdeen,
Rapid strata formation in soft sand (field evidence).
Photo of strata formation in soft sand on a beach, created by tidal action of the sea.
Formed in a single, high tidal event. Stunning evidence which displays multiple strata/layers.
Why this is so important ....
It has long been assumed, ever since the 17th century, that layers/strata observed in sedimentary rocks were built up gradually, layer upon layer, over many years. It certainly seemed logical at the time, from just looking at rocks, that lower layers would always be older than the layers above them, i.e. that lower layers were always laid down first followed, in time, by successive layers on top.
This was assumed to be true and became known as the superposition principle.
It was also assumed that a layer comprising a different material from a previous layer, represented a change in environmental conditions/factors.
These changes in composition of layers or strata were considered to represent different, geological eras on a global scale, spanning millions of years. This formed the basis for the Geologic Column, which is used to date rocks and also fossils. The evolutionary, 'fossil record' was based on the vast ages and assumed geological eras of the Geologic Column.
There was also circular reasoning applied with the assumed age of 'index' fossils (based on evolutionary beliefs & preconceptions) used to date strata in the Geologic Column. Dating strata from the assumed age of (index) fossils is known as Biostratigraphy.
We now know that, although these assumptions seemed logical, they are not supported by the evidence.
At the time, the mechanics of stratification were not properly known or studied.
An additional factor was that this assumed superposition and uniformitarian model became essential, with the wide acceptance of Darwinism, for the long ages required for progressive microbes-to-human evolution. There was no incentive to question or challenge the superposition, uniformitarian model, because the presumed, fossil 'record' had become dependant on it, and any change in the accepted model would present devastating implications for Darwinism.
This had the unfortunate effect of linking the study of geology so closely to Darwinism, that any study independent of Darwinian considerations was effectively stymied. This link of geology with Darwinian preconceptions is known as biostratigraphy.
Some other field evidence, in various situations, can be observed here: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
and also in the links to stunning, experimental evidence, carried out by sedimentologists, given later.
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GEOLOGIC PRINCIPLES (established by Nicholas Steno in the 17th Century):
What Nicolas Steno believed about strata formation is the basis of the principle of Superposition and the principle of Original Horizontality.
dictionary.sensagent.com/Law_of_superposition/en-en/
“Assuming that all rocks and minerals had once been fluid, Nicolas Steno reasoned that rock strata were formed when particles in a fluid such as water fell to the bottom. This process would leave horizontal layers. Thus Steno's principle of original horizontality states that rock layers form in the horizontal position, and any deviations from this horizontal position are due to the rocks being disturbed later.”)
BEDDING PLANES.
'Bedding plane' describes the surface in between each stratum which are formed during sediment deposition.
science.jrank.org/pages/6533/Strata.html
“Strata form during sediment deposition, that is, the laying down of sediment. Meanwhile, if a change in current speed or sediment grain size occurs or perhaps the sediment supply is cut off, a bedding plane forms. Bedding planes are surfaces that separate one stratum from another. Bedding planes can also form when the upper part of a sediment layer is eroded away before the next episode of deposition. Strata separated by a bedding plane may have different grain sizes, grain compositions, or colours. Sometimes these other traits are better indicators of stratification as bedding planes may be very subtle.”
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Several catastrophic events, flash floods, volcanic eruptions etc. have forced Darwinian, influenced geologists to admit to rapid stratification in some instances. However they claim it is a rare phenomenon, which they have known about for many years, and which does nothing to invalidate the Geologic Column, the fossil record, evolutionary timescale, or any of the old assumptions regarding strata formation, sedimentation and the superposition principle. They fail to face up to the fact that rapid stratification is not an extraordinary phenonemon, but rather the prevailing and normal mechanism of sedimentary deposition whenever and wherever there is moving, sediment-laden water. The experimental evidence demonstrates the mechanism and a mass of field evidence in normal (non-catastrophic) conditions shows it is a normal everyday occurrence.
It is clear from the experimental evidence that the usual process of stratification is - that strata are not formed by horizontal layers being laid on top of each other in succession, as was assumed. But by sediment being sorted in the flowing water and laid down diagonally in the direction of flow. See diagram:
www.flickr.com/photos/truth-in-science/39821536092/in/dat...
The field evidence (in the image) presented here - of rapid, simultaneous stratification refutes the Superposition Principle and the Principle of Lateral Continuity.
We now know, the Superposition Principle only applies on a rare occasion where sedimentary deposits are laid down in still water.
Superposition is required for the long evolutionary timescale, but the evidence shows it is not the general rule, as was once believed. Most sediment is laid down in moving water, where particle segregation is the general rule, resulting in the simultaneous deposition of strata/layers as shown in the photo.
See many other examples of rapid stratification (with geological features): www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Rapid, simultaneous formation of layers/strata, through particle segregation in moving water, is so easily created it has even been described by sedimentologists (working on flume experiments) as a law ...
"Upon filling the tank with water and pouring in sediments, we immediately saw what was to become the rule: The sediments sorted themselves out in very clear layers. This became so common that by the end of two weeks, we jokingly referred to Andrew's law as "It's difficult not to make layers," and Clark's law as "It's easy to make layers." Later on, I proposed the "law" that liquefaction destroys layers, as much to my surprise as that was." Ian Juby, www.ianjuby.org/sedimentation/
The field example in the photo is the result of normal, everyday tidal action formed in a single incident,
Where the water current or movement is more turbulent, violent, or catastrophic, great depths (many metres) of stratified sediment can be laid down in a short time. Certainly not the many millions of years assumed by evolutionists.
The composition of strata formed in any deposition event. is related to whatever materials are in the sediment mix, not to any particular timescale. Whatever is in the mix will be automatically sorted into strata/layers. It could be sand, or other material added from mud slides, erosion of chalk deposits, coastal erosion, volcanic ash etc. Any organic material (potential fossils), alive or dead, engulfed by, or swept into, a turbulent sediment mix, will also be sorted and buried within the rapidly, forming layers.
See many other examples of rapid stratification with geological features: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Stratified, soft sand deposit. demonstrates the rapid, stratification principle.
Important, field evidence which supports the work of the eminent, sedimentologist Dr Guy Berthault MIAS - Member of the International Association of Sedimentologists.
(Dr Berthault's experiments (www.sedimentology.fr/)
And also the experimental work of Dr M.E. Clark (Professor Emeritus, U of Illinois @ Urbana), Andrew Rodenbeck and Dr. Henry Voss, (www.ianjuby.org/sedimentation/)
Location: Yaverland, Isle of Wight. photographed 04/06/2018, formed several months earlier and in the early stages of consolidation.
This field evidence demonstrates that multiple strata in sedimentary deposits do not need millions of years to form and can be formed rapidly. This natural example confirms the principle demonstrated by the sedimentation experiments carried out by Dr Guy Berthault and other sedimentologists. It calls into question the standard, multi-million year dating of sedimentary rocks, and the dating of fossils by depth of burial or position in the strata.
Mulltiple strata/layers are evident in this example.
Dr Berthault's experiments (www.sedimentology.fr/) and other experiments (www.ianjuby.org/sedimentation/) and field studies of floods and volcanic action show that, rather than being formed by gradual, slow deposition of sucessive layers superimposed upon previous layers, with the strata or layers representing a particular timescale, particle segregation in moving water or airborne particles can form strata or layers very quickly, frequently, in a single event.
And, most importantly, lower strata are not older than upper strata, they are the same age, having been created in the same sedimentary episode.
Such field studies confirm experiments which have shown that there is no longer any reason to conclude that strata/layers in sedimentary rocks relate to different geological eras and/or a multi-million year timescale. www.youtube.com/watch?v=5PVnBaqqQw8&feature=share&.... they also show that the relative position of fossils in rocks is not indicative of an order of evolutionary succession. Obviously, the uniformitarian principle, on which the geologic column is based, can no longer be considered valid. And the multi-million, year dating of sedimentary rocks and fossils needs to be reassessed. Rapid deposition of stratified sediments also explains the enigma of polystrate fossils, i.e. large fossils that intersect several strata. In some cases, tree trunk fossils are found which intersect the strata of sedimentary rock up to forty feet in depth. upload.wikimedia.org/wikipedia/commons/thumb/0/08/Lycopsi... They must have been buried in stratified sediment in a short time (certainly not millions, thousands, or even hundreds of years), or they would have rotted away. youtu.be/vnzHU9VsliQ
In fact, the vast majority of fossils are found in good, intact condition, which is testament to their rapid burial. You don't get good fossils from gradual burial, because they would be damaged or destroyed by decay, predation or erosion. The existence of so many fossils in sedimentary rock on a global scale is stunning evidence for the rapid depostion of sedimentary rock as the general rule. It is obvious that all rock containing good intact fossils was formed from sediment laid down in a very short time, not millions, or even thousands of years.
See set of photos of other examples of rapid stratification: www.flickr.com/photos/101536517@N06/sets/72157635944904973/
Carbon dating of coal should not be possible if it is millions of years old, yet significant amounts of Carbon 14 have been detected in coal and other fossil material, which indicates that it is less than 50,000 years old. www.ldolphin.org/sewell/c14dating.html
www.grisda.org/origins/51006.htm
Evolutionists confidently cite multi-million year ages for rocks and fossils, but what most people don't realise is that no one actually knows the age of sedimentary rocks or the fossils found within them. So how are evolutionists so sure of the ages they so confidently quote? The astonishing thing is they aren't. Sedimentary rocks cannot be dated by radiometric methods*, and fossils can only be dated to less than 50,000 years with Carbon 14 dating. The method evolutionists use is based entirely on assumptions. Unbelievably, fossils are dated by the assumed age of rocks, and rocks are dated by the assumed age of fossils, that's right ... it is known as circular reasoning.
* Regarding the radiometric dating of igneous rocks, which is claimed to be relevant to the dating of sedimentary rocks, in an occasional instance there is an igneous intrusion associated with a sedimentary deposit -
Prof. Aubouin says in his Précis de Géologie: "Each radioactive element disintegrates in a characteristic and constant manner, which depends neither on the physical state (no variation with pressure or temperature or any other external constraint) nor on the chemical state (identical for an oxide or a phosphate)."
"Rocks form when magma crystallizes. Crystallisation depends on pressure and temperature, from which radioactivity is independent. So, there is no relationship between radioactivity and crystallisation.
Consequently, radioactivity doesn't date the formation of rocks. Moreover, daughter elements contained in rocks result mainly from radioactivity in magma where gravity separates the heavier parent element, from the lighter daughter element. Thus radiometric dating has no chronological signification." Dr. Guy Berthault www.sciencevsevolution.org/Berthault.htm
"A team of Russian sedimentologists directed by Alexander Lalomov (Russian Academy of Sciences’ Institute of Ore Deposits) applied paleohydraulic analyses to geological formations in Russia. One example is the publication of a report in 2007 by the Lithology and Mineral Resources journal of the Russian Academy of Sciences. It concerns the Crimean Peninsular. It shows that the time of sedimentation of the sequence studied corresponds to a virtually instantaneous episode whilst according to stratigraphy it took several millions of years. Moreover, a recent report concerning the North-West Russian plateau in the St. Petersburg region shows that the time of sedimentation was much shorter than that attributed to it by the stratigraphic time-scale: 0.05% of the time."
www.sciencevsevolution.org/Berthault.htm
Rapid strata formation and rapid erosion at Mount St Helens.
slideplayer.com/slide/5703217/18/images/28/Rapid+Strata+F...
Visit the fossil museum:
www.flickr.com/photos/101536517@N06/sets/72157641367196613/
Just how good are peer reviews of scientific papers?
www.sciencemag.org/content/342/6154/60.full
www.examiner.com/article/want-to-publish-science-paper-ju...
The neo-Darwinian idea that the human genome consists entirely of an accumulation of billions of mutations is, quite obviously, completely bonkers. Nevertheless, it is compulsorily taught in schools and universities as 'science'.
The Reconnection® is an accelerated exchange of the energy, light and information found in the Reconnective Healing Frequencies™. It is a tool to connect three systems: the lines of our planet, the meridian lines of the human body, including chakras and the universal energy grid. The Reconnection® is a once in a lifetime experience that ties us back into a timeless system of intelligence. Originally the meridian lines (sometimes called acupuncture lines) on our bodies were connected to the grid lines that encircle the planet and cross at acknowledged power places such as Machu Picchu and Sedona. These grid lines were designed to continue out and connect us to a vastly larger grid, into the entire universe.
As we reconnect and awaken to the depths of the Light that we are, we become aware of our ‘multi-dimensional’ existence and our dormant DNA is awakened. The Reconnection is about restoring yourself to spiritual wholeness and releasing or removing the blocks or interferences that have kept you separate from your intrinsic perfection.
The Reconnection takes place in two sessions, each session lasting about 45-60 minutes. You’ll lie on a massage table, shoes off, eyes closed. Sessions take place on consecutive days or with one day in-between. The Reconnection is a touch-free procedure.
Extra rest may be needed in the days following the Reconnection to allow the body to assimilate the energy change. The process of reconnecting can continue for months after the actual Reconnection takes place. As you include these frequencies into your life, your consciousness and awareness begin to shift and expand, and so do you within yourself. The Reconnection is highly recommended for people who practice any form of energy healing. Many practitioners have reported an increase in their ability to access healing energy after their Reconnection.Recognized and supported by science, Reconnective Healing® is a form of healing that facilitates us to return to an optimum state of balance by interacting with the full spectrum of frequencies that consists of energy, light and information.
These frequencies work on the whole person, therefore the work is not symptom based. Dr. Eric Pearl defines healing as, “the restoration of the person to spiritual wholeness”. This is what allows for a possible release of symptom and disease. He also points out that healing is about our evolution. It includes the evolutionary restructuring of our DNA and our reconnection to the Universe (or to God/Light/Love/ So/ Creator) on a new level.
It is recommended for persons feeling that something on the physical, mental, emotional or spiritual level is out of sync. Animals as well as humans respond very well to the Reconnective Healing experience. It is a wonderful way to honour our friends and companions of many dispositions by offering this experience to them.
Personal reconnection is the process of re-connecting the physical energy meridians person (allowing for the exchange lines) with grid lines of the planet Earth and the Cosmos. Specifically, each body has its own set of energetic lines and points that have the role of our relationship with the universe as a channel for the transmission of energy, light and information between large and small, macrocosm and microcosm, the universe and humankind.Reconnective Healing (RH) is a return to an optimal state of balance. It is the result of interacting with the fully comprehensive RH spectrum of frequencies that consists of energy, light and information. Its first basic element is energy. Energy is everything we are made up of organically, our very essence and our actual physical body. Light is the resonance and communication within these frequencies between the universe and us. The information comes through the very interaction and entrainment with the energy and the light. It’s tangible, measurable… you can actually feel it.
Reconnective Healing completely transcends traditional energy healing techniques as it allows us to let go of the concept and approach of technique itself. It is neither a therapy nor a treatment, as it does not focus on symptoms. It is something much, much more. In Reconnective Healing we do not diagnose or treat. We simply interact with the RH frequencies, bringing about healings that are often instantaneous and tend to be life long.
While science continues to explore how it works, Reconnective Healing has been confirmed and documented in more than a dozen international studies. When RH frequencies entrain with our energy body we emit and vibrate at a higher level of light. This has been shown to restructure our DNA, resulting in the emission of measurably higher levels of bio-photonic light. Stanford Professor Emeritus Dr. William Tiller says that when information carried through the Reconnective Healing frequencies is introduced, it creates coherence and order. In other words, greater harmony and balance within us.
"If you're lucky, your healing will come in the form you anticipate. If you're really lucky, your healing will come in a form
you've not even dreamed of--one which the Universe specifically has in mind for you." ~Dr. Eric Pearl
HERE
"The Reconnection is the umbrella process of reconnecting to the universe that allows for Reconnective Healing to take place. These healings and evolutionary frequencies are of a new bandwidth and are brought in via a spectrum of light and information that has never before been present on Earth. It is through
The Reconnection that we are able to interact with these new levels of light and information, and it is through these
new levels of light and information that we are able to reconnect." ~Dr. Eric Pearl
The Reconnection is about connecting our personal energy grid system, acupuncture lines and subtle anatomy, including chakras, with the energy grid system of the greater universe and the energy system of Planet Earth. When we connect with the greater universal energy grid, we receive an influx of light and information. When we connect to our planets energy grid, the circuit is complete with grounding. The full connection completely transforms our body-mind-spirit, by bringing our system to optimal balance.
Imagine your personal energy grid as a computers’ operating system. The Reconnection basically upgrades your system exponentially. Circuits fly open, new connections are made and dormant DNA is awakened as huge amounts of "new" information/light pours in. Your energy lines connect with axiatonal lines; circuits of the higher frequency grids that open the flow to higher dimensions. You are now able to receive light and information that your system was not able to receive or process before. Imagine, what that would mean for you to be fully functioning energetically?
To describe the awakenings, knowing’s, insights, aha moments, connections, or quantum leaps in knowledge that occur when you receive, or are awakened to, more Light, or to the greater being that you are, is a unique description for each individual. The Reconnection is about restoring yourself to spiritual wholeness. It's about releasing or removing the blocks or interferences that have kept you separate from your intrinsic perfection. It's about the restructuring/awakening of your DNA and your reconnection to the universe on a new level.
The Reconnection is different from Reconnective Healing. For The Reconnection, Shanell uses a “hands-off” technique and you are fully clothed. The session spans 2 days, one hour each day, in which you lay on a massage table and experience the frequencies of energy, light and information, in a way that is unique for you - sometimes you may experience pleasant physical sensations, sometimes you may see colours or symbols, you may hear sounds or you may simply enter a deep sleep for the hour. There is a higher intelligence at work during the session which supplies you with exactly the experience you need to have. The Reconnection has been known to catapult individuals on their life path, bringing clarity to life purpose and creating positive and lasting shifts.
www.healingyogini.com/reconnective-healing--the-reconnect...
Fish, any of approximately 34,000 species of vertebrate animals (phylum Chordata) found in the fresh and salt waters of the world. Living species range from the primitive jawless lampreys and hagfishes through the cartilaginous sharks, skates, and rays to the abundant and diverse bony fishes. Most fish species are cold-blooded; however, one species, the opah (Lampris guttatus), is warm-blooded.
The term fish is applied to a variety of vertebrates of several evolutionary lines. It describes a life-form rather than a taxonomic group. As members of the phylum Chordata, fish share certain features with other vertebrates. These features are gill slits at some point in the life cycle, a notochord, or skeletal supporting rod, a dorsal hollow nerve cord, and a tail. Living fishes represent some five classes, which are as distinct from one another as are the four classes of familiar air-breathing animals—amphibians, reptiles, birds, and mammals. For example, the jawless fishes (Agnatha) have gills in pouches and lack limb girdles. Extant agnathans are the lampreys and the hagfishes. As the name implies, the skeletons of fishes of the class Chondrichthyes (from chondr, “cartilage,” and ichthyes, “fish”) are made entirely of cartilage. Modern fish of this class lack a swim bladder, and their scales and teeth are made up of the same placoid material. Sharks, skates, and rays are examples of cartilaginous fishes. The bony fishes are by far the largest class. Examples range from the tiny seahorse to the 450-kg (1,000-pound) blue marlin, from the flattened soles and flounders to the boxy puffers and ocean sunfishes. Unlike the scales of the cartilaginous fishes, those of bony fishes, when present, grow throughout life and are made up of thin overlapping plates of bone. Bony fishes also have an operculum that covers the gill slits.
The study of fishes, the science of ichthyology, is of broad importance. Fishes are of interest to humans for many reasons, the most important being their relationship with and dependence on the environment. A more obvious reason for interest in fishes is their role as a moderate but important part of the world’s food supply. This resource, once thought unlimited, is now realized to be finite and in delicate balance with the biological, chemical, and physical factors of the aquatic environment. Overfishing, pollution, and alteration of the environment are the chief enemies of proper fisheries management, both in fresh waters and in the ocean. (For a detailed discussion of the technology and economics of fisheries, see commercial fishing.) Another practical reason for studying fishes is their use in disease control. As predators on mosquito larvae, they help curb malaria and other mosquito-borne diseases.
Fishes are valuable laboratory animals in many aspects of medical and biological research. For example, the readiness of many fishes to acclimate to captivity has allowed biologists to study behaviour, physiology, and even ecology under relatively natural conditions. Fishes have been especially important in the study of animal behaviour, where research on fishes has provided a broad base for the understanding of the more flexible behaviour of the higher vertebrates. The zebra fish is used as a model in studies of gene expression.
There are aesthetic and recreational reasons for an interest in fishes. Millions of people keep live fishes in home aquariums for the simple pleasure of observing the beauty and behaviour of animals otherwise unfamiliar to them. Aquarium fishes provide a personal challenge to many aquarists, allowing them to test their ability to keep a small section of the natural environment in their homes. Sportfishing is another way of enjoying the natural environment, also indulged in by millions of people every year. Interest in aquarium fishes and sportfishing supports multimillion-dollar industries throughout the world.
Fishes have been in existence for more than 450 million years, during which time they have evolved repeatedly to fit into almost every conceivable type of aquatic habitat. In a sense, land vertebrates are simply highly modified fishes: when fishes colonized the land habitat, they became tetrapod (four-legged) land vertebrates. The popular conception of a fish as a slippery, streamlined aquatic animal that possesses fins and breathes by gills applies to many fishes, but far more fishes deviate from that conception than conform to it. For example, the body is elongate in many forms and greatly shortened in others; the body is flattened in some (principally in bottom-dwelling fishes) and laterally compressed in many others; the fins may be elaborately extended, forming intricate shapes, or they may be reduced or even lost; and the positions of the mouth, eyes, nostrils, and gill openings vary widely. Air breathers have appeared in several evolutionary lines.
Many fishes are cryptically coloured and shaped, closely matching their respective environments; others are among the most brilliantly coloured of all organisms, with a wide range of hues, often of striking intensity, on a single individual. The brilliance of pigments may be enhanced by the surface structure of the fish, so that it almost seems to glow. A number of unrelated fishes have actual light-producing organs. Many fishes are able to alter their coloration—some for the purpose of camouflage, others for the enhancement of behavioral signals.
Fishes range in adult length from less than 10 mm (0.4 inch) to more than 20 metres (60 feet) and in weight from about 1.5 grams (less than 0.06 ounce) to many thousands of kilograms. Some live in shallow thermal springs at temperatures slightly above 42 °C (100 °F), others in cold Arctic seas a few degrees below 0 °C (32 °F) or in cold deep waters more than 4,000 metres (13,100 feet) beneath the ocean surface. The structural and, especially, the physiological adaptations for life at such extremes are relatively poorly known and provide the scientifically curious with great incentive for study.
Almost all natural bodies of water bear fish life, the exceptions being very hot thermal ponds and extremely salt-alkaline lakes, such as the Dead Sea in Asia and the Great Salt Lake in North America. The present distribution of fishes is a result of the geological history and development of Earth as well as the ability of fishes to undergo evolutionary change and to adapt to the available habitats. Fishes may be seen to be distributed according to habitat and according to geographical area. Major habitat differences are marine and freshwater. For the most part, the fishes in a marine habitat differ from those in a freshwater habitat, even in adjacent areas, but some, such as the salmon, migrate from one to the other. The freshwater habitats may be seen to be of many kinds. Fishes found in mountain torrents, Arctic lakes, tropical lakes, temperate streams, and tropical rivers will all differ from each other, both in obvious gross structure and in physiological attributes. Even in closely adjacent habitats where, for example, a tropical mountain torrent enters a lowland stream, the fish fauna will differ. The marine habitats can be divided into deep ocean floors (benthic), mid-water oceanic (bathypelagic), surface oceanic (pelagic), rocky coast, sandy coast, muddy shores, bays, estuaries, and others. Also, for example, rocky coastal shores in tropical and temperate regions will have different fish faunas, even when such habitats occur along the same coastline.
Although much is known about the present geographical distribution of fishes, far less is known about how that distribution came about. Many parts of the fish fauna of the fresh waters of North America and Eurasia are related and undoubtedly have a common origin. The faunas of Africa and South America are related, extremely old, and probably an expression of the drifting apart of the two continents. The fauna of southern Asia is related to that of Central Asia, and some of it appears to have entered Africa. The extremely large shore-fish faunas of the Indian and tropical Pacific oceans comprise a related complex, but the tropical shore fauna of the Atlantic, although containing Indo-Pacific components, is relatively limited and probably younger. The Arctic and Antarctic marine faunas are quite different from each other. The shore fauna of the North Pacific is quite distinct, and that of the North Atlantic more limited and probably younger. Pelagic oceanic fishes, especially those in deep waters, are similar the world over, showing little geographical isolation in terms of family groups. The deep oceanic habitat is very much the same throughout the world, but species differences do exist, showing geographical areas determined by oceanic currents and water masses.
All aspects of the life of a fish are closely correlated with adaptation to the total environment, physical, chemical, and biological. In studies, all the interdependent aspects of fish, such as behaviour, locomotion, reproduction, and physical and physiological characteristics, must be taken into account.
Correlated with their adaptation to an extremely wide variety of habitats is the extremely wide variety of life cycles that fishes display. The great majority hatch from relatively small eggs a few days to several weeks or more after the eggs are scattered in the water. Newly hatched young are still partially undeveloped and are called larvae until body structures such as fins, skeleton, and some organs are fully formed. Larval life is often very short, usually less than a few weeks, but it can be very long, some lampreys continuing as larvae for at least five years. Young and larval fishes, before reaching sexual maturity, must grow considerably, and their small size and other factors often dictate that they live in a habitat different than that of the adults. For example, most tropical marine shore fishes have pelagic larvae. Larval food also is different, and larval fishes often live in shallow waters, where they may be less exposed to predators.
After a fish reaches adult size, the length of its life is subject to many factors, such as innate rates of aging, predation pressure, and the nature of the local climate. The longevity of a species in the protected environment of an aquarium may have nothing to do with how long members of that species live in the wild. Many small fishes live only one to three years at the most. In some species, however, individuals may live as long as 10 or 20 or even 100 years.
Fish behaviour is a complicated and varied subject. As in almost all animals with a central nervous system, the nature of a response of an individual fish to stimuli from its environment depends upon the inherited characteristics of its nervous system, on what it has learned from past experience, and on the nature of the stimuli. Compared with the variety of human responses, however, that of a fish is stereotyped, not subject to much modification by “thought” or learning, and investigators must guard against anthropomorphic interpretations of fish behaviour.
Fishes perceive the world around them by the usual senses of sight, smell, hearing, touch, and taste and by special lateral line water-current detectors. In the few fishes that generate electric fields, a process that might best be called electrolocation aids in perception. One or another of these senses often is emphasized at the expense of others, depending upon the fish’s other adaptations. In fishes with large eyes, the sense of smell may be reduced; others, with small eyes, hunt and feed primarily by smell (such as some eels).
Specialized behaviour is primarily concerned with the three most important activities in the fish’s life: feeding, reproduction, and escape from enemies. Schooling behaviour of sardines on the high seas, for instance, is largely a protective device to avoid enemies, but it is also associated with and modified by their breeding and feeding requirements. Predatory fishes are often solitary, lying in wait to dart suddenly after their prey, a kind of locomotion impossible for beaked parrot fishes, which feed on coral, swimming in small groups from one coral head to the next. In addition, some predatory fishes that inhabit pelagic environments, such as tunas, often school.
Sleep in fishes, all of which lack true eyelids, consists of a seemingly listless state in which the fish maintains its balance but moves slowly. If attacked or disturbed, most can dart away. A few kinds of fishes lie on the bottom to sleep. Most catfishes, some loaches, and some eels and electric fishes are strictly nocturnal, being active and hunting for food during the night and retiring during the day to holes, thick vegetation, or other protective parts of the environment.
Communication between members of a species or between members of two or more species often is extremely important, especially in breeding behaviour (see below Reproduction). The mode of communication may be visual, as between the small so-called cleaner fish and a large fish of a very different species. The larger fish often allows the cleaner to enter its mouth to remove gill parasites. The cleaner is recognized by its distinctive colour and actions and therefore is not eaten, even if the larger fish is normally a predator. Communication is often chemical, signals being sent by specific chemicals called pheromones.
Many fishes have a streamlined body and swim freely in open water. Fish locomotion is closely correlated with habitat and ecological niche (the general position of the animal to its environment).
Many fishes in both marine and fresh waters swim at the surface and have mouths adapted to feed best (and sometimes only) at the surface. Often such fishes are long and slender, able to dart at surface insects or at other surface fishes and in turn to dart away from predators; needlefishes, halfbeaks, and topminnows (such as killifish and mosquito fish) are good examples. Oceanic flying fishes escape their predators by gathering speed above the water surface, with the lower lobe of the tail providing thrust in the water. They then glide hundreds of yards on enlarged, winglike pectoral and pelvic fins. South American freshwater flying fishes escape their enemies by jumping and propelling their strongly keeled bodies out of the water.
So-called mid-water swimmers, the most common type of fish, are of many kinds and live in many habitats. The powerful fusiform tunas and the trouts, for example, are adapted for strong, fast swimming, the tunas to capture prey speedily in the open ocean and the trouts to cope with the swift currents of streams and rivers. The trout body form is well adapted to many habitats. Fishes that live in relatively quiet waters such as bays or lake shores or slow rivers usually are not strong, fast swimmers but are capable of short, quick bursts of speed to escape a predator. Many of these fishes have their sides flattened, examples being the sunfish and the freshwater angelfish of aquarists. Fish associated with the bottom or substrate usually are slow swimmers. Open-water plankton-feeding fishes almost always remain fusiform and are capable of rapid, strong movement (for example, sardines and herrings of the open ocean and also many small minnows of streams and lakes).
Bottom-living fishes are of many kinds and have undergone many types of modification of their body shape and swimming habits. Rays, which evolved from strong-swimming mid-water sharks, usually stay close to the bottom and move by undulating their large pectoral fins. Flounders live in a similar habitat and move over the bottom by undulating the entire body. Many bottom fishes dart from place to place, resting on the bottom between movements, a motion common in gobies. One goby relative, the mudskipper, has taken to living at the edge of pools along the shore of muddy mangrove swamps. It escapes its enemies by flipping rapidly over the mud, out of the water. Some catfishes, synbranchid eels, the so-called climbing perch, and a few other fishes venture out over damp ground to find more promising waters than those that they left. They move by wriggling their bodies, sometimes using strong pectoral fins; most have accessory air-breathing organs. Many bottom-dwelling fishes live in mud holes or rocky crevices. Marine eels and gobies commonly are found in such habitats and for the most part venture far beyond their cavelike homes. Some bottom dwellers, such as the clingfishes (Gobiesocidae), have developed powerful adhesive disks that enable them to remain in place on the substrate in areas such as rocky coasts, where the action of the waves is great.
The methods of reproduction in fishes are varied, but most fishes lay a large number of small eggs, fertilized and scattered outside of the body. The eggs of pelagic fishes usually remain suspended in the open water. Many shore and freshwater fishes lay eggs on the bottom or among plants. Some have adhesive eggs. The mortality of the young and especially of the eggs is very high, and often only a few individuals grow to maturity out of hundreds, thousands, and in some cases millions of eggs laid.
Males produce sperm, usually as a milky white substance called milt, in two (sometimes one) testes within the body cavity. In bony fishes a sperm duct leads from each testis to a urogenital opening behind the vent or anus. In sharks and rays and in cyclostomes the duct leads to a cloaca. Sometimes the pelvic fins are modified to help transmit the milt to the eggs at the female’s vent or on the substrate where the female has placed them. Sometimes accessory organs are used to fertilize females internally—for example, the claspers of many sharks and rays.
In the females the eggs are formed in two ovaries (sometimes only one) and pass through the ovaries to the urogenital opening and to the outside. In some fishes the eggs are fertilized internally but are shed before development takes place. Members of about a dozen families each of bony fishes (teleosts) and sharks bear live young. Many skates and rays also bear live young. In some bony fishes the eggs simply develop within the female, the young emerging when the eggs hatch (ovoviviparous). Others develop within the ovary and are nourished by ovarian tissues after hatching (viviparous). There are also other methods utilized by fishes to nourish young within the female. In all live-bearers the young are born at a relatively large size and are few in number. In one family of primarily marine fishes, the surfperches from the Pacific coast of North America, Japan, and Korea, the males of at least one species are born sexually mature, although they are not fully grown.
Some fishes are hermaphroditic—an individual producing both sperm and eggs, usually at different stages of its life. Self-fertilization, however, is probably rare.
Successful reproduction and, in many cases, defense of the eggs and the young are assured by rather stereotypical but often elaborate courtship and parental behaviour, either by the male or the female or both. Some fishes prepare nests by hollowing out depressions in the sand bottom (cichlids, for example), build nests with plant materials and sticky threads excreted by the kidneys (sticklebacks), or blow a cluster of mucus-covered bubbles at the water surface (gouramis). The eggs are laid in these structures. Some varieties of cichlids and catfishes incubate eggs in their mouths.
Some fishes, such as salmon, undergo long migrations from the ocean and up large rivers to spawn in the gravel beds where they themselves hatched (anadromous fishes). Some, such as the freshwater eels (family Anguillidae), live and grow to maturity in fresh water and migrate to the sea to spawn (catadromous fishes). Other fishes undertake shorter migrations from lakes into streams, within the ocean, or enter spawning habitats that they do not ordinarily occupy in other ways.
The basic structure and function of the fish body are similar to those of all other vertebrates. The usual four types of tissues are present: surface or epithelial, connective (bone, cartilage, and fibrous tissues, as well as their derivative, blood), nerve, and muscle tissues. In addition, the fish’s organs and organ systems parallel those of other vertebrates.
The typical fish body is streamlined and spindle-shaped, with an anterior head, a gill apparatus, and a heart, the latter lying in the midline just below the gill chamber. The body cavity, containing the vital organs, is situated behind the head in the lower anterior part of the body. The anus usually marks the posterior termination of the body cavity and most often occurs just in front of the base of the anal fin. The spinal cord and vertebral column continue from the posterior part of the head to the base of the tail fin, passing dorsal to the body cavity and through the caudal (tail) region behind the body cavity. Most of the body is of muscular tissue, a high proportion of which is necessitated by swimming. In the course of evolution this basic body plan has been modified repeatedly into the many varieties of fish shapes that exist today.
The skeleton forms an integral part of the fish’s locomotion system, as well as serving to protect vital parts. The internal skeleton consists of the skull bones (except for the roofing bones of the head, which are really part of the external skeleton), the vertebral column, and the fin supports (fin rays). The fin supports are derived from the external skeleton but will be treated here because of their close functional relationship to the internal skeleton. The internal skeleton of cyclostomes, sharks, and rays is of cartilage; that of many fossil groups and some primitive living fishes is mostly of cartilage but may include some bone. In place of the vertebral column, the earliest vertebrates had a fully developed notochord, a flexible stiff rod of viscous cells surrounded by a strong fibrous sheath. During the evolution of modern fishes the rod was replaced in part by cartilage and then by ossified cartilage. Sharks and rays retain a cartilaginous vertebral column; bony fishes have spool-shaped vertebrae that in the more primitive living forms only partially replace the notochord. The skull, including the gill arches and jaws of bony fishes, is fully, or at least partially, ossified. That of sharks and rays remains cartilaginous, at times partially replaced by calcium deposits but never by true bone.
The supportive elements of the fins (basal or radial bones or both) have changed greatly during fish evolution. Some of these changes are described in the section below (Evolution and paleontology). Most fishes possess a single dorsal fin on the midline of the back. Many have two and a few have three dorsal fins. The other fins are the single tail and anal fins and paired pelvic and pectoral fins. A small fin, the adipose fin, with hairlike fin rays, occurs in many of the relatively primitive teleosts (such as trout) on the back near the base of the caudal fin.
The skin of a fish must serve many functions. It aids in maintaining the osmotic balance, provides physical protection for the body, is the site of coloration, contains sensory receptors, and, in some fishes, functions in respiration. Mucous glands, which aid in maintaining the water balance and offer protection from bacteria, are extremely numerous in fish skin, especially in cyclostomes and teleosts. Since mucous glands are present in the modern lampreys, it is reasonable to assume that they were present in primitive fishes, such as the ancient Silurian and Devonian agnathans. Protection from abrasion and predation is another function of the fish skin, and dermal (skin) bone arose early in fish evolution in response to this need. It is thought that bone first evolved in skin and only later invaded the cartilaginous areas of the fish’s body, to provide additional support and protection. There is some argument as to which came first, cartilage or bone, and fossil evidence does not settle the question. In any event, dermal bone has played an important part in fish evolution and has different characteristics in different groups of fishes. Several groups are characterized at least in part by the kind of bony scales they possess.
Scales have played an important part in the evolution of fishes. Primitive fishes usually had thick bony plates or thick scales in several layers of bone, enamel, and related substances. Modern teleost fishes have scales of bone, which, while still protective, allow much more freedom of motion in the body. A few modern teleosts (some catfishes, sticklebacks, and others) have secondarily acquired bony plates in the skin. Modern and early sharks possessed placoid scales, a relatively primitive type of scale with a toothlike structure, consisting of an outside layer of enamel-like substance (vitrodentine), an inner layer of dentine, and a pulp cavity containing nerves and blood vessels. Primitive bony fishes had thick scales of either the ganoid or the cosmoid type. Cosmoid scales have a hard, enamel-like outer layer, an inner layer of cosmine (a form of dentine), and then a layer of vascular bone (isopedine). In ganoid scales the hard outer layer is different chemically and is called ganoin. Under this is a cosminelike layer and then a vascular bony layer. The thin, translucent bony scales of modern fishes, called cycloid and ctenoid (the latter distinguished by serrations at the edges), lack enameloid and dentine layers.
Skin has several other functions in fishes. It is well supplied with nerve endings and presumably receives tactile, thermal, and pain stimuli. Skin is also well supplied with blood vessels. Some fishes breathe in part through the skin, by the exchange of oxygen and carbon dioxide between the surrounding water and numerous small blood vessels near the skin surface.
Skin serves as protection through the control of coloration. Fishes exhibit an almost limitless range of colours. The colours often blend closely with the surroundings, effectively hiding the animal. Many fishes use bright colours for territorial advertisement or as recognition marks for other members of their own species, or sometimes for members of other species. Many fishes can change their colour to a greater or lesser degree, by movement of pigment within the pigment cells (chromatophores). Black pigment cells (melanophores), of almost universal occurrence in fishes, are often juxtaposed with other pigment cells. When placed beneath iridocytes or leucophores (bearing the silvery or white pigment guanine), melanophores produce structural colours of blue and green. These colours are often extremely intense, because they are formed by refraction of light through the needlelike crystals of guanine. The blue and green refracted colours are often relatively pure, lacking the red and yellow rays, which have been absorbed by the black pigment (melanin) of the melanophores. Yellow, orange, and red colours are produced by erythrophores, cells containing the appropriate carotenoid pigments. Other colours are produced by combinations of melanophores, erythrophores, and iridocytes.
The major portion of the body of most fishes consists of muscles. Most of the mass is trunk musculature, the fin muscles usually being relatively small. The caudal fin is usually the most powerful fin, being moved by the trunk musculature. The body musculature is usually arranged in rows of chevron-shaped segments on each side. Contractions of these segments, each attached to adjacent vertebrae and vertebral processes, bends the body on the vertebral joint, producing successive undulations of the body, passing from the head to the tail, and producing driving strokes of the tail. It is the latter that provides the strong forward movement for most fishes.
The digestive system, in a functional sense, starts at the mouth, with the teeth used to capture prey or collect plant foods. Mouth shape and tooth structure vary greatly in fishes, depending on the kind of food normally eaten. Most fishes are predacious, feeding on small invertebrates or other fishes and have simple conical teeth on the jaws, on at least some of the bones of the roof of the mouth, and on special gill arch structures just in front of the esophagus. The latter are throat teeth. Most predacious fishes swallow their prey whole, and the teeth are used for grasping and holding prey, for orienting prey to be swallowed (head first) and for working the prey toward the esophagus. There are a variety of tooth types in fishes. Some fishes, such as sharks and piranhas, have cutting teeth for biting chunks out of their victims. A shark’s tooth, although superficially like that of a piranha, appears in many respects to be a modified scale, while that of the piranha is like that of other bony fishes, consisting of dentine and enamel. Parrot fishes have beaklike mouths with short incisor-like teeth for breaking off coral and have heavy pavementlike throat teeth for crushing the coral. Some catfishes have small brushlike teeth, arranged in rows on the jaws, for scraping plant and animal growth from rocks. Many fishes (such as the Cyprinidae or minnows) have no jaw teeth at all but have very strong throat teeth.
Some fishes gather planktonic food by straining it from their gill cavities with numerous elongate stiff rods (gill rakers) anchored by one end to the gill bars. The food collected on these rods is passed to the throat, where it is swallowed. Most fishes have only short gill rakers that help keep food particles from escaping out the mouth cavity into the gill chamber.
Once reaching the throat, food enters a short, often greatly distensible esophagus, a simple tube with a muscular wall leading into a stomach. The stomach varies greatly in fishes, depending upon the diet. In most predacious fishes it is a simple straight or curved tube or pouch with a muscular wall and a glandular lining. Food is largely digested there and leaves the stomach in liquid form.
Between the stomach and the intestine, ducts enter the digestive tube from the liver and pancreas. The liver is a large, clearly defined organ. The pancreas may be embedded in it, diffused through it, or broken into small parts spread along some of the intestine. The junction between the stomach and the intestine is marked by a muscular valve. Pyloric ceca (blind sacs) occur in some fishes at this junction and have a digestive or absorptive function or both.
The intestine itself is quite variable in length, depending upon the fish’s diet. It is short in predacious forms, sometimes no longer than the body cavity, but long in herbivorous forms, being coiled and several times longer than the entire length of the fish in some species of South American catfishes. The intestine is primarily an organ for absorbing nutrients into the bloodstream. The larger its internal surface, the greater its absorptive efficiency, and a spiral valve is one method of increasing its absorption surface.
Sharks, rays, chimaeras, lungfishes, surviving chondrosteans, holosteans, and even a few of the more primitive teleosts have a spiral valve or at least traces of it in the intestine. Most modern teleosts have increased the area of the intestinal walls by having numerous folds and villi (fingerlike projections) somewhat like those in humans. Undigested substances are passed to the exterior through the anus in most teleost fishes. In lungfishes, sharks, and rays, it is first passed through the cloaca, a common cavity receiving the intestinal opening and the ducts from the urogenital system.
Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills. The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour. Water taken in continuously through the mouth passes backward between the gill bars and over the gill filaments, where the exchange of gases takes place. The gills are protected by a gill cover in teleosts and many other fishes but by flaps of skin in sharks, rays, and some of the older fossil fish groups. The blood capillaries in the gill filaments are close to the gill surface to take up oxygen from the water and to give up excess carbon dioxide to the water.
Most modern fishes have a hydrostatic (ballast) organ, called the swim bladder, that lies in the body cavity just below the kidney and above the stomach and intestine. It originated as a diverticulum of the digestive canal. In advanced teleosts, especially the acanthopterygians, the bladder has lost its connection with the digestive tract, a condition called physoclistic. The connection has been retained (physostomous) by many relatively primitive teleosts. In several unrelated lines of fishes, the bladder has become specialized as a lung or, at least, as a highly vascularized accessory breathing organ. Some fishes with such accessory organs are obligate air breathers and will drown if denied access to the surface, even in well-oxygenated water. Fishes with a hydrostatic form of swim bladder can control their depth by regulating the amount of gas in the bladder. The gas, mostly oxygen, is secreted into the bladder by special glands, rendering the fish more buoyant; the gas is absorbed into the bloodstream by another special organ, reducing the overall buoyancy and allowing the fish to sink. Some deep-sea fishes may have oils, rather than gas, in the bladder. Other deep-sea and some bottom-living forms have much-reduced swim bladders or have lost the organ entirely.
The swim bladder of fishes follows the same developmental pattern as the lungs of land vertebrates. There is no doubt that the two structures have the same historical origin in primitive fishes. More or less intermediate forms still survive among the more primitive types of fishes, such as the lungfishes Lepidosiren and Protopterus.
The circulatory, or blood vascular, system consists of the heart, the arteries, the capillaries, and the veins. It is in the capillaries that the interchange of oxygen, carbon dioxide, nutrients, and other substances such as hormones and waste products takes place. The capillaries lead to the veins, which return the venous blood with its waste products to the heart, kidneys, and gills. There are two kinds of capillary beds: those in the gills and those in the rest of the body. The heart, a folded continuous muscular tube with three or four saclike enlargements, undergoes rhythmic contractions and receives venous blood in a sinus venosus. It passes the blood to an auricle and then into a thick muscular pump, the ventricle. From the ventricle the blood goes to a bulbous structure at the base of a ventral aorta just below the gills. The blood passes to the afferent (receiving) arteries of the gill arches and then to the gill capillaries. There waste gases are given off to the environment, and oxygen is absorbed. The oxygenated blood enters efferent (exuant) arteries of the gill arches and then flows into the dorsal aorta. From there blood is distributed to the tissues and organs of the body. One-way valves prevent backflow. The circulation of fishes thus differs from that of the reptiles, birds, and mammals in that oxygenated blood is not returned to the heart prior to distribution to the other parts of the body.
The primary excretory organ in fishes, as in other vertebrates, is the kidney. In fishes some excretion also takes place in the digestive tract, skin, and especially the gills (where ammonia is given off). Compared with land vertebrates, fishes have a special problem in maintaining their internal environment at a constant concentration of water and dissolved substances, such as salts. Proper balance of the internal environment (homeostasis) of a fish is in a great part maintained by the excretory system, especially the kidney.
The kidney, gills, and skin play an important role in maintaining a fish’s internal environment and checking the effects of osmosis. Marine fishes live in an environment in which the water around them has a greater concentration of salts than they can have inside their body and still maintain life. Freshwater fishes, on the other hand, live in water with a much lower concentration of salts than they require inside their bodies. Osmosis tends to promote the loss of water from the body of a marine fish and absorption of water by that of a freshwater fish. Mucus in the skin tends to slow the process but is not a sufficient barrier to prevent the movement of fluids through the permeable skin. When solutions on two sides of a permeable membrane have different concentrations of dissolved substances, water will pass through the membrane into the more concentrated solution, while the dissolved chemicals move into the area of lower concentration (diffusion).
The kidney of freshwater fishes is often larger in relation to body weight than that of marine fishes. In both groups the kidney excretes wastes from the body, but the kidney of freshwater fishes also excretes large amounts of water, counteracting the water absorbed through the skin. Freshwater fishes tend to lose salt to the environment and must replace it. They get some salt from their food, but the gills and skin inside the mouth actively absorb salt from water passed through the mouth. This absorption is performed by special cells capable of moving salts against the diffusion gradient. Freshwater fishes drink very little water and take in little water with their food.
Marine fishes must conserve water, and therefore their kidneys excrete little water. To maintain their water balance, marine fishes drink large quantities of seawater, retaining most of the water and excreting the salt. Most nitrogenous waste in marine fishes appears to be secreted by the gills as ammonia. Marine fishes can excrete salt by clusters of special cells (chloride cells) in the gills.
There are several teleosts—for example, the salmon—that travel between fresh water and seawater and must adjust to the reversal of osmotic gradients. They adjust their physiological processes by spending time (often surprisingly little time) in the intermediate brackish environment.
Marine hagfishes, sharks, and rays have osmotic concentrations in their blood about equal to that of seawater and so do not have to drink water nor perform much physiological work to maintain their osmotic balance. In sharks and rays the osmotic concentration is kept high by retention of urea in the blood. Freshwater sharks have a lowered concentration of urea in the blood.
Endocrine glands secrete their products into the bloodstream and body tissues and, along with the central nervous system, control and regulate many kinds of body functions. Cyclostomes have a well-developed endocrine system, and presumably it was well developed in the early Agnatha, ancestral to modern fishes. Although the endocrine system in fishes is similar to that of higher vertebrates, there are numerous differences in detail. The pituitary, the thyroid, the suprarenals, the adrenals, the pancreatic islets, the sex glands (ovaries and testes), the inner wall of the intestine, and the bodies of the ultimobranchial gland make up the endocrine system in fishes. There are some others whose function is not well understood. These organs regulate sexual activity and reproduction, growth, osmotic pressure, general metabolic activities such as the storage of fat and the utilization of foodstuffs, blood pressure, and certain aspects of skin colour. Many of these activities are also controlled in part by the central nervous system, which works with the endocrine system in maintaining the life of a fish. Some parts of the endocrine system are developmentally, and undoubtedly evolutionarily, derived from the nervous system.
As in all vertebrates, the nervous system of fishes is the primary mechanism coordinating body activities, as well as integrating these activities in the appropriate manner with stimuli from the environment. The central nervous system, consisting of the brain and spinal cord, is the primary integrating mechanism. The peripheral nervous system, consisting of nerves that connect the brain and spinal cord to various body organs, carries sensory information from special receptor organs such as the eyes, internal ears, nares (sense of smell), taste glands, and others to the integrating centres of the brain and spinal cord. The peripheral nervous system also carries information via different nerve cells from the integrating centres of the brain and spinal cord. This coded information is carried to the various organs and body systems, such as the skeletal muscular system, for appropriate action in response to the original external or internal stimulus. Another branch of the nervous system, the autonomic nervous system, helps to coordinate the activities of many glands and organs and is itself closely connected to the integrating centres of the brain.
The brain of the fish is divided into several anatomical and functional parts, all closely interconnected but each serving as the primary centre of integrating particular kinds of responses and activities. Several of these centres or parts are primarily associated with one type of sensory perception, such as sight, hearing, or smell (olfaction).
The sense of smell is important in almost all fishes. Certain eels with tiny eyes depend mostly on smell for location of food. The olfactory, or nasal, organ of fishes is located on the dorsal surface of the snout. The lining of the nasal organ has special sensory cells that perceive chemicals dissolved in the water, such as substances from food material, and send sensory information to the brain by way of the first cranial nerve. Odour also serves as an alarm system. Many fishes, especially various species of freshwater minnows, react with alarm to a chemical released from the skin of an injured member of their own species.
Many fishes have a well-developed sense of taste, and tiny pitlike taste buds or organs are located not only within their mouth cavities but also over their heads and parts of their body. Catfishes, which often have poor vision, have barbels (“whiskers”) that serve as supplementary taste organs, those around the mouth being actively used to search out food on the bottom. Some species of naturally blind cave fishes are especially well supplied with taste buds, which often cover most of their body surface.
Sight is extremely important in most fishes. The eye of a fish is basically like that of all other vertebrates, but the eyes of fishes are extremely varied in structure and adaptation. In general, fishes living in dark and dim water habitats have large eyes, unless they have specialized in some compensatory way so that another sense (such as smell) is dominant, in which case the eyes will often be reduced. Fishes living in brightly lighted shallow waters often will have relatively small but efficient eyes. Cyclostomes have somewhat less elaborate eyes than other fishes, with skin stretched over the eyeball perhaps making their vision somewhat less effective. Most fishes have a spherical lens and accommodate their vision to far or near subjects by moving the lens within the eyeball. A few sharks accommodate by changing the shape of the lens, as in land vertebrates. Those fishes that are heavily dependent upon the eyes have especially strong muscles for accommodation. Most fishes see well, despite the restrictions imposed by frequent turbidity of the water and by light refraction.
Fossil evidence suggests that colour vision evolved in fishes more than 300 million years ago, but not all living fishes have retained this ability. Experimental evidence indicates that many shallow-water fishes, if not all, have colour vision and see some colours especially well, but some bottom-dwelling shore fishes live in areas where the water is sufficiently deep to filter out most if not all colours, and these fishes apparently never see colours. When tested in shallow water, they apparently are unable to respond to colour differences.
Sound perception and balance are intimately associated senses in a fish. The organs of hearing are entirely internal, located within the skull, on each side of the brain and somewhat behind the eyes. Sound waves, especially those of low frequencies, travel readily through water and impinge directly upon the bones and fluids of the head and body, to be transmitted to the hearing organs. Fishes readily respond to sound; for example, a trout conditioned to escape by the approach of fishermen will take flight upon perceiving footsteps on a stream bank even if it cannot see a fisherman. Compared with humans, however, the range of sound frequencies heard by fishes is greatly restricted. Many fishes communicate with each other by producing sounds in their swim bladders, in their throats by rasping their teeth, and in other ways.
A fish or other vertebrate seldom has to rely on a single type of sensory information to determine the nature of the environment around it. A catfish uses taste and touch when examining a food object with its oral barbels. Like most other animals, fishes have many touch receptors over their body surface. Pain and temperature receptors also are present in fishes and presumably produce the same kind of information to a fish as to humans. Fishes react in a negative fashion to stimuli that would be painful to human beings, suggesting that they feel a sensation of pain.
An important sensory system in fishes that is absent in other vertebrates (except some amphibians) is the lateral line system. This consists of a series of heavily innervated small canals located in the skin and bone around the eyes, along the lower jaw, over the head, and down the mid-side of the body, where it is associated with the scales. Intermittently along these canals are located tiny sensory organs (pit organs) that apparently detect changes in pressure. The system allows a fish to sense changes in water currents and pressure, thereby helping the fish to orient itself to the various changes that occur in the physical environment.
Evolutionary high jinks for all the family in the grounds of Down House, Charles Darwin's home for the 40 years until his death in 1882. It was in this house that he did much of his experimental work, formulated his ideas and wrote his books. It's a marvellous place to visit, with beautiful grounds as well.
A year ago today I was wearing borrowed shoes.
Such an evolutionary jump from the F360 to the F458. I wonder how the Italia will look like with it's roof lopped off.
The F612 in comparison is such a lengthy GT.
Fish, any of approximately 34,000 species of vertebrate animals (phylum Chordata) found in the fresh and salt waters of the world. Living species range from the primitive jawless lampreys and hagfishes through the cartilaginous sharks, skates, and rays to the abundant and diverse bony fishes. Most fish species are cold-blooded; however, one species, the opah (Lampris guttatus), is warm-blooded.
The term fish is applied to a variety of vertebrates of several evolutionary lines. It describes a life-form rather than a taxonomic group. As members of the phylum Chordata, fish share certain features with other vertebrates. These features are gill slits at some point in the life cycle, a notochord, or skeletal supporting rod, a dorsal hollow nerve cord, and a tail. Living fishes represent some five classes, which are as distinct from one another as are the four classes of familiar air-breathing animals—amphibians, reptiles, birds, and mammals. For example, the jawless fishes (Agnatha) have gills in pouches and lack limb girdles. Extant agnathans are the lampreys and the hagfishes. As the name implies, the skeletons of fishes of the class Chondrichthyes (from chondr, “cartilage,” and ichthyes, “fish”) are made entirely of cartilage. Modern fish of this class lack a swim bladder, and their scales and teeth are made up of the same placoid material. Sharks, skates, and rays are examples of cartilaginous fishes. The bony fishes are by far the largest class. Examples range from the tiny seahorse to the 450-kg (1,000-pound) blue marlin, from the flattened soles and flounders to the boxy puffers and ocean sunfishes. Unlike the scales of the cartilaginous fishes, those of bony fishes, when present, grow throughout life and are made up of thin overlapping plates of bone. Bony fishes also have an operculum that covers the gill slits.
The study of fishes, the science of ichthyology, is of broad importance. Fishes are of interest to humans for many reasons, the most important being their relationship with and dependence on the environment. A more obvious reason for interest in fishes is their role as a moderate but important part of the world’s food supply. This resource, once thought unlimited, is now realized to be finite and in delicate balance with the biological, chemical, and physical factors of the aquatic environment. Overfishing, pollution, and alteration of the environment are the chief enemies of proper fisheries management, both in fresh waters and in the ocean. (For a detailed discussion of the technology and economics of fisheries, see commercial fishing.) Another practical reason for studying fishes is their use in disease control. As predators on mosquito larvae, they help curb malaria and other mosquito-borne diseases.
Fishes are valuable laboratory animals in many aspects of medical and biological research. For example, the readiness of many fishes to acclimate to captivity has allowed biologists to study behaviour, physiology, and even ecology under relatively natural conditions. Fishes have been especially important in the study of animal behaviour, where research on fishes has provided a broad base for the understanding of the more flexible behaviour of the higher vertebrates. The zebra fish is used as a model in studies of gene expression.
There are aesthetic and recreational reasons for an interest in fishes. Millions of people keep live fishes in home aquariums for the simple pleasure of observing the beauty and behaviour of animals otherwise unfamiliar to them. Aquarium fishes provide a personal challenge to many aquarists, allowing them to test their ability to keep a small section of the natural environment in their homes. Sportfishing is another way of enjoying the natural environment, also indulged in by millions of people every year. Interest in aquarium fishes and sportfishing supports multimillion-dollar industries throughout the world.
Fishes have been in existence for more than 450 million years, during which time they have evolved repeatedly to fit into almost every conceivable type of aquatic habitat. In a sense, land vertebrates are simply highly modified fishes: when fishes colonized the land habitat, they became tetrapod (four-legged) land vertebrates. The popular conception of a fish as a slippery, streamlined aquatic animal that possesses fins and breathes by gills applies to many fishes, but far more fishes deviate from that conception than conform to it. For example, the body is elongate in many forms and greatly shortened in others; the body is flattened in some (principally in bottom-dwelling fishes) and laterally compressed in many others; the fins may be elaborately extended, forming intricate shapes, or they may be reduced or even lost; and the positions of the mouth, eyes, nostrils, and gill openings vary widely. Air breathers have appeared in several evolutionary lines.
Many fishes are cryptically coloured and shaped, closely matching their respective environments; others are among the most brilliantly coloured of all organisms, with a wide range of hues, often of striking intensity, on a single individual. The brilliance of pigments may be enhanced by the surface structure of the fish, so that it almost seems to glow. A number of unrelated fishes have actual light-producing organs. Many fishes are able to alter their coloration—some for the purpose of camouflage, others for the enhancement of behavioral signals.
Fishes range in adult length from less than 10 mm (0.4 inch) to more than 20 metres (60 feet) and in weight from about 1.5 grams (less than 0.06 ounce) to many thousands of kilograms. Some live in shallow thermal springs at temperatures slightly above 42 °C (100 °F), others in cold Arctic seas a few degrees below 0 °C (32 °F) or in cold deep waters more than 4,000 metres (13,100 feet) beneath the ocean surface. The structural and, especially, the physiological adaptations for life at such extremes are relatively poorly known and provide the scientifically curious with great incentive for study.
Almost all natural bodies of water bear fish life, the exceptions being very hot thermal ponds and extremely salt-alkaline lakes, such as the Dead Sea in Asia and the Great Salt Lake in North America. The present distribution of fishes is a result of the geological history and development of Earth as well as the ability of fishes to undergo evolutionary change and to adapt to the available habitats. Fishes may be seen to be distributed according to habitat and according to geographical area. Major habitat differences are marine and freshwater. For the most part, the fishes in a marine habitat differ from those in a freshwater habitat, even in adjacent areas, but some, such as the salmon, migrate from one to the other. The freshwater habitats may be seen to be of many kinds. Fishes found in mountain torrents, Arctic lakes, tropical lakes, temperate streams, and tropical rivers will all differ from each other, both in obvious gross structure and in physiological attributes. Even in closely adjacent habitats where, for example, a tropical mountain torrent enters a lowland stream, the fish fauna will differ. The marine habitats can be divided into deep ocean floors (benthic), mid-water oceanic (bathypelagic), surface oceanic (pelagic), rocky coast, sandy coast, muddy shores, bays, estuaries, and others. Also, for example, rocky coastal shores in tropical and temperate regions will have different fish faunas, even when such habitats occur along the same coastline.
Although much is known about the present geographical distribution of fishes, far less is known about how that distribution came about. Many parts of the fish fauna of the fresh waters of North America and Eurasia are related and undoubtedly have a common origin. The faunas of Africa and South America are related, extremely old, and probably an expression of the drifting apart of the two continents. The fauna of southern Asia is related to that of Central Asia, and some of it appears to have entered Africa. The extremely large shore-fish faunas of the Indian and tropical Pacific oceans comprise a related complex, but the tropical shore fauna of the Atlantic, although containing Indo-Pacific components, is relatively limited and probably younger. The Arctic and Antarctic marine faunas are quite different from each other. The shore fauna of the North Pacific is quite distinct, and that of the North Atlantic more limited and probably younger. Pelagic oceanic fishes, especially those in deep waters, are similar the world over, showing little geographical isolation in terms of family groups. The deep oceanic habitat is very much the same throughout the world, but species differences do exist, showing geographical areas determined by oceanic currents and water masses.
All aspects of the life of a fish are closely correlated with adaptation to the total environment, physical, chemical, and biological. In studies, all the interdependent aspects of fish, such as behaviour, locomotion, reproduction, and physical and physiological characteristics, must be taken into account.
Correlated with their adaptation to an extremely wide variety of habitats is the extremely wide variety of life cycles that fishes display. The great majority hatch from relatively small eggs a few days to several weeks or more after the eggs are scattered in the water. Newly hatched young are still partially undeveloped and are called larvae until body structures such as fins, skeleton, and some organs are fully formed. Larval life is often very short, usually less than a few weeks, but it can be very long, some lampreys continuing as larvae for at least five years. Young and larval fishes, before reaching sexual maturity, must grow considerably, and their small size and other factors often dictate that they live in a habitat different than that of the adults. For example, most tropical marine shore fishes have pelagic larvae. Larval food also is different, and larval fishes often live in shallow waters, where they may be less exposed to predators.
After a fish reaches adult size, the length of its life is subject to many factors, such as innate rates of aging, predation pressure, and the nature of the local climate. The longevity of a species in the protected environment of an aquarium may have nothing to do with how long members of that species live in the wild. Many small fishes live only one to three years at the most. In some species, however, individuals may live as long as 10 or 20 or even 100 years.
Fish behaviour is a complicated and varied subject. As in almost all animals with a central nervous system, the nature of a response of an individual fish to stimuli from its environment depends upon the inherited characteristics of its nervous system, on what it has learned from past experience, and on the nature of the stimuli. Compared with the variety of human responses, however, that of a fish is stereotyped, not subject to much modification by “thought” or learning, and investigators must guard against anthropomorphic interpretations of fish behaviour.
Fishes perceive the world around them by the usual senses of sight, smell, hearing, touch, and taste and by special lateral line water-current detectors. In the few fishes that generate electric fields, a process that might best be called electrolocation aids in perception. One or another of these senses often is emphasized at the expense of others, depending upon the fish’s other adaptations. In fishes with large eyes, the sense of smell may be reduced; others, with small eyes, hunt and feed primarily by smell (such as some eels).
Specialized behaviour is primarily concerned with the three most important activities in the fish’s life: feeding, reproduction, and escape from enemies. Schooling behaviour of sardines on the high seas, for instance, is largely a protective device to avoid enemies, but it is also associated with and modified by their breeding and feeding requirements. Predatory fishes are often solitary, lying in wait to dart suddenly after their prey, a kind of locomotion impossible for beaked parrot fishes, which feed on coral, swimming in small groups from one coral head to the next. In addition, some predatory fishes that inhabit pelagic environments, such as tunas, often school.
Sleep in fishes, all of which lack true eyelids, consists of a seemingly listless state in which the fish maintains its balance but moves slowly. If attacked or disturbed, most can dart away. A few kinds of fishes lie on the bottom to sleep. Most catfishes, some loaches, and some eels and electric fishes are strictly nocturnal, being active and hunting for food during the night and retiring during the day to holes, thick vegetation, or other protective parts of the environment.
Communication between members of a species or between members of two or more species often is extremely important, especially in breeding behaviour (see below Reproduction). The mode of communication may be visual, as between the small so-called cleaner fish and a large fish of a very different species. The larger fish often allows the cleaner to enter its mouth to remove gill parasites. The cleaner is recognized by its distinctive colour and actions and therefore is not eaten, even if the larger fish is normally a predator. Communication is often chemical, signals being sent by specific chemicals called pheromones.
Many fishes have a streamlined body and swim freely in open water. Fish locomotion is closely correlated with habitat and ecological niche (the general position of the animal to its environment).
Many fishes in both marine and fresh waters swim at the surface and have mouths adapted to feed best (and sometimes only) at the surface. Often such fishes are long and slender, able to dart at surface insects or at other surface fishes and in turn to dart away from predators; needlefishes, halfbeaks, and topminnows (such as killifish and mosquito fish) are good examples. Oceanic flying fishes escape their predators by gathering speed above the water surface, with the lower lobe of the tail providing thrust in the water. They then glide hundreds of yards on enlarged, winglike pectoral and pelvic fins. South American freshwater flying fishes escape their enemies by jumping and propelling their strongly keeled bodies out of the water.
So-called mid-water swimmers, the most common type of fish, are of many kinds and live in many habitats. The powerful fusiform tunas and the trouts, for example, are adapted for strong, fast swimming, the tunas to capture prey speedily in the open ocean and the trouts to cope with the swift currents of streams and rivers. The trout body form is well adapted to many habitats. Fishes that live in relatively quiet waters such as bays or lake shores or slow rivers usually are not strong, fast swimmers but are capable of short, quick bursts of speed to escape a predator. Many of these fishes have their sides flattened, examples being the sunfish and the freshwater angelfish of aquarists. Fish associated with the bottom or substrate usually are slow swimmers. Open-water plankton-feeding fishes almost always remain fusiform and are capable of rapid, strong movement (for example, sardines and herrings of the open ocean and also many small minnows of streams and lakes).
Bottom-living fishes are of many kinds and have undergone many types of modification of their body shape and swimming habits. Rays, which evolved from strong-swimming mid-water sharks, usually stay close to the bottom and move by undulating their large pectoral fins. Flounders live in a similar habitat and move over the bottom by undulating the entire body. Many bottom fishes dart from place to place, resting on the bottom between movements, a motion common in gobies. One goby relative, the mudskipper, has taken to living at the edge of pools along the shore of muddy mangrove swamps. It escapes its enemies by flipping rapidly over the mud, out of the water. Some catfishes, synbranchid eels, the so-called climbing perch, and a few other fishes venture out over damp ground to find more promising waters than those that they left. They move by wriggling their bodies, sometimes using strong pectoral fins; most have accessory air-breathing organs. Many bottom-dwelling fishes live in mud holes or rocky crevices. Marine eels and gobies commonly are found in such habitats and for the most part venture far beyond their cavelike homes. Some bottom dwellers, such as the clingfishes (Gobiesocidae), have developed powerful adhesive disks that enable them to remain in place on the substrate in areas such as rocky coasts, where the action of the waves is great.
The methods of reproduction in fishes are varied, but most fishes lay a large number of small eggs, fertilized and scattered outside of the body. The eggs of pelagic fishes usually remain suspended in the open water. Many shore and freshwater fishes lay eggs on the bottom or among plants. Some have adhesive eggs. The mortality of the young and especially of the eggs is very high, and often only a few individuals grow to maturity out of hundreds, thousands, and in some cases millions of eggs laid.
Males produce sperm, usually as a milky white substance called milt, in two (sometimes one) testes within the body cavity. In bony fishes a sperm duct leads from each testis to a urogenital opening behind the vent or anus. In sharks and rays and in cyclostomes the duct leads to a cloaca. Sometimes the pelvic fins are modified to help transmit the milt to the eggs at the female’s vent or on the substrate where the female has placed them. Sometimes accessory organs are used to fertilize females internally—for example, the claspers of many sharks and rays.
In the females the eggs are formed in two ovaries (sometimes only one) and pass through the ovaries to the urogenital opening and to the outside. In some fishes the eggs are fertilized internally but are shed before development takes place. Members of about a dozen families each of bony fishes (teleosts) and sharks bear live young. Many skates and rays also bear live young. In some bony fishes the eggs simply develop within the female, the young emerging when the eggs hatch (ovoviviparous). Others develop within the ovary and are nourished by ovarian tissues after hatching (viviparous). There are also other methods utilized by fishes to nourish young within the female. In all live-bearers the young are born at a relatively large size and are few in number. In one family of primarily marine fishes, the surfperches from the Pacific coast of North America, Japan, and Korea, the males of at least one species are born sexually mature, although they are not fully grown.
Some fishes are hermaphroditic—an individual producing both sperm and eggs, usually at different stages of its life. Self-fertilization, however, is probably rare.
Successful reproduction and, in many cases, defense of the eggs and the young are assured by rather stereotypical but often elaborate courtship and parental behaviour, either by the male or the female or both. Some fishes prepare nests by hollowing out depressions in the sand bottom (cichlids, for example), build nests with plant materials and sticky threads excreted by the kidneys (sticklebacks), or blow a cluster of mucus-covered bubbles at the water surface (gouramis). The eggs are laid in these structures. Some varieties of cichlids and catfishes incubate eggs in their mouths.
Some fishes, such as salmon, undergo long migrations from the ocean and up large rivers to spawn in the gravel beds where they themselves hatched (anadromous fishes). Some, such as the freshwater eels (family Anguillidae), live and grow to maturity in fresh water and migrate to the sea to spawn (catadromous fishes). Other fishes undertake shorter migrations from lakes into streams, within the ocean, or enter spawning habitats that they do not ordinarily occupy in other ways.
The basic structure and function of the fish body are similar to those of all other vertebrates. The usual four types of tissues are present: surface or epithelial, connective (bone, cartilage, and fibrous tissues, as well as their derivative, blood), nerve, and muscle tissues. In addition, the fish’s organs and organ systems parallel those of other vertebrates.
The typical fish body is streamlined and spindle-shaped, with an anterior head, a gill apparatus, and a heart, the latter lying in the midline just below the gill chamber. The body cavity, containing the vital organs, is situated behind the head in the lower anterior part of the body. The anus usually marks the posterior termination of the body cavity and most often occurs just in front of the base of the anal fin. The spinal cord and vertebral column continue from the posterior part of the head to the base of the tail fin, passing dorsal to the body cavity and through the caudal (tail) region behind the body cavity. Most of the body is of muscular tissue, a high proportion of which is necessitated by swimming. In the course of evolution this basic body plan has been modified repeatedly into the many varieties of fish shapes that exist today.
The skeleton forms an integral part of the fish’s locomotion system, as well as serving to protect vital parts. The internal skeleton consists of the skull bones (except for the roofing bones of the head, which are really part of the external skeleton), the vertebral column, and the fin supports (fin rays). The fin supports are derived from the external skeleton but will be treated here because of their close functional relationship to the internal skeleton. The internal skeleton of cyclostomes, sharks, and rays is of cartilage; that of many fossil groups and some primitive living fishes is mostly of cartilage but may include some bone. In place of the vertebral column, the earliest vertebrates had a fully developed notochord, a flexible stiff rod of viscous cells surrounded by a strong fibrous sheath. During the evolution of modern fishes the rod was replaced in part by cartilage and then by ossified cartilage. Sharks and rays retain a cartilaginous vertebral column; bony fishes have spool-shaped vertebrae that in the more primitive living forms only partially replace the notochord. The skull, including the gill arches and jaws of bony fishes, is fully, or at least partially, ossified. That of sharks and rays remains cartilaginous, at times partially replaced by calcium deposits but never by true bone.
The supportive elements of the fins (basal or radial bones or both) have changed greatly during fish evolution. Some of these changes are described in the section below (Evolution and paleontology). Most fishes possess a single dorsal fin on the midline of the back. Many have two and a few have three dorsal fins. The other fins are the single tail and anal fins and paired pelvic and pectoral fins. A small fin, the adipose fin, with hairlike fin rays, occurs in many of the relatively primitive teleosts (such as trout) on the back near the base of the caudal fin.
The skin of a fish must serve many functions. It aids in maintaining the osmotic balance, provides physical protection for the body, is the site of coloration, contains sensory receptors, and, in some fishes, functions in respiration. Mucous glands, which aid in maintaining the water balance and offer protection from bacteria, are extremely numerous in fish skin, especially in cyclostomes and teleosts. Since mucous glands are present in the modern lampreys, it is reasonable to assume that they were present in primitive fishes, such as the ancient Silurian and Devonian agnathans. Protection from abrasion and predation is another function of the fish skin, and dermal (skin) bone arose early in fish evolution in response to this need. It is thought that bone first evolved in skin and only later invaded the cartilaginous areas of the fish’s body, to provide additional support and protection. There is some argument as to which came first, cartilage or bone, and fossil evidence does not settle the question. In any event, dermal bone has played an important part in fish evolution and has different characteristics in different groups of fishes. Several groups are characterized at least in part by the kind of bony scales they possess.
Scales have played an important part in the evolution of fishes. Primitive fishes usually had thick bony plates or thick scales in several layers of bone, enamel, and related substances. Modern teleost fishes have scales of bone, which, while still protective, allow much more freedom of motion in the body. A few modern teleosts (some catfishes, sticklebacks, and others) have secondarily acquired bony plates in the skin. Modern and early sharks possessed placoid scales, a relatively primitive type of scale with a toothlike structure, consisting of an outside layer of enamel-like substance (vitrodentine), an inner layer of dentine, and a pulp cavity containing nerves and blood vessels. Primitive bony fishes had thick scales of either the ganoid or the cosmoid type. Cosmoid scales have a hard, enamel-like outer layer, an inner layer of cosmine (a form of dentine), and then a layer of vascular bone (isopedine). In ganoid scales the hard outer layer is different chemically and is called ganoin. Under this is a cosminelike layer and then a vascular bony layer. The thin, translucent bony scales of modern fishes, called cycloid and ctenoid (the latter distinguished by serrations at the edges), lack enameloid and dentine layers.
Skin has several other functions in fishes. It is well supplied with nerve endings and presumably receives tactile, thermal, and pain stimuli. Skin is also well supplied with blood vessels. Some fishes breathe in part through the skin, by the exchange of oxygen and carbon dioxide between the surrounding water and numerous small blood vessels near the skin surface.
Skin serves as protection through the control of coloration. Fishes exhibit an almost limitless range of colours. The colours often blend closely with the surroundings, effectively hiding the animal. Many fishes use bright colours for territorial advertisement or as recognition marks for other members of their own species, or sometimes for members of other species. Many fishes can change their colour to a greater or lesser degree, by movement of pigment within the pigment cells (chromatophores). Black pigment cells (melanophores), of almost universal occurrence in fishes, are often juxtaposed with other pigment cells. When placed beneath iridocytes or leucophores (bearing the silvery or white pigment guanine), melanophores produce structural colours of blue and green. These colours are often extremely intense, because they are formed by refraction of light through the needlelike crystals of guanine. The blue and green refracted colours are often relatively pure, lacking the red and yellow rays, which have been absorbed by the black pigment (melanin) of the melanophores. Yellow, orange, and red colours are produced by erythrophores, cells containing the appropriate carotenoid pigments. Other colours are produced by combinations of melanophores, erythrophores, and iridocytes.
The major portion of the body of most fishes consists of muscles. Most of the mass is trunk musculature, the fin muscles usually being relatively small. The caudal fin is usually the most powerful fin, being moved by the trunk musculature. The body musculature is usually arranged in rows of chevron-shaped segments on each side. Contractions of these segments, each attached to adjacent vertebrae and vertebral processes, bends the body on the vertebral joint, producing successive undulations of the body, passing from the head to the tail, and producing driving strokes of the tail. It is the latter that provides the strong forward movement for most fishes.
The digestive system, in a functional sense, starts at the mouth, with the teeth used to capture prey or collect plant foods. Mouth shape and tooth structure vary greatly in fishes, depending on the kind of food normally eaten. Most fishes are predacious, feeding on small invertebrates or other fishes and have simple conical teeth on the jaws, on at least some of the bones of the roof of the mouth, and on special gill arch structures just in front of the esophagus. The latter are throat teeth. Most predacious fishes swallow their prey whole, and the teeth are used for grasping and holding prey, for orienting prey to be swallowed (head first) and for working the prey toward the esophagus. There are a variety of tooth types in fishes. Some fishes, such as sharks and piranhas, have cutting teeth for biting chunks out of their victims. A shark’s tooth, although superficially like that of a piranha, appears in many respects to be a modified scale, while that of the piranha is like that of other bony fishes, consisting of dentine and enamel. Parrot fishes have beaklike mouths with short incisor-like teeth for breaking off coral and have heavy pavementlike throat teeth for crushing the coral. Some catfishes have small brushlike teeth, arranged in rows on the jaws, for scraping plant and animal growth from rocks. Many fishes (such as the Cyprinidae or minnows) have no jaw teeth at all but have very strong throat teeth.
Some fishes gather planktonic food by straining it from their gill cavities with numerous elongate stiff rods (gill rakers) anchored by one end to the gill bars. The food collected on these rods is passed to the throat, where it is swallowed. Most fishes have only short gill rakers that help keep food particles from escaping out the mouth cavity into the gill chamber.
Once reaching the throat, food enters a short, often greatly distensible esophagus, a simple tube with a muscular wall leading into a stomach. The stomach varies greatly in fishes, depending upon the diet. In most predacious fishes it is a simple straight or curved tube or pouch with a muscular wall and a glandular lining. Food is largely digested there and leaves the stomach in liquid form.
Between the stomach and the intestine, ducts enter the digestive tube from the liver and pancreas. The liver is a large, clearly defined organ. The pancreas may be embedded in it, diffused through it, or broken into small parts spread along some of the intestine. The junction between the stomach and the intestine is marked by a muscular valve. Pyloric ceca (blind sacs) occur in some fishes at this junction and have a digestive or absorptive function or both.
The intestine itself is quite variable in length, depending upon the fish’s diet. It is short in predacious forms, sometimes no longer than the body cavity, but long in herbivorous forms, being coiled and several times longer than the entire length of the fish in some species of South American catfishes. The intestine is primarily an organ for absorbing nutrients into the bloodstream. The larger its internal surface, the greater its absorptive efficiency, and a spiral valve is one method of increasing its absorption surface.
Sharks, rays, chimaeras, lungfishes, surviving chondrosteans, holosteans, and even a few of the more primitive teleosts have a spiral valve or at least traces of it in the intestine. Most modern teleosts have increased the area of the intestinal walls by having numerous folds and villi (fingerlike projections) somewhat like those in humans. Undigested substances are passed to the exterior through the anus in most teleost fishes. In lungfishes, sharks, and rays, it is first passed through the cloaca, a common cavity receiving the intestinal opening and the ducts from the urogenital system.
Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills. The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour. Water taken in continuously through the mouth passes backward between the gill bars and over the gill filaments, where the exchange of gases takes place. The gills are protected by a gill cover in teleosts and many other fishes but by flaps of skin in sharks, rays, and some of the older fossil fish groups. The blood capillaries in the gill filaments are close to the gill surface to take up oxygen from the water and to give up excess carbon dioxide to the water.
Most modern fishes have a hydrostatic (ballast) organ, called the swim bladder, that lies in the body cavity just below the kidney and above the stomach and intestine. It originated as a diverticulum of the digestive canal. In advanced teleosts, especially the acanthopterygians, the bladder has lost its connection with the digestive tract, a condition called physoclistic. The connection has been retained (physostomous) by many relatively primitive teleosts. In several unrelated lines of fishes, the bladder has become specialized as a lung or, at least, as a highly vascularized accessory breathing organ. Some fishes with such accessory organs are obligate air breathers and will drown if denied access to the surface, even in well-oxygenated water. Fishes with a hydrostatic form of swim bladder can control their depth by regulating the amount of gas in the bladder. The gas, mostly oxygen, is secreted into the bladder by special glands, rendering the fish more buoyant; the gas is absorbed into the bloodstream by another special organ, reducing the overall buoyancy and allowing the fish to sink. Some deep-sea fishes may have oils, rather than gas, in the bladder. Other deep-sea and some bottom-living forms have much-reduced swim bladders or have lost the organ entirely.
The swim bladder of fishes follows the same developmental pattern as the lungs of land vertebrates. There is no doubt that the two structures have the same historical origin in primitive fishes. More or less intermediate forms still survive among the more primitive types of fishes, such as the lungfishes Lepidosiren and Protopterus.
The circulatory, or blood vascular, system consists of the heart, the arteries, the capillaries, and the veins. It is in the capillaries that the interchange of oxygen, carbon dioxide, nutrients, and other substances such as hormones and waste products takes place. The capillaries lead to the veins, which return the venous blood with its waste products to the heart, kidneys, and gills. There are two kinds of capillary beds: those in the gills and those in the rest of the body. The heart, a folded continuous muscular tube with three or four saclike enlargements, undergoes rhythmic contractions and receives venous blood in a sinus venosus. It passes the blood to an auricle and then into a thick muscular pump, the ventricle. From the ventricle the blood goes to a bulbous structure at the base of a ventral aorta just below the gills. The blood passes to the afferent (receiving) arteries of the gill arches and then to the gill capillaries. There waste gases are given off to the environment, and oxygen is absorbed. The oxygenated blood enters efferent (exuant) arteries of the gill arches and then flows into the dorsal aorta. From there blood is distributed to the tissues and organs of the body. One-way valves prevent backflow. The circulation of fishes thus differs from that of the reptiles, birds, and mammals in that oxygenated blood is not returned to the heart prior to distribution to the other parts of the body.
The primary excretory organ in fishes, as in other vertebrates, is the kidney. In fishes some excretion also takes place in the digestive tract, skin, and especially the gills (where ammonia is given off). Compared with land vertebrates, fishes have a special problem in maintaining their internal environment at a constant concentration of water and dissolved substances, such as salts. Proper balance of the internal environment (homeostasis) of a fish is in a great part maintained by the excretory system, especially the kidney.
The kidney, gills, and skin play an important role in maintaining a fish’s internal environment and checking the effects of osmosis. Marine fishes live in an environment in which the water around them has a greater concentration of salts than they can have inside their body and still maintain life. Freshwater fishes, on the other hand, live in water with a much lower concentration of salts than they require inside their bodies. Osmosis tends to promote the loss of water from the body of a marine fish and absorption of water by that of a freshwater fish. Mucus in the skin tends to slow the process but is not a sufficient barrier to prevent the movement of fluids through the permeable skin. When solutions on two sides of a permeable membrane have different concentrations of dissolved substances, water will pass through the membrane into the more concentrated solution, while the dissolved chemicals move into the area of lower concentration (diffusion).
The kidney of freshwater fishes is often larger in relation to body weight than that of marine fishes. In both groups the kidney excretes wastes from the body, but the kidney of freshwater fishes also excretes large amounts of water, counteracting the water absorbed through the skin. Freshwater fishes tend to lose salt to the environment and must replace it. They get some salt from their food, but the gills and skin inside the mouth actively absorb salt from water passed through the mouth. This absorption is performed by special cells capable of moving salts against the diffusion gradient. Freshwater fishes drink very little water and take in little water with their food.
Marine fishes must conserve water, and therefore their kidneys excrete little water. To maintain their water balance, marine fishes drink large quantities of seawater, retaining most of the water and excreting the salt. Most nitrogenous waste in marine fishes appears to be secreted by the gills as ammonia. Marine fishes can excrete salt by clusters of special cells (chloride cells) in the gills.
There are several teleosts—for example, the salmon—that travel between fresh water and seawater and must adjust to the reversal of osmotic gradients. They adjust their physiological processes by spending time (often surprisingly little time) in the intermediate brackish environment.
Marine hagfishes, sharks, and rays have osmotic concentrations in their blood about equal to that of seawater and so do not have to drink water nor perform much physiological work to maintain their osmotic balance. In sharks and rays the osmotic concentration is kept high by retention of urea in the blood. Freshwater sharks have a lowered concentration of urea in the blood.
Endocrine glands secrete their products into the bloodstream and body tissues and, along with the central nervous system, control and regulate many kinds of body functions. Cyclostomes have a well-developed endocrine system, and presumably it was well developed in the early Agnatha, ancestral to modern fishes. Although the endocrine system in fishes is similar to that of higher vertebrates, there are numerous differences in detail. The pituitary, the thyroid, the suprarenals, the adrenals, the pancreatic islets, the sex glands (ovaries and testes), the inner wall of the intestine, and the bodies of the ultimobranchial gland make up the endocrine system in fishes. There are some others whose function is not well understood. These organs regulate sexual activity and reproduction, growth, osmotic pressure, general metabolic activities such as the storage of fat and the utilization of foodstuffs, blood pressure, and certain aspects of skin colour. Many of these activities are also controlled in part by the central nervous system, which works with the endocrine system in maintaining the life of a fish. Some parts of the endocrine system are developmentally, and undoubtedly evolutionarily, derived from the nervous system.
As in all vertebrates, the nervous system of fishes is the primary mechanism coordinating body activities, as well as integrating these activities in the appropriate manner with stimuli from the environment. The central nervous system, consisting of the brain and spinal cord, is the primary integrating mechanism. The peripheral nervous system, consisting of nerves that connect the brain and spinal cord to various body organs, carries sensory information from special receptor organs such as the eyes, internal ears, nares (sense of smell), taste glands, and others to the integrating centres of the brain and spinal cord. The peripheral nervous system also carries information via different nerve cells from the integrating centres of the brain and spinal cord. This coded information is carried to the various organs and body systems, such as the skeletal muscular system, for appropriate action in response to the original external or internal stimulus. Another branch of the nervous system, the autonomic nervous system, helps to coordinate the activities of many glands and organs and is itself closely connected to the integrating centres of the brain.
The brain of the fish is divided into several anatomical and functional parts, all closely interconnected but each serving as the primary centre of integrating particular kinds of responses and activities. Several of these centres or parts are primarily associated with one type of sensory perception, such as sight, hearing, or smell (olfaction).
The sense of smell is important in almost all fishes. Certain eels with tiny eyes depend mostly on smell for location of food. The olfactory, or nasal, organ of fishes is located on the dorsal surface of the snout. The lining of the nasal organ has special sensory cells that perceive chemicals dissolved in the water, such as substances from food material, and send sensory information to the brain by way of the first cranial nerve. Odour also serves as an alarm system. Many fishes, especially various species of freshwater minnows, react with alarm to a chemical released from the skin of an injured member of their own species.
Many fishes have a well-developed sense of taste, and tiny pitlike taste buds or organs are located not only within their mouth cavities but also over their heads and parts of their body. Catfishes, which often have poor vision, have barbels (“whiskers”) that serve as supplementary taste organs, those around the mouth being actively used to search out food on the bottom. Some species of naturally blind cave fishes are especially well supplied with taste buds, which often cover most of their body surface.
Sight is extremely important in most fishes. The eye of a fish is basically like that of all other vertebrates, but the eyes of fishes are extremely varied in structure and adaptation. In general, fishes living in dark and dim water habitats have large eyes, unless they have specialized in some compensatory way so that another sense (such as smell) is dominant, in which case the eyes will often be reduced. Fishes living in brightly lighted shallow waters often will have relatively small but efficient eyes. Cyclostomes have somewhat less elaborate eyes than other fishes, with skin stretched over the eyeball perhaps making their vision somewhat less effective. Most fishes have a spherical lens and accommodate their vision to far or near subjects by moving the lens within the eyeball. A few sharks accommodate by changing the shape of the lens, as in land vertebrates. Those fishes that are heavily dependent upon the eyes have especially strong muscles for accommodation. Most fishes see well, despite the restrictions imposed by frequent turbidity of the water and by light refraction.
Fossil evidence suggests that colour vision evolved in fishes more than 300 million years ago, but not all living fishes have retained this ability. Experimental evidence indicates that many shallow-water fishes, if not all, have colour vision and see some colours especially well, but some bottom-dwelling shore fishes live in areas where the water is sufficiently deep to filter out most if not all colours, and these fishes apparently never see colours. When tested in shallow water, they apparently are unable to respond to colour differences.
Sound perception and balance are intimately associated senses in a fish. The organs of hearing are entirely internal, located within the skull, on each side of the brain and somewhat behind the eyes. Sound waves, especially those of low frequencies, travel readily through water and impinge directly upon the bones and fluids of the head and body, to be transmitted to the hearing organs. Fishes readily respond to sound; for example, a trout conditioned to escape by the approach of fishermen will take flight upon perceiving footsteps on a stream bank even if it cannot see a fisherman. Compared with humans, however, the range of sound frequencies heard by fishes is greatly restricted. Many fishes communicate with each other by producing sounds in their swim bladders, in their throats by rasping their teeth, and in other ways.
A fish or other vertebrate seldom has to rely on a single type of sensory information to determine the nature of the environment around it. A catfish uses taste and touch when examining a food object with its oral barbels. Like most other animals, fishes have many touch receptors over their body surface. Pain and temperature receptors also are present in fishes and presumably produce the same kind of information to a fish as to humans. Fishes react in a negative fashion to stimuli that would be painful to human beings, suggesting that they feel a sensation of pain.
An important sensory system in fishes that is absent in other vertebrates (except some amphibians) is the lateral line system. This consists of a series of heavily innervated small canals located in the skin and bone around the eyes, along the lower jaw, over the head, and down the mid-side of the body, where it is associated with the scales. Intermittently along these canals are located tiny sensory organs (pit organs) that apparently detect changes in pressure. The system allows a fish to sense changes in water currents and pressure, thereby helping the fish to orient itself to the various changes that occur in the physical environment.
The hangings are like a missed light on Lucifer's forehead, it's probably a pending question for a gargoyle game.... What is the deep understanding of the creature suspended on Freiburg Cathedral in Breisgau? Much rain fell and the question remained suspended to the scepticism of official historians? while a Green Serpent read JW Goethe and fed on the heart of this stone suspended above our consciences limited by many proud clouds. The gargoyles are used to evacuate the flow of three-dimensional logic. The layer of paint forgotten by the architects of the Spirit limited by the green moss that invades their sectarian thoughts.
Just after the Flood, at the dawn of the current cycle, an era that the Egyptians called ZEP TEPI, "The First Times", a mysterious group of "gods", appeared to introduce the survivors to the rudiments of civilization. From Thoth and Osiris in Egypt to Quetzacoatal and Viracocha in the Americas, traditions around the world are bringing the origins of contemporary civilization into this sophisticated group. The creatures hanging on the top are suffering a flood, they have been vomiting since the dawn of time, but unfortunately we have lost their flood of messages. The East has nourished this Rhine land for centuries, today we are in ethnocentric explanations.....
Despite the misleading popularity of Von Danikan journalism, evidence from around the world, indicates these people were the hi-tech survivors of the previous civilisation. Like the nuclear survival bunkers and secret research facilities of our civilisation, there were those who arose from the underground "cities of the Gods", after the dust settled. They were the "prediluvian patriarchs", like Enoch and Methuselah, the "giants and heroes of old", mentioned in Genesis.
The enigmatic gods ancient Summer, Egypt and India, all hail from the fabulous times before the Flood. Since the declassification of the new ground-penetrating radar 2 years ago, the most staggering data has emerged of complex and labyrinthine underground systems in various parts of the world. At places like Guatemala in the South Americas, tunnels have been mapped under the Mayan pyramid complex at Tikal, which extend a full 800 kilometres to the opposite side of the country. Investigators remarked, it was possible to understand how half a million Mayan Indians escaped the decimation of their culture.
In similar fashion, the SIRA radar was deployed in Egypt as early as 1978, mapping an extraordinary subterranean complex beneath the Egyptian pyramids. Arrangements made with President Sadat of Egypt, resulted in three decades of top secret excavations to penetrate the system. At a recent meeting in Australia, one of the key scientists on the Giza project, Dr. Jim Hurtak, showed film footage of work in progress called, CHAMBERS OF THE DEEP, due to be released at the end of the century. The film reveals the discovery of a vast megalithic metropolis, 15,000 years old, reaching several levels below the Giza plateau.
While the rest of the Nu-Age speculates about a hidden chamber under the left paw of the Sphinx, the legendary "City Of The Gods", lays sprawled beneath. Complete with hydraulic underground waterways, the film shows massive chambers, the proportions of our largest cathedrals, with enormous statues, the size of the Valley of the Nile, carved in-situ. Researchers, risking their lives with lights and cameras, carefully negotiated rubber dinghies across subterranean rivers and kilometer-wide lakes, to penetrate sealed chambers beyond. Already, remarkable caches of records and artifacts have been found. It is the legacy of a civilisation and a technology way beyond our own. A technology capable of creating a vast underground city, of which the sphinx and pyramids are merely the surface markers. The project scientist, Dr. Hurtak, likens it to the impact of contact with an advanced extraterrestrial culture. He described it as the discovery of the Fourth Root culture, the so-called Atlantean civilisation, destroyed by the last earth tumble. It presents unequivocal evidence that all languages, cultures and religions trace back to a single common source, which Dr. Hurtak refers to as the "Parent Civilisation".
The technology unearthed is way beyond machine technology, as we know it. As Arthur C. Clark once joked, "any technology beyond our own would seem like magic to us." According to Dr. Hurtak, this was a culture who cracked the genetic code and possessed the keys of the physical spectrum, the "Higher Light Physics" of the ancients... everything old Gilgamesh went searching for in his famous trek to the lost "City of the Gods" to search the tunnels beneath "Mt. Mashu" in the desert lands.
Hurtak refers to a "language of light" and a great priest-scientist of the previous time cycle, named ENOCH, who is associated with the building of the Great Pyramid complex. Hurtak alludes to a grand spiritual science, a science which describes a genetic stairway to the stars. The priest-scientist ENOCH, is a prediluvian patriarch, one of the most famous and seminal characters of the previous time cycle. Father of Methuselah and great grandfather of Noah, Enoch is credited in the Bible as architect of the original Zion, the legendary "City of Yahweh", as well as inventor of the alphabet and calendar. Enoch is also history's first astronaut, who "is taken aloft by the Lord" and shown "the secrets of earth and heaven". He returns to earth with the "weights and measures" for all humankind.
Known to the Egyptians as THOTH, the "Lord of Magic and Time" and to theGreeks as HERMES, "messenger of the gods", he is even remembered in the Celtic tradition as the enigmatic wizard Merlin, who disappears up an apple tree to mythic Avalon, seeking the secret of immortality and vowing to return. As one who attained immortality, the secret of how we "might become as gods", Thoth/Enoch promises to return at the end of time "with the keys to the gates of the sacred land."
In the controversial Dead Sea Scrolls, revealing the lost Books Of Enoch removed from the Bible by early religious leaders, Enoch describes a wondrous civilisation in the past, who misused the keys of higher knowledge and were unable to save themselves from the last cataclysm. Both literally and figuratively they lost the "keys", they lost all higher knowledge.Yet, Enoch, along with many traditions, even the Mayan legend of Quetzacoatal, promises a return of this knowledge at "The end of time", the end of the present time cycle.
Biblical Revelations promise "all will be revealed" at the end of the present world. The extraordinary discoveries in Egypt and other parts of the world, describe not just an advanced technology but, evolutionary path beyond our present state. Careful scientific examination of the world's key pyramid sites, reveal them to be sophisticated harmonic structures, not only mirroring positions of the planets and stellar systems but, designed to mimic the chakras and harmonic cavities of the human body. Even each stone within the Great Pyramid is harmonically tuned to a specific frequency or musical tone. The sarcophagus in the centre of the Great Pyramid is tuned to the frequency of the human heart beat. Astonishing experiments, conducted by Dr. Hurtak and colleagues at the Great Pyramid and other sites in the South Americas, demonstrate the pyramids to be voice-activated "geophysical computers."
Intoning specific ancient sounds, the scientific team produced visible standing waves of light, above and within the pyramids and were even able to penetrate, hitherto, inaccessible chambers. Subsequent discoveries indicate the ancient priest-scientists employed some sort of harmonic sound technology within the temple structures. The lost Enochian knowledge reveals the mother tongue as a "language of Light". Known to the ancients as HIBURU, it is the primal seed language, introduced at the beginning of this time cycle.
Modern research confirms, the most ancient form Hebrew to be a natural language, the alphabetic forms emerging from the phosphene flare patterns of the brain. The same shapes, in fact, born of a spinning vortex. It is a true language of light, coursing through our very nervous system. Encoding the natural waveform geometries of the physical world, Hiburu is a harmonic language, mimicking the waveform properties of light.
The "keys" Enoch speaks of, turn out to be sound keys, keys to be vibratory matrix of reality itself, the mythic "Power of the World". The Enochian knowledge describes sonic equations, encoded within the ancient mantras and god names, capable of directly affect the nervous system and producing profound effect of healing and higher consciousness states. As the ancient texts declare, "If you would speak with the gods you must first learn the language of the gods."
DNA, the ancient cabalistic "Tree Of Life" portrayed in the Biblical Torah, is now coming to be viewed as a live vibrating structure, rather than a fixed tape recording. Many modern scientists, regard DNA as a shimmering, waveform configuration, able to be modified by light, radiation, magnetic fields or sonic pulses. The legacy of Thoth/Enoch suggests this "language of Light", the harmonic science of the ancients, could actually affect DNA. The evidence in Egypt, indicates this was the grand 6,000 year genetic experiment attempted by the Egyptians, the quest for immortality and the stars, a quest described by the great ones of old, a quest initiated by Gilgamesh so very long ago.
The Egyptians were not fixated on the afterlife, as thought by early Christian translators but, focussed on creating a higher type of human. Along with many ancient cultures, they believed DNA came from the stars and was destined to return.The knowledge of Thoth/Enoch implies humans are meant to evolve beyond our present terrestrial form, as the Bible tells us, "we may become greater than angels".The Egyptians record stories of the "Star Walkers", occasional individuals who, like Enoch, travelled "beyond the Great Eye of Orion" and returned, to walk like gods amongst men.
Despite the bleaching of semi-divine beings from modern consciousness, could it be possible, as the ancient texts insist, we are destined to "become as gods"? are the Mayan "Lords of Light" and the Egyptian/Tibetan "Shining Ones" really a higher form of human? According to many earth legends, such beings are supposed to return regularly, at the beginning and end of each time cycle, the 13,000 year half-point of our solar system's 26,000 year zodiacal orbit around galaxy centre. Because of conditions on our galactic orbit, these 13,000 year intervals or "worlds", seem to be separated by cataclysmic upheaval. According to the "calendar in stone" of the Great Pyramid, which describes the so-called "Phoenix Cycle" of our galactic orbit, the present time period ends (converted to our present calendar) in the year 2012 AD.
The Greek word PHOENIX, derived from the Egyptian word, PA-HANOK, actually means, "The House of Enoch". The Enochian knowledge suggests, these regular cataclysmic changes act as an evolutionary agent provocateur, to quicken the resident life forms to the next evolutionary phase, prior to exodus from the womb planet. Human evolution may proceed more rapidly than previously thought. The evidence now appearing, records civilisations before us, who mastered the physical continuum and progressed beyond this world. There were also those who failed.
We, too, have equal opportunity to make it or break it.The discoveries emerging from Egypt, describe the existence of a world wide pyramid temple system in prehistory, mounted like antennae on the key energy meridians, which were employed by ancient priest-scientists as a musical system to stabilize the tectonic plates of the planet... cataclysmic geology at it's finest.
>From the mother tongue word JEDAIAH, meaning "the way of the Word" or "the power of the Word", the ancient JEDAI priests used the language of Light to tune the planet like a giant harmonic bell. Much is being rediscovered in the last days of this time cycle. In the words of Dr. Jay Franz, of the Omega Foundation, "even if we don't dare to name it, there is a universal feeling of something impending on the world stage
Fish, any of approximately 34,000 species of vertebrate animals (phylum Chordata) found in the fresh and salt waters of the world. Living species range from the primitive jawless lampreys and hagfishes through the cartilaginous sharks, skates, and rays to the abundant and diverse bony fishes. Most fish species are cold-blooded; however, one species, the opah (Lampris guttatus), is warm-blooded.
The term fish is applied to a variety of vertebrates of several evolutionary lines. It describes a life-form rather than a taxonomic group. As members of the phylum Chordata, fish share certain features with other vertebrates. These features are gill slits at some point in the life cycle, a notochord, or skeletal supporting rod, a dorsal hollow nerve cord, and a tail. Living fishes represent some five classes, which are as distinct from one another as are the four classes of familiar air-breathing animals—amphibians, reptiles, birds, and mammals. For example, the jawless fishes (Agnatha) have gills in pouches and lack limb girdles. Extant agnathans are the lampreys and the hagfishes. As the name implies, the skeletons of fishes of the class Chondrichthyes (from chondr, “cartilage,” and ichthyes, “fish”) are made entirely of cartilage. Modern fish of this class lack a swim bladder, and their scales and teeth are made up of the same placoid material. Sharks, skates, and rays are examples of cartilaginous fishes. The bony fishes are by far the largest class. Examples range from the tiny seahorse to the 450-kg (1,000-pound) blue marlin, from the flattened soles and flounders to the boxy puffers and ocean sunfishes. Unlike the scales of the cartilaginous fishes, those of bony fishes, when present, grow throughout life and are made up of thin overlapping plates of bone. Bony fishes also have an operculum that covers the gill slits.
The study of fishes, the science of ichthyology, is of broad importance. Fishes are of interest to humans for many reasons, the most important being their relationship with and dependence on the environment. A more obvious reason for interest in fishes is their role as a moderate but important part of the world’s food supply. This resource, once thought unlimited, is now realized to be finite and in delicate balance with the biological, chemical, and physical factors of the aquatic environment. Overfishing, pollution, and alteration of the environment are the chief enemies of proper fisheries management, both in fresh waters and in the ocean. (For a detailed discussion of the technology and economics of fisheries, see commercial fishing.) Another practical reason for studying fishes is their use in disease control. As predators on mosquito larvae, they help curb malaria and other mosquito-borne diseases.
Fishes are valuable laboratory animals in many aspects of medical and biological research. For example, the readiness of many fishes to acclimate to captivity has allowed biologists to study behaviour, physiology, and even ecology under relatively natural conditions. Fishes have been especially important in the study of animal behaviour, where research on fishes has provided a broad base for the understanding of the more flexible behaviour of the higher vertebrates. The zebra fish is used as a model in studies of gene expression.
There are aesthetic and recreational reasons for an interest in fishes. Millions of people keep live fishes in home aquariums for the simple pleasure of observing the beauty and behaviour of animals otherwise unfamiliar to them. Aquarium fishes provide a personal challenge to many aquarists, allowing them to test their ability to keep a small section of the natural environment in their homes. Sportfishing is another way of enjoying the natural environment, also indulged in by millions of people every year. Interest in aquarium fishes and sportfishing supports multimillion-dollar industries throughout the world.
Fishes have been in existence for more than 450 million years, during which time they have evolved repeatedly to fit into almost every conceivable type of aquatic habitat. In a sense, land vertebrates are simply highly modified fishes: when fishes colonized the land habitat, they became tetrapod (four-legged) land vertebrates. The popular conception of a fish as a slippery, streamlined aquatic animal that possesses fins and breathes by gills applies to many fishes, but far more fishes deviate from that conception than conform to it. For example, the body is elongate in many forms and greatly shortened in others; the body is flattened in some (principally in bottom-dwelling fishes) and laterally compressed in many others; the fins may be elaborately extended, forming intricate shapes, or they may be reduced or even lost; and the positions of the mouth, eyes, nostrils, and gill openings vary widely. Air breathers have appeared in several evolutionary lines.
Many fishes are cryptically coloured and shaped, closely matching their respective environments; others are among the most brilliantly coloured of all organisms, with a wide range of hues, often of striking intensity, on a single individual. The brilliance of pigments may be enhanced by the surface structure of the fish, so that it almost seems to glow. A number of unrelated fishes have actual light-producing organs. Many fishes are able to alter their coloration—some for the purpose of camouflage, others for the enhancement of behavioral signals.
Fishes range in adult length from less than 10 mm (0.4 inch) to more than 20 metres (60 feet) and in weight from about 1.5 grams (less than 0.06 ounce) to many thousands of kilograms. Some live in shallow thermal springs at temperatures slightly above 42 °C (100 °F), others in cold Arctic seas a few degrees below 0 °C (32 °F) or in cold deep waters more than 4,000 metres (13,100 feet) beneath the ocean surface. The structural and, especially, the physiological adaptations for life at such extremes are relatively poorly known and provide the scientifically curious with great incentive for study.
Almost all natural bodies of water bear fish life, the exceptions being very hot thermal ponds and extremely salt-alkaline lakes, such as the Dead Sea in Asia and the Great Salt Lake in North America. The present distribution of fishes is a result of the geological history and development of Earth as well as the ability of fishes to undergo evolutionary change and to adapt to the available habitats. Fishes may be seen to be distributed according to habitat and according to geographical area. Major habitat differences are marine and freshwater. For the most part, the fishes in a marine habitat differ from those in a freshwater habitat, even in adjacent areas, but some, such as the salmon, migrate from one to the other. The freshwater habitats may be seen to be of many kinds. Fishes found in mountain torrents, Arctic lakes, tropical lakes, temperate streams, and tropical rivers will all differ from each other, both in obvious gross structure and in physiological attributes. Even in closely adjacent habitats where, for example, a tropical mountain torrent enters a lowland stream, the fish fauna will differ. The marine habitats can be divided into deep ocean floors (benthic), mid-water oceanic (bathypelagic), surface oceanic (pelagic), rocky coast, sandy coast, muddy shores, bays, estuaries, and others. Also, for example, rocky coastal shores in tropical and temperate regions will have different fish faunas, even when such habitats occur along the same coastline.
Although much is known about the present geographical distribution of fishes, far less is known about how that distribution came about. Many parts of the fish fauna of the fresh waters of North America and Eurasia are related and undoubtedly have a common origin. The faunas of Africa and South America are related, extremely old, and probably an expression of the drifting apart of the two continents. The fauna of southern Asia is related to that of Central Asia, and some of it appears to have entered Africa. The extremely large shore-fish faunas of the Indian and tropical Pacific oceans comprise a related complex, but the tropical shore fauna of the Atlantic, although containing Indo-Pacific components, is relatively limited and probably younger. The Arctic and Antarctic marine faunas are quite different from each other. The shore fauna of the North Pacific is quite distinct, and that of the North Atlantic more limited and probably younger. Pelagic oceanic fishes, especially those in deep waters, are similar the world over, showing little geographical isolation in terms of family groups. The deep oceanic habitat is very much the same throughout the world, but species differences do exist, showing geographical areas determined by oceanic currents and water masses.
All aspects of the life of a fish are closely correlated with adaptation to the total environment, physical, chemical, and biological. In studies, all the interdependent aspects of fish, such as behaviour, locomotion, reproduction, and physical and physiological characteristics, must be taken into account.
Correlated with their adaptation to an extremely wide variety of habitats is the extremely wide variety of life cycles that fishes display. The great majority hatch from relatively small eggs a few days to several weeks or more after the eggs are scattered in the water. Newly hatched young are still partially undeveloped and are called larvae until body structures such as fins, skeleton, and some organs are fully formed. Larval life is often very short, usually less than a few weeks, but it can be very long, some lampreys continuing as larvae for at least five years. Young and larval fishes, before reaching sexual maturity, must grow considerably, and their small size and other factors often dictate that they live in a habitat different than that of the adults. For example, most tropical marine shore fishes have pelagic larvae. Larval food also is different, and larval fishes often live in shallow waters, where they may be less exposed to predators.
After a fish reaches adult size, the length of its life is subject to many factors, such as innate rates of aging, predation pressure, and the nature of the local climate. The longevity of a species in the protected environment of an aquarium may have nothing to do with how long members of that species live in the wild. Many small fishes live only one to three years at the most. In some species, however, individuals may live as long as 10 or 20 or even 100 years.
Fish behaviour is a complicated and varied subject. As in almost all animals with a central nervous system, the nature of a response of an individual fish to stimuli from its environment depends upon the inherited characteristics of its nervous system, on what it has learned from past experience, and on the nature of the stimuli. Compared with the variety of human responses, however, that of a fish is stereotyped, not subject to much modification by “thought” or learning, and investigators must guard against anthropomorphic interpretations of fish behaviour.
Fishes perceive the world around them by the usual senses of sight, smell, hearing, touch, and taste and by special lateral line water-current detectors. In the few fishes that generate electric fields, a process that might best be called electrolocation aids in perception. One or another of these senses often is emphasized at the expense of others, depending upon the fish’s other adaptations. In fishes with large eyes, the sense of smell may be reduced; others, with small eyes, hunt and feed primarily by smell (such as some eels).
Specialized behaviour is primarily concerned with the three most important activities in the fish’s life: feeding, reproduction, and escape from enemies. Schooling behaviour of sardines on the high seas, for instance, is largely a protective device to avoid enemies, but it is also associated with and modified by their breeding and feeding requirements. Predatory fishes are often solitary, lying in wait to dart suddenly after their prey, a kind of locomotion impossible for beaked parrot fishes, which feed on coral, swimming in small groups from one coral head to the next. In addition, some predatory fishes that inhabit pelagic environments, such as tunas, often school.
Sleep in fishes, all of which lack true eyelids, consists of a seemingly listless state in which the fish maintains its balance but moves slowly. If attacked or disturbed, most can dart away. A few kinds of fishes lie on the bottom to sleep. Most catfishes, some loaches, and some eels and electric fishes are strictly nocturnal, being active and hunting for food during the night and retiring during the day to holes, thick vegetation, or other protective parts of the environment.
Communication between members of a species or between members of two or more species often is extremely important, especially in breeding behaviour (see below Reproduction). The mode of communication may be visual, as between the small so-called cleaner fish and a large fish of a very different species. The larger fish often allows the cleaner to enter its mouth to remove gill parasites. The cleaner is recognized by its distinctive colour and actions and therefore is not eaten, even if the larger fish is normally a predator. Communication is often chemical, signals being sent by specific chemicals called pheromones.
Many fishes have a streamlined body and swim freely in open water. Fish locomotion is closely correlated with habitat and ecological niche (the general position of the animal to its environment).
Many fishes in both marine and fresh waters swim at the surface and have mouths adapted to feed best (and sometimes only) at the surface. Often such fishes are long and slender, able to dart at surface insects or at other surface fishes and in turn to dart away from predators; needlefishes, halfbeaks, and topminnows (such as killifish and mosquito fish) are good examples. Oceanic flying fishes escape their predators by gathering speed above the water surface, with the lower lobe of the tail providing thrust in the water. They then glide hundreds of yards on enlarged, winglike pectoral and pelvic fins. South American freshwater flying fishes escape their enemies by jumping and propelling their strongly keeled bodies out of the water.
So-called mid-water swimmers, the most common type of fish, are of many kinds and live in many habitats. The powerful fusiform tunas and the trouts, for example, are adapted for strong, fast swimming, the tunas to capture prey speedily in the open ocean and the trouts to cope with the swift currents of streams and rivers. The trout body form is well adapted to many habitats. Fishes that live in relatively quiet waters such as bays or lake shores or slow rivers usually are not strong, fast swimmers but are capable of short, quick bursts of speed to escape a predator. Many of these fishes have their sides flattened, examples being the sunfish and the freshwater angelfish of aquarists. Fish associated with the bottom or substrate usually are slow swimmers. Open-water plankton-feeding fishes almost always remain fusiform and are capable of rapid, strong movement (for example, sardines and herrings of the open ocean and also many small minnows of streams and lakes).
Bottom-living fishes are of many kinds and have undergone many types of modification of their body shape and swimming habits. Rays, which evolved from strong-swimming mid-water sharks, usually stay close to the bottom and move by undulating their large pectoral fins. Flounders live in a similar habitat and move over the bottom by undulating the entire body. Many bottom fishes dart from place to place, resting on the bottom between movements, a motion common in gobies. One goby relative, the mudskipper, has taken to living at the edge of pools along the shore of muddy mangrove swamps. It escapes its enemies by flipping rapidly over the mud, out of the water. Some catfishes, synbranchid eels, the so-called climbing perch, and a few other fishes venture out over damp ground to find more promising waters than those that they left. They move by wriggling their bodies, sometimes using strong pectoral fins; most have accessory air-breathing organs. Many bottom-dwelling fishes live in mud holes or rocky crevices. Marine eels and gobies commonly are found in such habitats and for the most part venture far beyond their cavelike homes. Some bottom dwellers, such as the clingfishes (Gobiesocidae), have developed powerful adhesive disks that enable them to remain in place on the substrate in areas such as rocky coasts, where the action of the waves is great.
The methods of reproduction in fishes are varied, but most fishes lay a large number of small eggs, fertilized and scattered outside of the body. The eggs of pelagic fishes usually remain suspended in the open water. Many shore and freshwater fishes lay eggs on the bottom or among plants. Some have adhesive eggs. The mortality of the young and especially of the eggs is very high, and often only a few individuals grow to maturity out of hundreds, thousands, and in some cases millions of eggs laid.
Males produce sperm, usually as a milky white substance called milt, in two (sometimes one) testes within the body cavity. In bony fishes a sperm duct leads from each testis to a urogenital opening behind the vent or anus. In sharks and rays and in cyclostomes the duct leads to a cloaca. Sometimes the pelvic fins are modified to help transmit the milt to the eggs at the female’s vent or on the substrate where the female has placed them. Sometimes accessory organs are used to fertilize females internally—for example, the claspers of many sharks and rays.
In the females the eggs are formed in two ovaries (sometimes only one) and pass through the ovaries to the urogenital opening and to the outside. In some fishes the eggs are fertilized internally but are shed before development takes place. Members of about a dozen families each of bony fishes (teleosts) and sharks bear live young. Many skates and rays also bear live young. In some bony fishes the eggs simply develop within the female, the young emerging when the eggs hatch (ovoviviparous). Others develop within the ovary and are nourished by ovarian tissues after hatching (viviparous). There are also other methods utilized by fishes to nourish young within the female. In all live-bearers the young are born at a relatively large size and are few in number. In one family of primarily marine fishes, the surfperches from the Pacific coast of North America, Japan, and Korea, the males of at least one species are born sexually mature, although they are not fully grown.
Some fishes are hermaphroditic—an individual producing both sperm and eggs, usually at different stages of its life. Self-fertilization, however, is probably rare.
Successful reproduction and, in many cases, defense of the eggs and the young are assured by rather stereotypical but often elaborate courtship and parental behaviour, either by the male or the female or both. Some fishes prepare nests by hollowing out depressions in the sand bottom (cichlids, for example), build nests with plant materials and sticky threads excreted by the kidneys (sticklebacks), or blow a cluster of mucus-covered bubbles at the water surface (gouramis). The eggs are laid in these structures. Some varieties of cichlids and catfishes incubate eggs in their mouths.
Some fishes, such as salmon, undergo long migrations from the ocean and up large rivers to spawn in the gravel beds where they themselves hatched (anadromous fishes). Some, such as the freshwater eels (family Anguillidae), live and grow to maturity in fresh water and migrate to the sea to spawn (catadromous fishes). Other fishes undertake shorter migrations from lakes into streams, within the ocean, or enter spawning habitats that they do not ordinarily occupy in other ways.
The basic structure and function of the fish body are similar to those of all other vertebrates. The usual four types of tissues are present: surface or epithelial, connective (bone, cartilage, and fibrous tissues, as well as their derivative, blood), nerve, and muscle tissues. In addition, the fish’s organs and organ systems parallel those of other vertebrates.
The typical fish body is streamlined and spindle-shaped, with an anterior head, a gill apparatus, and a heart, the latter lying in the midline just below the gill chamber. The body cavity, containing the vital organs, is situated behind the head in the lower anterior part of the body. The anus usually marks the posterior termination of the body cavity and most often occurs just in front of the base of the anal fin. The spinal cord and vertebral column continue from the posterior part of the head to the base of the tail fin, passing dorsal to the body cavity and through the caudal (tail) region behind the body cavity. Most of the body is of muscular tissue, a high proportion of which is necessitated by swimming. In the course of evolution this basic body plan has been modified repeatedly into the many varieties of fish shapes that exist today.
The skeleton forms an integral part of the fish’s locomotion system, as well as serving to protect vital parts. The internal skeleton consists of the skull bones (except for the roofing bones of the head, which are really part of the external skeleton), the vertebral column, and the fin supports (fin rays). The fin supports are derived from the external skeleton but will be treated here because of their close functional relationship to the internal skeleton. The internal skeleton of cyclostomes, sharks, and rays is of cartilage; that of many fossil groups and some primitive living fishes is mostly of cartilage but may include some bone. In place of the vertebral column, the earliest vertebrates had a fully developed notochord, a flexible stiff rod of viscous cells surrounded by a strong fibrous sheath. During the evolution of modern fishes the rod was replaced in part by cartilage and then by ossified cartilage. Sharks and rays retain a cartilaginous vertebral column; bony fishes have spool-shaped vertebrae that in the more primitive living forms only partially replace the notochord. The skull, including the gill arches and jaws of bony fishes, is fully, or at least partially, ossified. That of sharks and rays remains cartilaginous, at times partially replaced by calcium deposits but never by true bone.
The supportive elements of the fins (basal or radial bones or both) have changed greatly during fish evolution. Some of these changes are described in the section below (Evolution and paleontology). Most fishes possess a single dorsal fin on the midline of the back. Many have two and a few have three dorsal fins. The other fins are the single tail and anal fins and paired pelvic and pectoral fins. A small fin, the adipose fin, with hairlike fin rays, occurs in many of the relatively primitive teleosts (such as trout) on the back near the base of the caudal fin.
The skin of a fish must serve many functions. It aids in maintaining the osmotic balance, provides physical protection for the body, is the site of coloration, contains sensory receptors, and, in some fishes, functions in respiration. Mucous glands, which aid in maintaining the water balance and offer protection from bacteria, are extremely numerous in fish skin, especially in cyclostomes and teleosts. Since mucous glands are present in the modern lampreys, it is reasonable to assume that they were present in primitive fishes, such as the ancient Silurian and Devonian agnathans. Protection from abrasion and predation is another function of the fish skin, and dermal (skin) bone arose early in fish evolution in response to this need. It is thought that bone first evolved in skin and only later invaded the cartilaginous areas of the fish’s body, to provide additional support and protection. There is some argument as to which came first, cartilage or bone, and fossil evidence does not settle the question. In any event, dermal bone has played an important part in fish evolution and has different characteristics in different groups of fishes. Several groups are characterized at least in part by the kind of bony scales they possess.
Scales have played an important part in the evolution of fishes. Primitive fishes usually had thick bony plates or thick scales in several layers of bone, enamel, and related substances. Modern teleost fishes have scales of bone, which, while still protective, allow much more freedom of motion in the body. A few modern teleosts (some catfishes, sticklebacks, and others) have secondarily acquired bony plates in the skin. Modern and early sharks possessed placoid scales, a relatively primitive type of scale with a toothlike structure, consisting of an outside layer of enamel-like substance (vitrodentine), an inner layer of dentine, and a pulp cavity containing nerves and blood vessels. Primitive bony fishes had thick scales of either the ganoid or the cosmoid type. Cosmoid scales have a hard, enamel-like outer layer, an inner layer of cosmine (a form of dentine), and then a layer of vascular bone (isopedine). In ganoid scales the hard outer layer is different chemically and is called ganoin. Under this is a cosminelike layer and then a vascular bony layer. The thin, translucent bony scales of modern fishes, called cycloid and ctenoid (the latter distinguished by serrations at the edges), lack enameloid and dentine layers.
Skin has several other functions in fishes. It is well supplied with nerve endings and presumably receives tactile, thermal, and pain stimuli. Skin is also well supplied with blood vessels. Some fishes breathe in part through the skin, by the exchange of oxygen and carbon dioxide between the surrounding water and numerous small blood vessels near the skin surface.
Skin serves as protection through the control of coloration. Fishes exhibit an almost limitless range of colours. The colours often blend closely with the surroundings, effectively hiding the animal. Many fishes use bright colours for territorial advertisement or as recognition marks for other members of their own species, or sometimes for members of other species. Many fishes can change their colour to a greater or lesser degree, by movement of pigment within the pigment cells (chromatophores). Black pigment cells (melanophores), of almost universal occurrence in fishes, are often juxtaposed with other pigment cells. When placed beneath iridocytes or leucophores (bearing the silvery or white pigment guanine), melanophores produce structural colours of blue and green. These colours are often extremely intense, because they are formed by refraction of light through the needlelike crystals of guanine. The blue and green refracted colours are often relatively pure, lacking the red and yellow rays, which have been absorbed by the black pigment (melanin) of the melanophores. Yellow, orange, and red colours are produced by erythrophores, cells containing the appropriate carotenoid pigments. Other colours are produced by combinations of melanophores, erythrophores, and iridocytes.
The major portion of the body of most fishes consists of muscles. Most of the mass is trunk musculature, the fin muscles usually being relatively small. The caudal fin is usually the most powerful fin, being moved by the trunk musculature. The body musculature is usually arranged in rows of chevron-shaped segments on each side. Contractions of these segments, each attached to adjacent vertebrae and vertebral processes, bends the body on the vertebral joint, producing successive undulations of the body, passing from the head to the tail, and producing driving strokes of the tail. It is the latter that provides the strong forward movement for most fishes.
The digestive system, in a functional sense, starts at the mouth, with the teeth used to capture prey or collect plant foods. Mouth shape and tooth structure vary greatly in fishes, depending on the kind of food normally eaten. Most fishes are predacious, feeding on small invertebrates or other fishes and have simple conical teeth on the jaws, on at least some of the bones of the roof of the mouth, and on special gill arch structures just in front of the esophagus. The latter are throat teeth. Most predacious fishes swallow their prey whole, and the teeth are used for grasping and holding prey, for orienting prey to be swallowed (head first) and for working the prey toward the esophagus. There are a variety of tooth types in fishes. Some fishes, such as sharks and piranhas, have cutting teeth for biting chunks out of their victims. A shark’s tooth, although superficially like that of a piranha, appears in many respects to be a modified scale, while that of the piranha is like that of other bony fishes, consisting of dentine and enamel. Parrot fishes have beaklike mouths with short incisor-like teeth for breaking off coral and have heavy pavementlike throat teeth for crushing the coral. Some catfishes have small brushlike teeth, arranged in rows on the jaws, for scraping plant and animal growth from rocks. Many fishes (such as the Cyprinidae or minnows) have no jaw teeth at all but have very strong throat teeth.
Some fishes gather planktonic food by straining it from their gill cavities with numerous elongate stiff rods (gill rakers) anchored by one end to the gill bars. The food collected on these rods is passed to the throat, where it is swallowed. Most fishes have only short gill rakers that help keep food particles from escaping out the mouth cavity into the gill chamber.
Once reaching the throat, food enters a short, often greatly distensible esophagus, a simple tube with a muscular wall leading into a stomach. The stomach varies greatly in fishes, depending upon the diet. In most predacious fishes it is a simple straight or curved tube or pouch with a muscular wall and a glandular lining. Food is largely digested there and leaves the stomach in liquid form.
Between the stomach and the intestine, ducts enter the digestive tube from the liver and pancreas. The liver is a large, clearly defined organ. The pancreas may be embedded in it, diffused through it, or broken into small parts spread along some of the intestine. The junction between the stomach and the intestine is marked by a muscular valve. Pyloric ceca (blind sacs) occur in some fishes at this junction and have a digestive or absorptive function or both.
The intestine itself is quite variable in length, depending upon the fish’s diet. It is short in predacious forms, sometimes no longer than the body cavity, but long in herbivorous forms, being coiled and several times longer than the entire length of the fish in some species of South American catfishes. The intestine is primarily an organ for absorbing nutrients into the bloodstream. The larger its internal surface, the greater its absorptive efficiency, and a spiral valve is one method of increasing its absorption surface.
Sharks, rays, chimaeras, lungfishes, surviving chondrosteans, holosteans, and even a few of the more primitive teleosts have a spiral valve or at least traces of it in the intestine. Most modern teleosts have increased the area of the intestinal walls by having numerous folds and villi (fingerlike projections) somewhat like those in humans. Undigested substances are passed to the exterior through the anus in most teleost fishes. In lungfishes, sharks, and rays, it is first passed through the cloaca, a common cavity receiving the intestinal opening and the ducts from the urogenital system.
Oxygen and carbon dioxide dissolve in water, and most fishes exchange dissolved oxygen and carbon dioxide in water by means of the gills. The gills lie behind and to the side of the mouth cavity and consist of fleshy filaments supported by the gill arches and filled with blood vessels, which give gills a bright red colour. Water taken in continuously through the mouth passes backward between the gill bars and over the gill filaments, where the exchange of gases takes place. The gills are protected by a gill cover in teleosts and many other fishes but by flaps of skin in sharks, rays, and some of the older fossil fish groups. The blood capillaries in the gill filaments are close to the gill surface to take up oxygen from the water and to give up excess carbon dioxide to the water.
Most modern fishes have a hydrostatic (ballast) organ, called the swim bladder, that lies in the body cavity just below the kidney and above the stomach and intestine. It originated as a diverticulum of the digestive canal. In advanced teleosts, especially the acanthopterygians, the bladder has lost its connection with the digestive tract, a condition called physoclistic. The connection has been retained (physostomous) by many relatively primitive teleosts. In several unrelated lines of fishes, the bladder has become specialized as a lung or, at least, as a highly vascularized accessory breathing organ. Some fishes with such accessory organs are obligate air breathers and will drown if denied access to the surface, even in well-oxygenated water. Fishes with a hydrostatic form of swim bladder can control their depth by regulating the amount of gas in the bladder. The gas, mostly oxygen, is secreted into the bladder by special glands, rendering the fish more buoyant; the gas is absorbed into the bloodstream by another special organ, reducing the overall buoyancy and allowing the fish to sink. Some deep-sea fishes may have oils, rather than gas, in the bladder. Other deep-sea and some bottom-living forms have much-reduced swim bladders or have lost the organ entirely.
The swim bladder of fishes follows the same developmental pattern as the lungs of land vertebrates. There is no doubt that the two structures have the same historical origin in primitive fishes. More or less intermediate forms still survive among the more primitive types of fishes, such as the lungfishes Lepidosiren and Protopterus.
The circulatory, or blood vascular, system consists of the heart, the arteries, the capillaries, and the veins. It is in the capillaries that the interchange of oxygen, carbon dioxide, nutrients, and other substances such as hormones and waste products takes place. The capillaries lead to the veins, which return the venous blood with its waste products to the heart, kidneys, and gills. There are two kinds of capillary beds: those in the gills and those in the rest of the body. The heart, a folded continuous muscular tube with three or four saclike enlargements, undergoes rhythmic contractions and receives venous blood in a sinus venosus. It passes the blood to an auricle and then into a thick muscular pump, the ventricle. From the ventricle the blood goes to a bulbous structure at the base of a ventral aorta just below the gills. The blood passes to the afferent (receiving) arteries of the gill arches and then to the gill capillaries. There waste gases are given off to the environment, and oxygen is absorbed. The oxygenated blood enters efferent (exuant) arteries of the gill arches and then flows into the dorsal aorta. From there blood is distributed to the tissues and organs of the body. One-way valves prevent backflow. The circulation of fishes thus differs from that of the reptiles, birds, and mammals in that oxygenated blood is not returned to the heart prior to distribution to the other parts of the body.
The primary excretory organ in fishes, as in other vertebrates, is the kidney. In fishes some excretion also takes place in the digestive tract, skin, and especially the gills (where ammonia is given off). Compared with land vertebrates, fishes have a special problem in maintaining their internal environment at a constant concentration of water and dissolved substances, such as salts. Proper balance of the internal environment (homeostasis) of a fish is in a great part maintained by the excretory system, especially the kidney.
The kidney, gills, and skin play an important role in maintaining a fish’s internal environment and checking the effects of osmosis. Marine fishes live in an environment in which the water around them has a greater concentration of salts than they can have inside their body and still maintain life. Freshwater fishes, on the other hand, live in water with a much lower concentration of salts than they require inside their bodies. Osmosis tends to promote the loss of water from the body of a marine fish and absorption of water by that of a freshwater fish. Mucus in the skin tends to slow the process but is not a sufficient barrier to prevent the movement of fluids through the permeable skin. When solutions on two sides of a permeable membrane have different concentrations of dissolved substances, water will pass through the membrane into the more concentrated solution, while the dissolved chemicals move into the area of lower concentration (diffusion).
The kidney of freshwater fishes is often larger in relation to body weight than that of marine fishes. In both groups the kidney excretes wastes from the body, but the kidney of freshwater fishes also excretes large amounts of water, counteracting the water absorbed through the skin. Freshwater fishes tend to lose salt to the environment and must replace it. They get some salt from their food, but the gills and skin inside the mouth actively absorb salt from water passed through the mouth. This absorption is performed by special cells capable of moving salts against the diffusion gradient. Freshwater fishes drink very little water and take in little water with their food.
Marine fishes must conserve water, and therefore their kidneys excrete little water. To maintain their water balance, marine fishes drink large quantities of seawater, retaining most of the water and excreting the salt. Most nitrogenous waste in marine fishes appears to be secreted by the gills as ammonia. Marine fishes can excrete salt by clusters of special cells (chloride cells) in the gills.
There are several teleosts—for example, the salmon—that travel between fresh water and seawater and must adjust to the reversal of osmotic gradients. They adjust their physiological processes by spending time (often surprisingly little time) in the intermediate brackish environment.
Marine hagfishes, sharks, and rays have osmotic concentrations in their blood about equal to that of seawater and so do not have to drink water nor perform much physiological work to maintain their osmotic balance. In sharks and rays the osmotic concentration is kept high by retention of urea in the blood. Freshwater sharks have a lowered concentration of urea in the blood.
Endocrine glands secrete their products into the bloodstream and body tissues and, along with the central nervous system, control and regulate many kinds of body functions. Cyclostomes have a well-developed endocrine system, and presumably it was well developed in the early Agnatha, ancestral to modern fishes. Although the endocrine system in fishes is similar to that of higher vertebrates, there are numerous differences in detail. The pituitary, the thyroid, the suprarenals, the adrenals, the pancreatic islets, the sex glands (ovaries and testes), the inner wall of the intestine, and the bodies of the ultimobranchial gland make up the endocrine system in fishes. There are some others whose function is not well understood. These organs regulate sexual activity and reproduction, growth, osmotic pressure, general metabolic activities such as the storage of fat and the utilization of foodstuffs, blood pressure, and certain aspects of skin colour. Many of these activities are also controlled in part by the central nervous system, which works with the endocrine system in maintaining the life of a fish. Some parts of the endocrine system are developmentally, and undoubtedly evolutionarily, derived from the nervous system.
As in all vertebrates, the nervous system of fishes is the primary mechanism coordinating body activities, as well as integrating these activities in the appropriate manner with stimuli from the environment. The central nervous system, consisting of the brain and spinal cord, is the primary integrating mechanism. The peripheral nervous system, consisting of nerves that connect the brain and spinal cord to various body organs, carries sensory information from special receptor organs such as the eyes, internal ears, nares (sense of smell), taste glands, and others to the integrating centres of the brain and spinal cord. The peripheral nervous system also carries information via different nerve cells from the integrating centres of the brain and spinal cord. This coded information is carried to the various organs and body systems, such as the skeletal muscular system, for appropriate action in response to the original external or internal stimulus. Another branch of the nervous system, the autonomic nervous system, helps to coordinate the activities of many glands and organs and is itself closely connected to the integrating centres of the brain.
The brain of the fish is divided into several anatomical and functional parts, all closely interconnected but each serving as the primary centre of integrating particular kinds of responses and activities. Several of these centres or parts are primarily associated with one type of sensory perception, such as sight, hearing, or smell (olfaction).
The sense of smell is important in almost all fishes. Certain eels with tiny eyes depend mostly on smell for location of food. The olfactory, or nasal, organ of fishes is located on the dorsal surface of the snout. The lining of the nasal organ has special sensory cells that perceive chemicals dissolved in the water, such as substances from food material, and send sensory information to the brain by way of the first cranial nerve. Odour also serves as an alarm system. Many fishes, especially various species of freshwater minnows, react with alarm to a chemical released from the skin of an injured member of their own species.
Many fishes have a well-developed sense of taste, and tiny pitlike taste buds or organs are located not only within their mouth cavities but also over their heads and parts of their body. Catfishes, which often have poor vision, have barbels (“whiskers”) that serve as supplementary taste organs, those around the mouth being actively used to search out food on the bottom. Some species of naturally blind cave fishes are especially well supplied with taste buds, which often cover most of their body surface.
Sight is extremely important in most fishes. The eye of a fish is basically like that of all other vertebrates, but the eyes of fishes are extremely varied in structure and adaptation. In general, fishes living in dark and dim water habitats have large eyes, unless they have specialized in some compensatory way so that another sense (such as smell) is dominant, in which case the eyes will often be reduced. Fishes living in brightly lighted shallow waters often will have relatively small but efficient eyes. Cyclostomes have somewhat less elaborate eyes than other fishes, with skin stretched over the eyeball perhaps making their vision somewhat less effective. Most fishes have a spherical lens and accommodate their vision to far or near subjects by moving the lens within the eyeball. A few sharks accommodate by changing the shape of the lens, as in land vertebrates. Those fishes that are heavily dependent upon the eyes have especially strong muscles for accommodation. Most fishes see well, despite the restrictions imposed by frequent turbidity of the water and by light refraction.
Fossil evidence suggests that colour vision evolved in fishes more than 300 million years ago, but not all living fishes have retained this ability. Experimental evidence indicates that many shallow-water fishes, if not all, have colour vision and see some colours especially well, but some bottom-dwelling shore fishes live in areas where the water is sufficiently deep to filter out most if not all colours, and these fishes apparently never see colours. When tested in shallow water, they apparently are unable to respond to colour differences.
Sound perception and balance are intimately associated senses in a fish. The organs of hearing are entirely internal, located within the skull, on each side of the brain and somewhat behind the eyes. Sound waves, especially those of low frequencies, travel readily through water and impinge directly upon the bones and fluids of the head and body, to be transmitted to the hearing organs. Fishes readily respond to sound; for example, a trout conditioned to escape by the approach of fishermen will take flight upon perceiving footsteps on a stream bank even if it cannot see a fisherman. Compared with humans, however, the range of sound frequencies heard by fishes is greatly restricted. Many fishes communicate with each other by producing sounds in their swim bladders, in their throats by rasping their teeth, and in other ways.
A fish or other vertebrate seldom has to rely on a single type of sensory information to determine the nature of the environment around it. A catfish uses taste and touch when examining a food object with its oral barbels. Like most other animals, fishes have many touch receptors over their body surface. Pain and temperature receptors also are present in fishes and presumably produce the same kind of information to a fish as to humans. Fishes react in a negative fashion to stimuli that would be painful to human beings, suggesting that they feel a sensation of pain.
An important sensory system in fishes that is absent in other vertebrates (except some amphibians) is the lateral line system. This consists of a series of heavily innervated small canals located in the skin and bone around the eyes, along the lower jaw, over the head, and down the mid-side of the body, where it is associated with the scales. Intermittently along these canals are located tiny sensory organs (pit organs) that apparently detect changes in pressure. The system allows a fish to sense changes in water currents and pressure, thereby helping the fish to orient itself to the various changes that occur in the physical environment.
The project presented by Taller 301 (CO), LOLA Landscape Architects (NL), L+CC (NL) and a-Zone (RU) has been awarded third prize and as competition winners will be involved in the future development of the park.
Image: Greenhouse
Ant Theme: Research by Dr. Jonathan Klassen
Research in the Klassen lab tries to understand how symbioses (“organisms living together”) function as a unit, despite being made up of different individuals that have different ecologies and evolutionary interests. This research is important because of how widespread such symbioses are in nature, e.g., between humans and their gut microbes, or plants and microbes surrounding their roots in the rhizosphere. However, the complexity of such systems makes them difficult to study. Instead, we study a fungus-growing ant, Trachymyrmex septentrionalis, as a model system where we can understand the precise function of each symbiont and how it interacts with the others. T. septentrionalis is the northernmost fungus growing ant, and is abundant in pine flat forests throughout the Eastern USA, ranging as far north as Long Island, New York. In this symbiosis, T. septentrionalis ants collect plant material and insect feces, which they feed to a specific “cultivar” fungus that they farm in underground gardens. Once the fungus has digested this food, it forms nutrient-rich swellings that the ants feed upon. The ants also protect their cultivar fungus from disease using antibiotic-producing Pseudonocardia bacteria that reside on the ants’ proplueral plates (i.e., “chest”). The ants therefore both farm the cultivar fungus as their food source and protect it by “crop spraying” antibiotics produced by their symbiotic Pseudonocardia bacteria.
In this collaboration, we used macrophotography to visualize the various members of our symbiosis and the interactions between them. We took images of each life cycle stage of the ant, and observed how their bodies developed as they moved first from larvae, to pupae, and finally to fully developed adult workers and the male reproductive caste. We also imaged the underside of a worker adult, which showed how the Pseudonocardia bacteria form an ordered array of white microcolonies covering the ant’s propleural plate. These colonies likely relate to an array of glands on the ant’s body that as thought to feed each colony of bacteria. Finally we also imaged the cultivar fungus to investigate how its structure related to its relationship with the ants. Interestingly, our images revealed patches of necrotic cultivar tissue, perhaps indicating the presence of a melanin-based immune system in this fungus. This has never been observed before, and whether it is caused by the ant or some other factor remains unknown. Together, these macrophotographic images allowed us to view our ants and their symbionts in unprecedented detail, and demonstrates the intimacy of the interactions that occur between them.
EXHIBIT ON DISPLAY NOW AT UCONN'S NATURAL HISTORY MUSEUM
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Images in this gallery were captured by:
Mark Smith M.S. Geoscientist mark@macroscopicsolutions.com
Annette Evans Ph.D. Student at the University of Connecticut annette@macroscopicsolutions.com
The Chieftain was a radical evolutionary development of the successful Centurion line of tanks that had emerged at the end of WWII. The British had learned during the war that their tanks often lacked sufficient protection and firepower compared to those fielded by the enemy, and that this had led to high casualty levels when faced with the superior German tanks. Leyland, who had been involved in Centurion, had built their own prototypes of a new tank design in 1956, and these led to a War Office specification for a new tank. The design was accepted in the early 1960s.
Chieftain was designed to be as well protected as possible and to be equipped with a powerful rifled cannon. The heavy armour came at the price of reduced mobility, chiefly due to engine power limitations, which was perhaps the Chieftain's main drawback. The design included a heavily sloped hull and turret which greatly increased the effective thickness of the frontal armour - 388mm on the glacis (from an actual thickness of 120mm), and 390mm on the turret (from 195mm).
It had a mantleless turret, in order to take full advantage of reclining the vehicle up to 10° in a hull-down position. The driver lay semi-recumbent in the hull when his hatch was closed down which helped to reduce overall height. The commander, gunner and loader were situated in the turret. To the left side of the turret was a large IR searchlight in an armoured housing. The suspension was of the Horstmann bogie type, with large side plates to protect the tracks and provide stand-off protection from hollow charge attack.
The main armament was the 120mm L11A5 rifled gun. This differed from most contemporary main tank armament as it used projectiles and charges which were loaded separately, as opposed to a single fixed round. The charges were encased in combustible bags which were stored in 36 recesses surrounded by water jackets. In the event of a hit which penetrated the fighting compartment, the water jacket would rupture, soaking the charges and preventing a catastrophic ammunition explosion. The gun itself could fire a wide range of ammunition, but the most commonly loaded types were HESH (high-explosive squash head) or APDS (armour-piercing discarding sabot), or practice round equivalents for both types.
When first introduced, a 12.7mm ranging machine-gun was mounted above the main gun. Later, in the late 1970s and early 1980s, a Barr and Stroud laser rangefinder replaced it. This allowed engagements at much longer ranges, and also could be linked to the fire-control system, allowing more rapid engagements and changes of target. The gun was fully stabilised with a fully computerised integrated control system. The secondary armament consisted of a coaxial L8A1 7.62mm machine gun, and another 7.62mm machine gun mounted on the commander's cupola.
Like its European competitors, the Chieftain found a large export market in the Middle East, but unlike the earlier Centurion, it was not adopted by any other NATO or Commonwealth countries.