Flint Hills
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The Great Horned Owl – large, powerful, and long-lived – is adapted by its anatomy, physiology, and behavior to survive in any climate but arctic-alpine regions. Equally at home in desert, grassland, suburban, and forest habitats, north to the tree line, it has a diverse prey base and the most extensive range with the most variation in nesting sites of any American owl. This one was at Macuquinho Lodge and was a real treat to see it during the day!
Have a Peaceful weekend!
Thanks a lot for your visits, comments, faves, invites, etc. Very much appreciated!
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Member of Nature’s Spirit
Good Stewards of Nature
Great Horned Owl (Jacurutu in Portuguese) – is a large, powerful, and long-lived – is adapted by its anatomy, physiology, and behavior to survive in any climate but arctic-alpine regions. Equally at home in desert, grassland, suburban, and forest habitats, north to the tree line, it has a diverse prey base and the most extensive range with the most variation in nesting sites of any American owl.
Its large eyes are equipped with many rods for night vision and pupils that open widely in the dark. Although its eyes do not move, flexibility in the atlanto-occipital joint enables this owl to swivel its head more than 180° and to look in any direction. Its hearing is acute, assisted by facial disc feathers that direct sound waves to its ears. Its feathers are exceptionally soft, providing superb insulation and allowing for silent flight. Females are able to maintain their eggs at incubating temperature near 37 °C, even when the ambient temperature is more than 70° colder. This species is a perch-and-pounce hunter. Although its short, wide wings allow maneuverability among trees of the forest, the resulting high wing-loading makes aerial foraging less efficient. Its strong talons, which take a force of 13 kg to open, allow it to sever the spinal column of prey even larger than itself. Its hooked beak efficiently tears meat from bones.
www.eagles.org/international-owl-awareness-day/
Thanks a lot for your visits, comments, faves, invites, etc. Very much appreciated!
© All my images are protected under international authors copyright laws and may not be downloaded, reproduced, copied, transmitted or manipulated without my written explicit permission. All rights reserved. Please contact me at thelma.gatuzzo@gmail.com if you intend to buy or use any of my images.
My instagram if you like: @thelmag and @thelma_and_cats
Amsterdam - Valeriusplein.
Op de hoek van De Lairessestraat en het Valeriusplein, werd in 1917 het Physiologisch Laboratorium geopend. Na de Valeriuskliniek, die in 1910 was geopend, was dit de tweede poot van de Medische Faculteit in oprichting. Het gebouw werd in Amsterdamse Schoolstijl ontworpen door de architecten Th. Groenendijk en Th. J. Lammers (amsterdamse-school.nl).
DDD / TDD.
© Leanne Boulton, All Rights Reserved
Some kind of landscape photography I think. Captured in April 2023 at Troon South Beach, Scotland.
There are 3 vital things that someone with severe CPTSD needs in order to function and heal.
1/ Consistency, predictability and routine.
2/ A place of safety and comfort
3/ Patience and compassion
Without these my trauma response is activated. I can't help that, it is physiological.
These needs have not been fully met for the past 2 years or so. Is it any wonder my symptoms have worsened? Now I am blamed for not healing fast enough. 25 years of abuse and PTSD cannot be fixed with 1 year of therapy and just one year of healing afterwards, least of all when those needs are not fully met. I didn't stand a chance.
Last night a friend from the past messaged me at a critical time. They chatted with me online for some 2 hours or more. They actually made me cry, smile and even laugh. It saved The Samaritans a call and that friend may have saved my life. The timing was impeccable.
The biggest threat to me is not having the 3 vital things. Without those I will spiral into hell. There is no chance I can heal without them. I just don't know where I can get them now. I can't do this alone and I will need actual in-person physical help as well. At my worst I am unable to even cook a meal or even answer the door. At times I could not even leave the house into the garden.
At my best there are little nuggets of the old 'Leanne' there. I just can't find her by myself. I am too ill to do it all alone now.
For the friend that contacted me last night. I am in their debt.
I am trying to post to Flickr and enjoy your photography to maintain routine. It has helped to hold me together for a long time. I am struggling to comment on other people's work or find 'happy' photographs to share. I hope I can get back there though.
In the meantime. Thank you for your understanding and caring. However remote, it does help. It does help.
The domestic yak (Bos grunniens) is a long-haired domesticated bovid found throughout the Himalayan region of the Indian subcontinent, the Tibetan Plateau and as far north as Mongolia and Russia. It is descended from the wild yak (Bos mutus).
The English word "yak" is a loan originating from Tibetan: གཡག་, Wylie: g.yag. In Tibetan, it refers only to the male of the species, the female being called Tibetan: འབྲི་, Wylie: 'bri, or nak. In English, as in most other languages that have borrowed the word, "yak" is usually used for both sexes.
Physiology
Yak physiology is well adapted to high altitudes, having larger lungs and heart than cattle found at lower altitudes, as well as greater capacity for transporting oxygen through their blood due to the persistence of foetal haemoglobin throughout life. Conversely, yaks do not thrive at lower altitudes, and begin to suffer from heat exhaustion above about 15 °C (59 °F). Further adaptations to the cold include a thick layer of subcutaneous fat, and an almost complete lack of functional sweat glands.
“Another head hangs lowly
Child is slowly taken
And the violence, caused such silence
Who are we mistaken?
But you see, it’s not me
It’s not my family
In your head , in your head they are fighting”
Zombie By the Cranberries
I was going to attach the audio of an Air Force or National Guard Jet, diving at our Motorhome. But, I like this picture to much to have a play icon, stuck in the middle of it. I’ll post the audio, to another post. It is one of the many, many acts, I’ve caught on audio. This is our government using its Military; to stalk, harass, intimidate and bait, a US Citizen, on US Soil. There are thousands of Targeted Individuals, in the United States. These American Whistleblowers, Targets, are being used as Test Subjects. For Physiological and Electronic Torture. 60 Minutes (CBS), did a Segment on this; Episode 23, aired 2-20-22, Americans Targeted. I commend them on their efforts to expose this.
In this Segment; American victims, described these Electronic Attacks. Some at our Capitol. They and their family members acquired, devastating medical conditions from these attacks. One government official; described the attacks on his children, while they were sleeping. He said they would toss, turn, there would be a loud noise admitting around their heads. Once removed from the area; they stopped. They suffered from numerous medical conditions. He said he wished our Government would stop Gaslighting, and do something.
Another woman, describing how her child went blind in the right eye. If you have the time, I encourage you to educate yourself on what is really happening in America. You will need a Paramount +, subscription, to stream 60 Minutes that far back. It’s your America, It's worth watching.
During the segment; our own CIA Director, said he doesn’t know who or how they are doing it. I call Bullshit! Mr. CIA Director, if you want to know about Electronic Torture, come see me; Rick Pineiro, now in Grand Junction, Colorado, area. These people have no boundaries. I have 14 years of Targeted experience. It’s pretty much the same Bullshit with our FBI Director, Homeland Security Director and Justice Department. It doesn’t matter what administration is in power. Our Government and many legislators are beyond corrupt. They are what have gotten us here today. Power and Control.
As America continues to astonish the world with its barbaric behavior. Our Government continues to release and duplicate its Zombies, in our communities. These aren’t real Zombies, but are the bottom feeders, the village idiots, sociopaths and self anointed narcissus. They live in every American Community. These are Americans; laying in wait for the next Target to come to their community. Yep, the Boogieman is here, they have no rights, this is America. Their goal is to rid their communities of anyone, they feel not worthy, of living within their communities. Kinda reminds you of the KKK. Guided by Contractors and Branches of our Government; these people have no boundaries, no accountability. And, this is why many local law enforcement agencies, turn a blind eye, or, participate. Kinda reminds me of the KKK, again. I read about them, but not in our schools.
These Americans will use local law enforcement, children, animals, pets, guns, vehicles, Physiological and Electronic Torture. They will destroy your life. They will bait you, discredit you, rally a community against you. Mob you, stalk you, harass you, illegally watch, video and record everything in your life. They and government contractors will use Physiological and Electronic Torture. They will use these tactics; Gaslighting, perform Street Theater, and Baiting you. At VA Clinics, Hospitals and other Medical Facilities. This is what you call Gang Stalking in America. I call it Domestic Terrorism. Our Homeland Security Secretary, wants to increase this type of community hate. He wants more Community Involved Monitoring. These people allowed roaming free across America, without consequence for their actions.
As I composed these 5 images, I took for this picture; someone very close started firing off riffle rounds. Bullets, whizzing not far overhead. When I set up to take pictures this morning (7-6-22), someone starts firing a high-powered rifle in the background. When I stepped out of our Motorhome today, to move our solar panels; someone started shooting a high-powered rifle over our Motorhome. Rounds whizzing over it, as I moved the panels. Koda, inside barking. Then they started firing rounds, into the hill I was taking pictures from this morning. It was just to the front of our camp.
Mr. Homeland Security, CIA and FBI Directors. This happens in Colorado (where I currently am), Wyoming, Arizona and Utah. When I was in the Military, I expected live rounds, aircraft diving overhead; I lived it. I didn’t expect it across, state by state; in the United States of America. This is what happens to brave Americans; trying to expose the truth about Corruption, Electronic Torture and Gang Stalking. It would be great if one of you Directors, would grab your balls, and find a grain of that type of courage!
Until we remove ourselves of our corrupt officials, it will only get worse. Many years ago; I predicted mobbing would eventually get to the point; where Law Enforcement could not control these mobs. Just look through my photostream. Here we are, folks. Aren't you proud! Now I’m going to have Billy-Bob, and his Sister’s Daughter Wife, chase me down in a big pickup truck. Brandishing oversized, American flags in the bed. Go American Education System; showing yourself so vividly.
This photo and all in my photostream are free to download, print, and share. All I ask is you keep my Trade Marks and share something with someone in need. Maybe a couple bottles of water, or a sandwich. You would be surprised how much people do have in common.
I’ve rambled on long enough for today. Violence is not the answer, please educate yourself.
Thanks for visiting our photostream.
Il Morimo scabroso è un grosso Cerambice (35 mm) di colore grigio nero con alcune macchie più scure sulle elitre e due spine sul corsaletto. Comune in tutta l'Italia, depone le uova sui tronchi di noci , pioppi e querce. Le larve, scavando gallerie nel legno, causano alle piante danni fisiologici e tecnologici. L'esemplare femmina della foto con le antenne aperte misurava circa 10 cm di larghezza.
The Morimus asper is a large beetle (35 mm) of black-gray color with some darker spots on the elytra and two spines on the breastplate. Common throughout Italy, lays its eggs on the trunks of walnuts, poplars and oaks. The larvae dig tunnels into the wood causing physiological damage to plants and technology.The female specimen in photos with open antennas measured about 10 cm wide.
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All of my photographs are Copyright ©Marco Ottaviani, All Rights Reserved. If you wish to use any of them, please contact me.
Fliying while feeding the baby. Anna's Hummingbird. California.
All birds are fascinating creatures, but there are many facts about hummingbirds that make them astonishing to even experienced birders. From physiological facts to lifestyle facts to distribution facts, hummingbirds are some of the most interesting of the nearly 10,000 bird species in the world.
There are more than 325 hummingbird species in the world. Only 8 species regularly breed in the United States, though up to two dozen species may visit the country.
Hummingbirds cannot walk or hop, though their feet can be used to scoot sideways while they are perched.
Hummingbirds have 1,000-1,500 feathers, the fewest number of feathers of any bird species in the world.
A hummingbird’s wings beat between 50 and 200 flaps per second depending on the direction of flight and air conditions.
A hummingbird’s maximum forward flight speed is 30 miles per hour, though the birds can reach up to 60 miles per hour in a dive.
An average hummingbird’s heart rate is more than 1,200 beats per minute.
At rest, a hummingbird takes an average of 250 breaths per minute.
At Transcend Health – an exercise physiologist newcastle, we are about inspiring and helping you to move your body, and experience life unrestrained by pain, injury, disease and illness.
The whale shark, Rhincodon typus, is a slow-moving filter feeding shark and the largest extant fish species. The largest confirmed individual had a length of 12.65 metres (41.50 ft) and a weight of more than 21.5 tonnes (47,000 lb), and there are unconfirmed reports of considerably larger whale sharks. This distinctively-marked fish is the only member of its genus Rhincodon and its family, Rhincodontidae (called Rhiniodon and Rhinodontidae before 1984), which belongs to the subclass Elasmobranchii in the class Chondrichthyes. The species originated about 60 million years ago.
The whale shark is found in tropical and warm oceans and lives in the open sea with a lifespan of about 70 years.[3] Although whale sharks have very large mouths, as filter feeders they feed mainly, though not exclusively, on plankton, which are microscopic plants and animals. However, the BBC program Planet Earth filmed a whale shark feeding on a school of small fish. The same documentary showed footage of a whale shark timing its arrival to coincide with the mass spawning of fish shoals and feeding on the resultant clouds of eggs and sperm.
The species was distinguished in April 1828 after the harpooning of a 4.6 metres (15.1 ft) specimen in Table Bay, South Africa. Andrew Smith, a military doctor associated with British troops stationed in Cape Town, described it the following year. The name "whale shark" comes from the fish's physiology, being as large as many whales and also a filter feeder like many whale species.
number 98 on explore on April 13th 2012
Kew Gardens is the world's largest collection of living plants. Founded in 1840 from the exotic garden at Kew Park in the London Borough of Richmond upon Thames, UK, its living collections include more than 30,000 different kinds of plants, while the herbarium, which is one of the largest in the world, has over seven million preserved plant specimens. The library contains more than 750,000 volumes, and the illustrations collection contains more than 175,000 prints and drawings of plants. It is one of London's top tourist attractions. In 2003, the gardens were put on the UNESCO list of World Heritage Sites.
Kew Gardens, together with the botanic gardens at Wakehurst Place in Sussex, are managed by the Royal Botanic Gardens, Kew (brand name Kew), an internationally important botanical research and education institution that employs 750 staff, and is a non-departmental public body sponsored by the Department for Environment, Food and Rural Affairs.
The Kew site, which has been dated as formally starting in 1759, though can be traced back to the exotic garden at Kew Park, formed by Lord Capel John of Tewkesbury, consists of 121 hectares (300 acres) of gardens and botanical glasshouses, four Grade I listed buildings and 36 Grade II listed structures, all set in an internationally significant landscape.
Kew Gardens has its own police force, Kew Constabulary, which has been in operation since 1847.
History
Kew, the area in which Kew Gardens are situated, consists mainly of the gardens themselves and a small surrounding community. Royal residences in the area which would later influence the layout and construction of the gardens began in 1299 when Edward I moved his court to a manor house in neighbouring Richmond (then called Sheen). That manor house was later abandoned; however, Henry V built Sheen Palace in 1501, which, under the name Richmond Palace, became a permanent royal residence for Henry VII. Around the start of the 16th century courtiers attending Richmond Palace settled in Kew and built large houses. Early royal residences at Kew included Mary Tudor's house, which was in existence by 1522 when a driveway was built to connect it to the palace at Richmond. Around 1600, the land that would become the gardens was known as Kew Field, a large field strip farmed by one of the new private estates.
The exotic garden at Kew Park, formed by Lord Capel John of Tewkesbury, was enlarged and extended by Augusta, Dowager Princess of Wales, the widow of Frederick, Prince of Wales. The origins of Kew Gardens can be traced to the merging of the royal estates of Richmond and Kew in 1772. William Chambers built several garden structures, including the lofty Chinese pagoda built in 1761 which still remains. George III enriched the gardens, aided by William Aiton and Sir Joseph Banks. The old Kew Park (by then renamed the White House), was demolished in 1802. The "Dutch House" adjoining was purchased by George III in 1781 as a nursery for the royal children. It is a plain brick structure now known as Kew Palace.
Some early plants came from the walled garden established by William Coys at Stubbers in North Ockendon. The collections grew somewhat haphazardly until the appointment of the first collector, Francis Masson, in 1771. Capability Brown, who became England's most renowned landscape architect, applied for the position of master gardener at Kew, and was rejected.
In 1840 the gardens were adopted as a national botanical garden, in large part due to the efforts of the Royal Horticultural Society and its president William Cavendish. Under Kew's director, William Hooker, the gardens were increased to 30 hectares (75 acres) and the pleasure grounds, or arboretum, extended to 109 hectares (270 acres), and later to its present size of 121 hectares (300 acres). The first curator was John Smith.
The Palm House was built by architect Decimus Burton and iron-maker Richard Turner between 1844 and 1848, and was the first large-scale structural use of wrought iron. It is considered " the world's most important surviving Victorian glass and iron structure." The structure's panes of glass are all hand-blown. The Temperate House, which is twice as large as the Palm House, followed later in the 19th century. It is now the largest Victorian glasshouse in existence. Kew was the location of the successful effort in the 19th century to propagate rubber trees for cultivation outside South America.
In February 1913, the Tea House was burned down by suffragettes Olive Wharry and Lilian Lenton during a series of arson attacks in London.[19] Kew Gardens lost hundreds of trees in the Great Storm of 1987. From 1959 to 2007 Kew Gardens had the tallest flagpole in Britain. Made from a single Douglas-fir from Canada, it was given to mark both the centenary of the Canadian Province of British Columbia and the bicentenary of Kew Gardens. The flagpole was removed after damage by weather and woodpeckers.
In July 2003, the gardens were put on the list of World Heritage Sites by UNESCO.
Features
Treetop walkway
A new treetop walkway opened in 2008. This walkway is 18 metres (59 ft) high and 200 metres (660 ft) long and takes visitors into the tree canopy of a woodland glade. Visitors can ascend and descend by stairs or by a lift. The floor of the walkway is made from perforated metal and flexes as it is walked upon. The entire structure sways in the wind.
Sackler Crossing
The Sackler Crossing bridge, made of granite and bronze, opened in May 2006. Designed by Buro Happold and John Pawson, it crosses the lake and is named in honour of philanthropists Dr Mortimer and Theresa Sackler.
The minimalist-styled bridge is designed as a sweeping double curve of black granite. The sides of the bridge are formed of bronze posts that give the impression, from certain angles, of forming a solid wall whereas from others, and to those on the bridge, they are clearly individual entities that allow a view of the water beyond.
The bridge forms part of a path designed to encourage visitors to visit more of the gardens than had hitherto been popular and connects the two art galleries, via the Temperate and Evolution Houses and the woodland glade, to the Minka House and the Bamboo Garden.
The crossing won a special award from the Royal Institute of British Architects in 2008.
Vehicular tour
Kew Explorer is a service that takes a circular route around the gardens, provided by two 72-seater road trains that are fuelled by Calor Gas to minimise pollution. A commentary is provided by the driver and there are several stops.
Compost heap
Kew has one of the largest compost heaps in Europe, made from green and woody waste from the gardens and the manure from the stables of the Household Cavalry. The compost is mainly used in the gardens, but on occasion has been auctioned as part of a fundraising event for the gardens.
The compost heap is in an area of the gardens not accessible to the public, but a viewing platform, made of wood which had been illegally traded but seized by Customs officers in HMRC, has been erected to allow visitors to observe the heap as it goes through its cycle.
Guided walks
Free tours of the gardens are conducted daily by trained volunteers.
Plant houses
Alpine House
A narrow semicircular building of glass and steel latticework stands at the right, set amid an area of worked rock with a line of deciduous trees in the rear left, under a blue sky filled with large puffy white clouds. In front of it, curving slightly away to the left, is a wooden platform with benches on it and a thin metal guardrail in front of a low wet area with bright red flowers
In March 2006, the Davies Alpine House opened, the third version of an alpine house since 1887. Although only 16 metres (52 ft) long the apex of the roof arch extends to a height of 10 metres (33 ft) in order to allow the natural airflow of a building of this shape to aid in the all-important ventilation required for the type of plants to be housed.
The new house features a set of automatically operated blinds that prevent it overheating when the sun is too hot for the plants together with a system that blows a continuous stream of cool air over the plants. The main design aim of the house is to allow maximum light transmission. To this end the glass is of a special low iron type that allows 90 per cent of the ultraviolet light in sunlight to pass. It is attached by high tension steel cables so that no light is obstructed by traditional glazing bars.
To conserve energy the cooling air is not refrigerated but is cooled by being passed through a labyrinth of pipes buried under the house at a depth where the temperature remains suitable all year round. The house is designed so that the maximum temperature should not exceed 20 °C (68 °F).
Kew's collection of Alpine plants (defined as those that grow above the tree-line in their locale – ground level at the poles rising to over 2,000 metres (6,562 feet)), extends to over 7000. As the Alpine House can only house around 200 at a time the ones on show are regularly rotated.
The Nash Conservatory
Originally designed for Buckingham Palace, this was moved to Kew in 1836 by King William IV. With an abundance of natural light, the building is used various exhibitions, weddings, and private events. It is also now used to exhibit the winners of the photography competition.
Kew Orangery
The Orangery was designed by Sir William Chambers, and was completed in 1761. It measures 28 by 10 metres (92 by 33 ft). It was found to be too dark for its intended purpose of growing citrus plants and they were moved out in 1841. After many changes of use, it is currently used as a restaurant.
The Palm House and Parterre
The Palm House (1844–1848) was the result of cooperation between architect Decimus Burton and iron founder Richard Turner,[28] and continues upon the glass house design principles developed by John Claudius Loudon[29][30] and Joseph Paxton. A space frame of wrought iron arches, held together by horizontal tubular structures containing long prestressed cables,[30][31] supports glass panes which were originally[28] tinted green with copper oxide to reduce the significant heating effect. The 19m high central nave is surrounded by a walkway at 9m height, allowing visitors a closer look upon the palm tree crowns. In front of the Palm House on the east side are the Queen's Beasts, ten statues of animals bearing shields. They are Portland stone replicas of originals done by James Woodford and were placed here in 1958.[32]
Princess of Wales Conservatory
Kew's third major conservatory, the Princess of Wales Conservatory, designed by architect Gordon Wilson, was opened in 1987 by Diana, Princess of Wales in commemoration of her predecessor Augusta's associations with Kew. In 1989 the conservatory received the Europa Nostra award for conservation.[34] The conservatory houses ten computer-controlled micro-climatic zones, with the bulk of the greenhouse volume composed of Dry Tropics and Wet Tropics plants. Significant numbers of orchids, water lilies, cacti, lithops, carnivorous plants and bromeliads are housed in the various zones. The cactus collection also extends outside the conservatory where some hardier species can be found.
The conservatory has an area of 4499 square metres. As it is designed to minimise the amount of energy taken to run it, the cooler zones are grouped around the outside and the more tropical zones are in the central area where heat is conserved. The glass roof extends down to the ground, giving the conservatory a distinctive appearance and helping to maximise the use of the sun's energy.
During the construction of the conservatory a time capsule was buried. It contains the seeds of basic crops and endangered plant species and key publications on conservation.
Rhizotron
The Rhizotron
A rhizotron opened at the same time as the "treetop walkway", giving visitors the opportunity to investigate what happens beneath the ground where trees grow. The rhizotron is essentially a single gallery containing a set of large bronze abstract castings which contain LCD screens that carry repeating loops of information about the life of trees.
Temperate House
Inside the Temperate House
The Temperate House, currently closed for restoration, is a greenhouse that has twice the floor area of the Palm House and is the world's largest surviving Victorian glass structure. When in use it contained plants and trees from all the temperate regions of the world. It was commissioned in 1859 and designed by architect Decimus Burton and ironfounder Richard Turner. Covering 4880 square metres, it rises to a height of 19 metres. Intended to accommodate Kew's expanding collection of hardy and temperate plants, it took 40 years to construct, during which time costs soared. The building was restored during 2014 - 15 by Donald Insall Associates, based on their conservation management plan.
There is a viewing gallery in the central section from which visitors were able to look down on that part of the collection.
Waterlily House
The Waterlily House is the hottest and most humid of the houses at Kew and contains a large pond with varieties of water lily, surrounded by a display of economically important heat-loving plants. It closes during the winter months.
It was built to house the Victoria amazonica, the largest of the Nymphaeaceae family of water lilies. This plant was originally transported to Kew in phials of clean water and arrived in February 1849, after several prior attempts to transport seeds and roots had failed. Although various other members of the Nymphaeaceae family grew well, the house did not suit the Victoria, purportedly because of a poor ventilation system, and this specimen was moved to another, smaller, house.
The ironwork for this project was provided by Richard Turner and the initial construction was completed in 1852. The heat for the house was initially obtained by running a flue from the nearby Palm House but it was later equipped with its own boiler.
Ornamental buildings
The Pagoda
In the south-east corner of Kew Gardens stands the Great Pagoda (by Sir William Chambers), erected in 1762, from a design in imitation of the Chinese Ta. The lowest of the ten octagonal storeys is 15 m (49 ft) in diameter. From the base to the highest point is 50 m (164 ft).
Each storey finishes with a projecting roof, after the Chinese manner, originally covered with ceramic tiles and adorned with large dragons; a story is still propagated that they were made of gold and were reputedly sold by George IV to settle his debts. In fact the dragons were made of wood painted gold, and simply rotted away with the ravages of time. The walls of the building are composed of brick. The staircase, 253 steps, is in the centre of the building. The Pagoda was closed to the public for many years, but was reopened for the summer months of 2006 and is now open permanently. During the Second World War holes were cut in each floor to allow for drop-testing of model bombs.
The Japanese Gateway (Chokushi-Mon)
Built for the Japan-British Exhibition (1910) and moved to Kew in 1911, the Chokushi-Mon ("Imperial Envoy's Gateway") is a four-fifths scale replica of the karamon (gateway) of the Nishi Hongan-ji temple in Kyoto. It lies about 140 m west of the Pagoda and is surrounded by a reconstruction of a traditional Japanese garden.
The Minka House
Following the Japan 2001 festival, Kew acquired a Japanese wooden house called a minka. It was originally erected in around 1900 in a suburb of Okazaki. Japanese craftsmen reassembled the framework and British builders who had worked on the Globe Theatre added the mud wall panels.
Work on the house started on 7 May 2001 and, when the framework was completed on 21 May, a Japanese ceremony was held to mark what was considered an auspicious occasion. Work on the building of the house was completed in November 2001 but the internal artefacts were not all in place until 2006.
The Minka house is located within the bamboo collection in the west central part of the gardens.
Queen Charlotte's Cottage
Within the conservation area is a cottage that was given to Queen Charlotte as a wedding present on her marriage to George III. It has been restored by Historic Royal Palaces and is separately administered by them.
It is open to the public on weekends and bank holidays during the summer.
Kew Palace
Kew Palace is the smallest of the British royal palaces. It was built by Samuel Fortrey, a Dutch merchant in around 1631. It was later purchased by George III. The construction method is known as Flemish bond and involves laying the bricks with long and short sides alternating. This and the gabled front give the construction a Dutch appearance.
To the rear of the building is the "Queen's Garden" which includes a collection of plants believed to have medicinal qualities. Only plants that were extant in England by the 17th century are grown in the garden.
The building underwent significant restoration, with leading conservation architects Donald Insall Associates, before being reopened to the public in 2006.
It is administered separately from Kew Gardens, by Historic Royal Palaces.
In front of the palace is a sundial, which was given to Kew Gardens in 1959 to commemorate a royal visit. It was sculpted by Martin Holden and is based on an earlier sculpture by Thomas Tompion, a celebrated 17th century clockmaker.
Galleries and Museums
The Shirley Sherwood Gallery of Botanic Art
The Shirley Sherwood Gallery of Botanic Art opened in April 2008, and holds paintings from Kew's and Dr Shirley Sherwood's collections, many of which had never been displayed to the public before. It features paintings by artists such as Georg D. Ehret, the Bauer brothers, Pierre-Joseph Redouté and Walter Hood Fitch. The paintings and drawings are cycled on a six-monthly basis. The gallery is linked to the Marianne North Gallery (see above).
Near the Palm House is a building known as "Museum No. 1" (even though it is the only museum on the site), which was designed by Decimus Burton and opened in 1857. Housing Kew's economic botany collections including tools, ornaments, clothing, food and medicines, its aim was to illustrate human dependence on plants. The building was refurbished in 1998. The upper two floors are now an education centre and the ground floor houses the "Plants+People" exhibition which highlights the variety of plants and the ways that people use them.
Admission to the galleries and museum is free after paying admission to the gardens. The International Garden Photographer of the Year Exhibition is an annual event with an indoor display of entries during the summer months.
The Marianne North Gallery of Botanic Art
The Marianne North Gallery was built in the 1880s to house the paintings of Marianne North, an MP's daughter who travelled alone to North and South America, South Africa and many parts of Asia, at a time when women rarely did so, to paint plants. The gallery has 832 of her paintings. The paintings were left to Kew by the artist and a condition of the bequest is that the layout of the paintings in the gallery may not be altered.
The gallery had suffered considerable structural degradation since its creation and during a period from 2008 to 2009 major restoration and refurbishment took place, with works lead by with leading conservation architects Donald Insall Associates. During the time the gallery was closed the opportunity was also taken to restore the paintings to their original condition. The gallery reopened in October 2009.
The gallery originally opened in 1882 and is the only permanent exhibition in Great Britain dedicated to the work of one woman.
Plant collections
The plant collections include the Aquatic Garden, which is near the Jodrell laboratory. The Aquatic Garden, which celebrated its centenary in 2009, provides conditions for aquatic and marginal plants. The large central pool holds a selection of summer-flowering water lilies and the corner pools contain plants such as reed mace, bulrushes, phragmites and smaller floating aquatic species.
The Arboretum, which covers over half of the total area of the site, contains over 14,000 trees of many thousands of varieties. The Bonsai Collection is housed in a dedicated greenhouse near the Jodrell laboratory. The Cacti Collection is housed in and around the Princess of Wales Conservatory. The Carnivorous Plant collection is housed in the Princess of Wales Conservatory. The Grass Garden was created on its current site in the early 1980s to display ornamental and economic grasses; it was redesigned and replanted between 1994 and 1997. It is currently undergoing a further redesign and planting. Over 580 species of grasses are displayed.
The Herbaceous Grounds (Order Beds) were devised in the late 1860s by Sir Joseph Hooker, then director of the Royal Botanic Gardens, so that botany students could learn to recognise plants and experience at first hand the diversity of the plant kingdom. The collection is organised into family groups. Its name arose because plant families were known as natural orders in the 19th century. Over the main path is a rose pergola built in 1959 to mark the bicentennial of the Gardens. It supports climber and rambling roses selected for the length and profusion of flowering.
The Orchid Collection is housed in two climate zones within the Princess of Wales Conservatory. To maintain an interesting display the plants are changed regularly so that those on view are generally flowering. The Rock Garden, originally built of limestone in 1882, is now constructed of Sussex sandstone from West Hoathly, Sussex. The rock garden is divided into six geographic regions: Europe, Mediterranean and Africa, Australia and New Zealand, Asia, North America, and South America. There are currently 2,480 different "accessions" growing in the garden.
The Rose Garden, based upon original designs by William Nesfield, is behind the Palm House, and was replanted between 2009 and 2010 using the original design from 1848. It is intended as an ornamental display rather than a collection of a particularly large number of varieties. Other collections and specialist areas include the rhododendron dell, the azalea garden, the bamboo garden, the juniper collection, the berberis dell, the lilac garden, the magnolia collection, and the fern collection.
The Palm House and lake to Victoria Gate
The world's smallest water-lily, Nymphaea thermarum, was saved from extinction when it was grown from seed at Kew, in 2009.
Herbarium
The Kew herbarium is one of the largest in the world with approximately 7 million specimens used primarily for taxonomic study. The herbarium is rich in types for all regions of the world, especially the tropics.
Library and archives
The library and archives at Kew are one of the world's largest botanical collections, with over half a million items, including books, botanical illustrations, photographs, letters and manuscripts, periodicals, and maps. The Jodrell Library has been merged with the Economic Botany and Mycology Libraries and all are now housed in the Jodrell Laboratory.
Forensic horticulture
Kew provides advice and guidance to police forces around the world where plant material may provide important clues or evidence in cases. In one famous case the forensic science department at Kew were able to ascertain that the contents of the stomach of a headless corpse found in the river Thames contained a highly toxic African bean.
Economic Botany
The Sustainable Uses of Plants group (formerly the Centre for Economic Botany), focus on the uses of plants in the United Kingdom and the world's arid and semi-arid zones. The Centre is also responsible for curation of the Economic Botany Collection, which contains more than 90,000 botanical raw materials and ethnographic artefacts, some of which are on display in the Plants + People exhibit in Museum No. 1. The Centre is now located in the Jodrell Laboratory.
Jodrell Laboratory
The original Jodrell laboratory, named after Mr T. J. Phillips Jodrell who funded it, was established in 1877 and consisted of four research rooms and an office. Originally research was conducted into plant physiology but this was gradually superseded by botanical research. In 1934 an artists' studio and photographic darkroom were added, highlighting the importance of botanical illustration. In 1965, following increasing overcrowding, a new building was constructed and research expanded into seed collection for plant conservation. The biochemistry section also expanded to facilitate research into secondary compounds that could be derived from plants for medicinal purposes. In 1994 the centre was expanded again, tripling in size, and a decade later it was further expanded by the addition of the Wolfson Wing.
Kew Constabulary
Main article: Kew Constabulary
The gardens have their own police force, Kew Constabulary, which has been in operation since 1847. Formerly known as the Royal Botanic Gardens Constabulary, it is a small, specialised constabulary of two sergeants and 12 officers, who patrol the grounds in a green painted electric buggy. The Kew Constables are attested under section 3 of the Parks Regulation Act 1872, which gives them the same powers as the Metropolitan Police within the land belonging to the gardens.
Media
A number of films, documentaries and short videos have been made about Kew Gardens.
They include:
a short colour film World Garden by cinematographer Geoffrey Unsworth in 1942
three series of A Year at Kew (2007), filmed for BBC television and released on DVD
Cruickshank on Kew: The Garden That Changed the World, a 2009 BBC documentary, presented by Dan Cruickshank, exploring the history of the relationship between Kew Gardens and the British Empire
David Attenborough's 2012 Kingdom of Plants 3D
a 2003 episode of the Channel 4 TV series Time Team, presented by Tony Robinson, that searched for the remains of George III's palace
a 2004 episode of the BBC Four series Art of the Garden which looked at the building of the Great Palm House in the 1840s.
"Kew on a Plate", a TV programme showing the kinds of produce grown at Kew Gardens and how they can be prepared in a kitchen.
In 1921 Virginia Woolf published her short story "Kew Gardens", which gives brief descriptions of four groups of people as they pass by a flowerbed.
Access and transport
Elizabeth Gate
Kew Gardens is accessible by a number of gates. Currently, there are four gates into Kew Gardens that are open to the public: the Elizabeth Gate, which is situated at the west end of Kew Green, and was originally called the Main Gate before being renamed in 2012 to commemorate the Diamond Jubilee of Elizabeth II; the Brentford Gate, which faces the River Thames; the Victoria Gate (named after Queen Victoria), situated in Kew Road, which is also the location of the Visitors' Centre; and the Lion Gate, also situated in Kew Road.
Other gates that are not open to the public include Unicorn Gate, Cumberland Gate and Jodrell Gate (all in Kew Road) and Isleworth Gate (facing the Thames).
Victoria Gate
Kew Gardens station, a London Underground and National Rail station opened in 1869 and served by both the District line and the London Overground services on the North London Line, is the nearest train station to the gardens – only 400 metres (1,300 ft) along Lichfield Road from the Victoria Gate entrance. Built by the London and South Western Railway, the Historic England listed building is one of the few remaining original 19th-century stations on the North London Line, and the only station on the London Underground with a pub on the platform (though the platform entrance is now closed off). Kew Bridge station, on the other side of the Thames, 800 metres from the Elizabeth Gate entrance via Kew Bridge, is served by South West Trains from Clapham Junction and Waterloo.
London Buses route 65, between Ealing Broadway and Kingston, stops near the Lion Gate and Victoria Gate entrances; route 391, between Fulham and Richmond, stops near Kew Gardens station; while routes 237 and 267 stop at Kew Bridge station.
London River Services operate from Westminster during the summer, stopping at Kew Pier, 500 metres (1,600 ft) from Elizabeth Gate. Cycle racks are located just inside the Victoria Gate, Elizabeth Gate and Brentford Gate entrances. There is a 300-space car park outside Brentford Gate, reached via Ferry Lane, as well as some free, though restricted, on-street parking on Kew Road.
www.nlm.nih.gov/exhibition/historicalanatomies/cheselden_...
Cheselden, William. Osteographia, or The anatomy of the bones. (London: [William Bowyer for the author?], 1733).
Lithograph of skull, pasted into: Anatomy improv'd and illustrated with regard to the uses thereof in designing. (London: John Senex, 1723).
This volume of engraved plates and text was originally published in Rome in 1691, and was re-engraved and republished in London in 1723. The dissections were done for the Italian edition by Bernardino Genga, Professor of Anatomy and Surgery and physician in the hospital of San Spirito in Rome, and the explanatory text by the papal physician Giovanni Maria Lancisi (1654-1720). The book, designed for artists rather than medical students, includes plates of famous classical statues from Rome and is described as 'A work of great use to painters, sculptors, statuaries and all others studious in the noble arts of design'.
The English edition is dedicated by the publisher to Richard Mead, FRCP, FRS (1673-1754), 'a favourer of the politer arts'.
Part of the Anatomical Atlases in Special Collections & Archives, SPEC Anatomy 6. Cropped inscription on the titlepage, 'Tho. Dixon's Book 1799' and the pencilled name' Miss Annie Jackson, 19 North Street' on the front flyleaf, with pencil measurements possibly from a dissected skeleton on the back of the last (index) page.
The volume has had some plates cut out, but has also been grangerised with later anatomical illustrations pasted in.
Medical Education
Image of bones/skeleton
Engraved plate showing human skeleton, probably from a French edition of Andreas Vesalius De corporis humani fabrica libri septem, pasted into: Anatomy improv'd and illustrated with regard to the uses thereof in designing. (London: John Senex, 1723).
This volume of engraved plates and text was originally published in Rome in 1691, and was re-engraved and republished in London in 1723. The dissections were done for the Italian edition by Bernardino Genga, Professor of Anatomy and Surgery and physician in the hospital of San Spirito in Rome, and the explanatory text by the papal physician Giovanni Maria Lancisi (1654-1720). The book, designed for artists rather than medical students, includes plates of famous classical statues from Rome and is described as 'A work of great use to painters, sculptors, statuaries and all others studious in the noble arts of design'.
The English edition is dedicated by the publisher to Richard Mead, FRCP, FRS (1673-1754), 'a favourer of the politer arts'.
Part of the Anatomical Atlases in Special Collections & Archives, SPEC Anatomy 6. Cropped inscription on the titlepage, 'Tho. Dixon's Book 1799' and the pencilled name' Miss Annie Jackson, 19 North Street' on the front flyleaf, with pencil measurements possibly from a dissected skeleton on the back of the last (index) page.
The volume has had some plates cut out, but has also been grangerised with later anatomical illustrations pasted in.
Medical Education
Image of bones/skeleton
Engraving of rear view of the bones of the torso, spine and pelvis by Andrew Bell, pasted into: Anatomy improv'd and illustrated with regard to the uses thereof in designing. (London: John Senex, 1723).
This volume of engraved plates and text was originally published in Rome in 1691, and was re-engraved and republished in London in 1723. The dissections were done for the Italian edition by Bernardino Genga, Professor of Anatomy and Surgery and physician in the hospital of San Spirito in Rome, and the explanatory text by the papal physician Giovanni Maria Lancisi (1654-1720). The book, designed for artists rather than medical students, includes plates of famous classical statues from Rome and is described as 'A work of great use to painters, sculptors, statuaries and all others studious in the noble arts of design'.
The English edition is dedicated by the publisher to Richard Mead, FRCP, FRS (1673-1754), 'a favourer of the politer arts'.
Part of the Anatomical Atlases in Special Collections & Archives, SPEC Anatomy 6. Cropped inscription on the titlepage, 'Tho. Dixon's Book 1799' and the pencilled name' Miss Annie Jackson, 19 North Street' on the front flyleaf, with pencil measurements possibly from a dissected skeleton on the back of the last (index) page.
The volume has had some plates cut out, but has also been grangerised with later anatomical illustrations pasted in.Medical Education
Image of bones/skeleton
torso
Plate 2 showing engraving of front view of 'the Bones of the Trunk or Human Busto' from: Anatomy improv'd and illustrated with regard to the uses thereof in designing. (London: John Senex, 1723).
This volume of engraved plates and text was originally published in Rome in 1691, and was re-engraved and republished in London in 1723. The dissections were done for the Italian edition by Bernardino Genga, Professor of Anatomy and Surgery and physician in the hospital of San Spirito in Rome, and the explanatory text by the papal physician Giovanni Maria Lancisi (1654-1720). The book, designed for artists rather than medical students, includes plates of famous classical statues from Rome and is described as 'A work of great use to painters, sculptors, statuaries and all others studious in the noble arts of design'.
The English edition is dedicated by the publisher to Richard Mead, FRCP, FRS (1673-1754), 'a favourer of the politer arts'.
Part of the Anatomical Atlases in Special Collections & Archives, SPEC Anatomy 6. Cropped inscription on the titlepage, 'Tho. Dixon's Book 1799' and the pencilled name' Miss Annie Jackson, 19 North Street' on the front flyleaf, with pencil measurements possibly from a dissected skeleton on the back of the last (index) page.
The volume has had some plates cut out, but has also been grangerised with later anatomical illustrations pasted in.
Medical Education
Image of bones/skeleton torso
Plate 2 showing engraving of rear view of 'the Bones of the Trunk or Human Busto' from: Anatomy improv'd and illustrated with regard to the uses thereof in designing. (London: John Senex, 1723).
This volume of engraved plates and text was originally published in Rome in 1691, and was re-engraved and republished in London in 1723. The dissections were done for the Italian edition by Bernardino Genga, Professor of Anatomy and Surgery and physician in the hospital of San Spirito in Rome, and the explanatory text by the papal physician Giovanni Maria Lancisi (1654-1720). The book, designed for artists rather than medical students, includes plates of famous classical statues from Rome and is described as 'A work of great use to painters, sculptors, statuaries and all others studious in the noble arts of design'.
The English edition is dedicated by the publisher to Richard Mead, FRCP, FRS (1673-1754), 'a favourer of the politer arts'.
Part of the Anatomical Atlases in Special Collections & Archives, SPEC Anatomy 6. Cropped inscription on the titlepage, 'Tho. Dixon's Book 1799' and the pencilled name' Miss Annie Jackson, 19 North Street' on the front flyleaf, with pencil measurements possibly from a dissected skeleton on the back of the last (index) page.
The volume has had some plates cut out, but has also been grangerised with later anatomical illustrations pasted in.Medical Education
Image of bones/skeleton
torso
Photos taken from an outing with the Deep Water Sharks and Shark Stress Psysiology research groups. The two reserach groups teamed up to deploy a longline over 600 meters deep of the Exuma Sound. The groups were able to catch a Bigeyed Sixgill Skark (Hexanchus nakamurai). Once caught the Sixgill was tagged and blood samples were taking. The line took over an hour and a half to haul up and the entire process of tagging, taking blood samples, and then releasing the Sixgill took under 10 minutes.
Plate 2 showing engraving of front view of 'the Bones of the Trunk or Human Busto' from: Anatomy improv'd and illustrated with regard to the uses thereof in designing. (London: John Senex, 1723).
This volume of engraved plates and text was originally published in Rome in 1691, and was re-engraved and republished in London in 1723. The dissections were done for the Italian edition by Bernardino Genga, Professor of Anatomy and Surgery and physician in the hospital of San Spirito in Rome, and the explanatory text by the papal physician Giovanni Maria Lancisi (1654-1720). The book, designed for artists rather than medical students, includes plates of famous classical statues from Rome and is described as 'A work of great use to painters, sculptors, statuaries and all others studious in the noble arts of design'.
The English edition is dedicated by the publisher to Richard Mead, FRCP, FRS (1673-1754), 'a favourer of the politer arts'.
Part of the Anatomical Atlases in Special Collections & Archives, SPEC Anatomy 6. Cropped inscription on the titlepage, 'Tho. Dixon's Book 1799' and the pencilled name' Miss Annie Jackson, 19 North Street' on the front flyleaf, with pencil measurements possibly from a dissected skeleton on the back of the last (index) page.
The volume has had some plates cut out, but has also been grangerised with later anatomical illustrations pasted in.Medical Education
Image of bones/skeleton
torso
Plate 2, figure 1 from Jones QUAIN's The viscera of the human body (1840) showing the anatomy of the mouth.
Known as Quain's Plates, this book was the fourth in a series of five volumes of anatomical plates (1836-1842), with references and physiological comments, edited by Jones Quain and William James Erasmus Wilson.
They aimed to provide students with affordable access to high quality illustrations with English commentary. Their comments give detailed descriptions of the parts of the body in the illustration, and explain the process of dissection needed to show them.
The original drawings by W.Bagg were done from nature then lithographed by William Fairland for reproduction.
Part of the Anatomical Atlases in Special Collections & Archives, SPEC Anatomy 12.
One copy of these plates was part of the Medical Library of the Liverpool Infirmary before passing to the Departmental Library in Anatomy.
Images from Special Collections & Archives, the University of Liverpool.
Engraved titlepage vignette by J. Sturt showing skeletons from Anatomy improv'd and illustrated with regard to the uses thereof in designing. (London: John Senex, 1723).
This volume of engraved plates and text was originally published in Rome in 1691, and was re-engraved and republished in London in 1723. The dissections were done for the Italian edition by Bernardino Genga, Professor of Anatomy and Surgery and physician in the hospital of San Spirito in Rome, and the explanatory text by the papal physician Giovanni Maria Lancisi (1654-1720). The book, designed for artists rather than medical students, includes plates of famous classical statues from Rome and is described as 'A work of great use to painters, sculptors, statuaries and all others studious in the noble arts of design'.
The English edition is dedicated by the publisher to Richard Mead, FRCP, FRS (1673-1754), 'a favourer of the politer arts'.
Part of the Anatomical Atlases in Special Collections & Archives, SPEC Anatomy 6. Cropped inscription on the titlepage, 'Tho. Dixon's Book 1799' and the pencilled name' Miss Annie Jackson, 19 North Street' on the front flyleaf, with pencil measurements possibly from a dissected skeleton on the back of the last (index) page.
The volume has had some plates cut out, but has also been grangerised with later anatomical illustrations pasted in.
Images from Medical Archive collections at University of Liverpool
Plate 6 (top) from Jones QUAIN's The vessels of the human body (1837) showing the arteries of the face (fig. 1 top).
Known as Quain's Plates, this book was the second in a series of five volumes of anatomical plates (1836-1842), with references and physiological comments, edited by Jones Quain and William James Erasmus Wilson.
They aimed to provide students with affordable access to high quality illustrations with English commentary. Their comments give detailed descriptions of the parts of the body in the illustration, and explain the process of dissection needed to show them.
The original drawings by J. Walsh were then lithographed by W. Fairland for reproduction.
Part of the Anatomical Atlases collection in Special Collections & Archives, SPEC Anatomy 11. One copy of these plates was part of the Medical Library of the Liverpool Infirmary before passing to the Departmental Library in Anatomy.Images from Medical Archive collections at University of Liverpool.
Photos in the field with the Shark Stress Physiology research team. The research team uses a technique involving longlines with eight separate baited gangions. Each gangion is set up with a trigger, that once tripped, will start recording video via GoPro and record time-on-line and tension. Once a specimine is caught, the team spends approximately 10 minutes or less taking blood samples, tagging, and noting visual characteristics of each shark. On this particular outing off the Atlantic side of Cape Eleuthera the research group set their line parallel with the wall of the Exuma Sound. The caught and tagged two reef sharks - one juvinile and one adolescent.
Colour lithograph of the male and female pelvis (platw 12) from Johnston's students' atlas of the bones and ligaments by Charles W. Cathcart and Francis M. Caird (Edinburgh: Johnston, 1885).
Part of the anatomical atlases collection in Special Collections & Archives, SPEC Anatomy 5. With signature on the titlepage, Herbert Brown, 19 Grove Rd, Wallasey.
Pelvis
A Green-crowned Brilliant hummingbird hangs momentarily from a chain that binds a feeder. These chains are needed for their strength and help prevent animals like the kinkajou from carrying off bird feeders in Costa Rica. But strength is a relative thing, for what animals can match the strength of these tiny, featherweight nectar consuming birds? Their unique cardiovascular system allows their heart to beat at rates in excess of a thousand times a minute, when in flight. In comparison, the human heart beats at rates of 100 – 150 when under the stress of exercise. Unusually large pectoralis muscles can make up in excess of 25% of a hummingbird’s body weight. These muscles help them propel themselves through the air with wingbeats that can top 200 times per minute (depending upon the species). Hummingbirds are not simply unique amongst animals but are unique amongst birds, with flight physiology that can be more closely associated with certain insects than it is with our feather friends. #GreenCrownedBrilliant
Plate 6 (bottom) from Jones QUAIN's The vessels of the human body (1837) showing the internal maxillary artery of the face and the dura mater (fig. 2).
Known as Quain's Plates, this book was the second in a series of five volumes of anatomical plates (1836-1842), with references and physiological comments, edited by Jones Quain and William James Erasmus Wilson.
They aimed to provide students with affordable access to high quality illustrations with English commentary. Their comments give detailed descriptions of the parts of the body in the illustration, and explain the process of dissection needed to show them.
The original drawings by J. Walsh were then lithographed by W. Fairland for reproduction.
Part of the Anatomical Atlases in Special Collections & Archives, SPEC Anatomy 11. One copy of these plates was part of the Medical Library of the Liverpool Infirmary before passing to the Departmental Library in Anatomy.
Detail from plate 9 - engraved anatomical illustration of the bones of the foot from: Anatomy improv'd and illustrated with regard to the uses thereof in designing. (London: John Senex, 1723).
This volume of engraved plates and text was originally published in Rome in 1691, and was re-engraved and republished in London in 1723. The dissections were done for the Italian edition by Bernardino Genga, Professor of Anatomy and Surgery and physician in the hospital of San Spirito in Rome, and the explanatory text by the papal physician Giovanni Maria Lancisi (1654-1720). The book, designed for artists rather than medical students, includes plates of famous classical statues from Rome and is described as 'A work of great use to painters, sculptors, statuaries and all others studious in the noble arts of design'.
The English edition is dedicated by the publisher to Richard Mead, FRCP, FRS (1673-1754), 'a favourer of the politer arts'.
Part of the Anatomical Atlases in Special Collections & Archives, SPEC Anatomy 6. Cropped inscription on the titlepage, 'Tho. Dixon's Book 1799' and the pencilled name' Miss Annie Jackson, 19 North Street' on the front flyleaf, with pencil measurements possibly from a dissected skeleton on the back of the last (index) page.
The volume has had some plates cut out, but has also been grangerised with later anatomical illustrations pasted in.
Medical Education
Image of bones/skeleton of foot
"A fore-view of the womb, fully opened, to shew the child [at 8 months] in its natural situation". Plate 20 from William Hunter, Anatomia uteri humani gravidi tabulis illustrata = The anatomy of the human gravid uterus exhibited in figures (Birmingham: John Baskerville, 1774).
The Anatomy of the human gravid uterus is William Hunter's most famous work,and one of the last works printed by the pioneering Birmingham printer and typefounder, John Baskerville.
The large folio plates reproduce the drawings of Jan van Rymsdyk (fl. 1750-1788), based on dissections in which William Hunter acknowledges his brother John's help. His preface also commentson the favourable weather for dissection he enjoyed in preparing the drawings of his first subject. (Hunter's lectures on anatomy took place during the winter).
The Scottish anatomist, surgeon and male midwife William Hunter (1718-1783) studied at the University of Glasgow and worked with William Cullen at Hamilton before moving to London in 1741. He was a pupil in surgery at St. George's Hospital and was appointed physician extraordinary to Queen Charlotte in 1762, having assisted at the safe delivery of her son. His knowledge of female anatomy in pregnancy also made him an expert witness in cases of infanticide. He founded the Hunterian Museum (now at the University of Glasgow) holding his anatomical and pathological specimen collection and library.
SPEC Anatomy 26, from the Anatomcal Atlases collection in Special Collections and Archves, University of Liverpool Library.
Images from Medical Archive collections at University of Liverpool
Engraving showing side view of the bones of the torso by Andrew Bell, pasted into: Anatomy improv'd and illustrated with regard to the uses thereof in designing. (London: John Senex, 1723).
This volume of engraved plates and text was originally published in Rome in 1691, and was re-engraved and republished in London in 1723. The dissections were done for the Italian edition by Bernardino Genga, Professor of Anatomy and Surgery and physician in the hospital of San Spirito in Rome, and the explanatory text by the papal physician Giovanni Maria Lancisi (1654-1720). The book, designed for artists rather than medical students, includes plates of famous classical statues from Rome and is described as 'A work of great use to painters, sculptors, statuaries and all others studious in the noble arts of design'.
The English edition is dedicated by the publisher to Richard Mead, FRCP, FRS (1673-1754), 'a favourer of the politer arts'.
Part of the Anatomical Atlases in Special Collections & Archives, SPEC Anatomy 6. Cropped inscription on the titlepage, 'Tho. Dixon's Book 1799' and the pencilled name' Miss Annie Jackson, 19 North Street' on the front flyleaf, with pencil measurements possibly from a dissected skeleton on the back of the last (index) page.
The volume has had some plates cut out, but has also been grangerised with later anatomical illustrations pasted in.Medical Education
Image of bones/skeleton
torso
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.
Plate 4 showing engraving of side view of 'the Bones of the Human Body or Trunk' from: Anatomy improv'd and illustrated with regard to the uses thereof in designing. (London: John Senex, 1723).
This volume of engraved plates and text was originally published in Rome in 1691, and was re-engraved and republished in London in 1723. The dissections were done for the Italian edition by Bernardino Genga, Professor of Anatomy and Surgery and physician in the hospital of San Spirito in Rome, and the explanatory text by the papal physician Giovanni Maria Lancisi (1654-1720). The book, designed for artists rather than medical students, includes plates of famous classical statues from Rome and is described as 'A work of great use to painters, sculptors, statuaries and all others studious in the noble arts of design'.
The English edition is dedicated by the publisher to Richard Mead, FRCP, FRS (1673-1754), 'a favourer of the politer arts'.
Part of the Anatomical Atlases in Special Collections & Archives, SPEC Anatomy 6. Cropped inscription on the titlepage, 'Tho. Dixon's Book 1799' and the pencilled name' Miss Annie Jackson, 19 North Street' on the front flyleaf, with pencil measurements possibly from a dissected skeleton on the back of the last (index) page.
The volume has had some plates cut out, but has also been grangerised with later anatomical illustrations pasted in.Medical Education
Image of bones/skeleton torso
Plate 3 (muscles) from Bernhard Siegfried Albinus, Tables of the skeleton and muscles of the human body. (London : printed by H. Woodfall for John and Paul Knapton, 1749).
Large folio plate engraved by Charles Grignion (1717-1810).
The German anatomist Bernhard Siegfried Albinus (1697-1770) studied in Leiden and Paris, and taught surgery and anatomy in Leiden. He made studies of the bones and muscles in particular, and made pioneering attempts to improve the accuracy of anatomical illustration. He also edited the works of Andreas Vesalius.
His large-scale Tabulae sceleti et musculorum corporis humani (Leiden, 1747) was published largely at his own expense; the artist and engraver Jan Wandelaar (1690-1759) added the background scenes.The London 1749 edition gives an English translation of the original Latin text.
SPEC Anatomy 27(3) from the Anatomical atlases collection, Special Collections and Archives, the University of Liverpool Library (plates only).
Images from Medical Archive collections at University of Liverpool
Plate 9 from Henri Scoutetten, La methode ovalaire; ou, nouvelle methode pour amputer dans les articulations (1827). Lithographs showing how to amputate the big toe.
Henri Scoutetten (1799-1871) was a French military surgeon, historian and phrenologist., who also wrote about clubfoot, the Berlin cholera epidemic of 1831, hydrotherapy and chloral.
SPEC P8.27/oversize in Special Collections and Archives, the University of Liverpool Library.
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