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Today I said goodbye to someone who for the last 8 years filled my heart with more warmth and love than I thought would ever be possible. Today I said goodbye to the greatest animal who ever lived - Jerry.
About 19 months ago we found out that Jerry was sick. At the time I was 1/3 of the way through my 365 journey and didn't want to bring attention to the news here on Flickr since I had just lost Abby a mere 2 months prior. We learned Jerry had hyperthyroidism, which explained his noticeable weight loss. Beginning in mid-April of last year, I started administering thyroid medication and steroids to Jerry once daily. His vet informed me that the steroids were temporary but that he'd need the thyroid medication everyday for the rest of his life.
After 6 months, the vet gave me permission to wean Jerry off the steroids. He visited the vet every 2-3 months for check-ups and had comprehensive exams every 6 months. His thyroid levels seemed to be improving to almost what is considered regular.
I was warned about kidney failure being a result of thyroid issues, so we switched his food to a low-protein diet so his kidneys wouldn't have to work as hard to break down his food. Jerry's weight gain was back and forth but his activity level remained the same. During the spring we learned that his blood cell count was very low and could be early signs of feline leukemia or another form of cancer. The vet instructed me to continue with Jerry's thyroid medication and diet and to come in for a follow up on his blood work in a few months.
Our last visit to the vet was in August. Jerry was due for a comprehensive exam and dental cleaning. His blood cell count was even lower and he was showing signs of dehydration. The vet forwent Jerry's vaccinations and dental cleaning and instead gave him fluids and antibiotics via an IV catheter. Upon physical examination, the vet found Jerry's kidneys to be small and hard. His weight was down again and I informed the vet of Jerry's recent diarrhea and vomiting.
At that point, x-rays and ultrasounds would diagnose the cancer that was evidently taking control of Jerry's immune system, but the vet and I decided the best thing we could do for Jerry would be to make sure he was comfortable and bring him back in when I felt he was in too much pain to continue. He was given a 2-week prescription of antibiotics and another round of steroids.
Jerry showed signs of feeling better on the steroids until the beginning of October when he began throwing up daily, sometimes multiple times throughout the day or within an hour. I discontinued the steroids right before our wedding and my dad was kind enough to house sit for us while we were on our honeymoon and took care of Jerry and Riley for a week. He seemed about the same and still his loving, cuddly self upon our return and my dad had no unusual behavior to report. Jerry was still vomiting a few times a week, but that had been a constant since the beginning of summer.
This week we noticed some obvious changes in Jerry. He looked like he had lost more weight; even though he was still eating, his appetite had taken even more of a decline and his body felt frail and bony. His joints would click as he slowly walked up and down the stairs and he appeared to be having more trouble keeping his balance. It was last night that I caught him going potty on the floor, which he had never done in his entire life. He then threw up multiple times within an hour and had remnants dripping out of his mouth with drool. The feelings of what I had experienced with Abby came flooding back and I new it was finally time. We left a message for the vet and brought him to bed.
This morning I woke to find that he had pooped on the floor in our bedroom and had not cleaned himself off. It was all over his bottom and on the bed where he had been sitting. I called the vet as soon as they opened and they were able to squeeze us in. As horrible as it feels to even say the word 'euthanasia,' I knew we had reached that point. From the moment we learned Jerry was sick I did everything I could to stay of top of his medications and vet appointments and gave him as much love as humanely possible. I held him, crying, telling him I loved him while Eric held me. We said goodbye, and the minute it was over a wave rushed over me and I immediately felt better knowing his pain was finally gone. Jerry in no way deserved to live the last year and a half of his life in the condition that he had, but he also no longer deserved to suffer. I felt at peace, but still extremely sad that I had to let go of someone I loved so incredibly much for so long.
Jerry will join Abby in Eric's dad's backyard. He missed her so much when she left us, so I think he will be happy to be resting peacefully beside her. As Riley and I wait for Eric to get home, the house already feels a little emptier. I sit alone at my computer and already miss the purring prince who loved to sit with me here. I hate that he was taken from me, but I have to believe that I gave him everything that I could. I loved him with all of my heart, and he will forever remain there.
RIP Jerry Berry
November 5, 2010
This is an unusual variant of follicular neoplasm of the thyroid gland. It has been described in follicular adenomas, however, this lesion did show destructive capsular invasion. H&E, right; Alcian Blue, left.
cross section: human parathythyroid gland
magnification: 200x phase contrast
hematoxylin eosin stain
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Does it seem like no matter how hard you try you can’t lose weight? Maybe you start to think your thyroid is to blame for your inability to lose weight.
I feel as though I am always being choked by some unseen force (my thyroid nodule) 24/7. The presure is so great that it makes my ear ache.
Minocycline is a tetracycline derivative antibiotic commonly prescribed for acne, rosacea, and other inflammatory skin disorders. Minocycline turns black when oxidized, leading to discoloration of the skin and nails. Pigmentation may also involve the bulbar conjunctiva, oral mucosa, teeth, bones, and thyroid gland. Pigmentation has been reported after long-term minocycline therapy with at least 100 mg/day.
Image contributed by Dr Zubair Baloch - @aakasharmand
Because you know your animals best you will be the first to notice abnormal behavior and therefore we have compiled a list of symptoms which should not be ignored and when they appear should contact the emergency vet soon!
1. Multiple urination and urination problems - These symptoms can often indicate a wide range of diseases, including behavioral problems, kidney failure, diabetes, thyroid problems, urinary tract infections, and more. If you think your dog is drinking or urinating excessively, bring it to the emergency vet for inspection
Signs such as repeated attempts to urinate, urinary incontinence, and blood urination can result from a wide variety of factors. From urinary tract infection to urinary incontinence without treatment can eventually lead to death. Therefore, if such signs appear, it is recommended to contact an emergency vet.
2. Loss of appetite or cessation of eating - Loss of appetite in our dog can be due to many different reasons and in the way it is among the first signs that appear in the condition of illness.
Loss of appetite and lack of eating per se (if they last longer than 24 hours) may affect and affect the health of the dog regardless of the cause of the initial cause. In such a situation it is recommended to diagnose the cause and treat it quickly in order to shorten the time when the dog is not eating while providing the dog with supportive care.
3. Apathy, exhaustion or weakness - manifested in indifference, poor reaction to normal stimuli (name calling, noises, smells, contact). If apathy persists over a period of time, this should not be ignored even if there is no other sign.
4. Diarrhea / vomiting - In this case too, these symptoms can be caused by a wide variety of medical conditions or conditions related to the digestive system or other digestive system.
If this is a diuretic or black diarrhea, this may indicate bleeding to the digestive system in its various parts. Vomiting can also suggest gastrointestinal bleeding, especially the upper gastrointestinal tract. In case of vomiting or diarrhea, contact your emergency vet.
5. Non-productive vomiting - Frequent and unsuccessful attempts to vomit may indicate gastric inversion (GDV). This situation is a life threatening situation that requires immediate contact with an emergency vet.
6. Fainting or fainting - a situation in which the dog is unable to stand on its own feet, in some cases the dog quickly regains its temper and in others it takes him some time to recover. Any case of breakdown or weakness is a good reason to contact an immediate emergency vet.
7. Twitching - Twitch is a general name for a varied appearance of nerve signs. In the language of the people, it is called epilepsy (although epilepsy is also a type of spasm, but not every spasm is epilepsy).
The spasm can be mild and can be expressed, for example, in facial movements ("bags") and can be more difficult to manifest in the collapse of the dog, including involuntary movements of the legs, incontinence (feces and urine). The spasm can last from seconds to long minutes, in these cases it usually takes time for the dog to recover and regain itself.
Spasms usually result from over-stimulation of the nervous system when the cause can be systemic or focused on the nervous system. There are life-threatening convulsions. In any case, contact an emergency vet.
cross section: human parathythyroid gland
magnification: 100x
hematoxylin eosin stain
Technical Questions:bioimagesoer@gmail.com
cross section: human thyroid gland
magnification: 100x phase contrast
hematoxylin eosin stain
Technical Questions:bioimagesoer@gmail.com
Thyroid gland > Congenital anomalies > Solid cell nests.
Clear cells.
Image courtesy of Andrey Bychkov, M.D., Ph.D. See topic here.
cross section: human parathythyroid gland
magnification: 200x phase contrast
hematoxylin eosin stain
Technical Questions:bioimagesoer@gmail.com
And I survived it. I walked up the hill. And I walked back down the curvy hill. And that's an accomplishment.
For me anyway.
Before the fibro, I walked four miles a day, I did yoga and an ab-workout thing. I could walk circles around my kids and the spouse. Then, in 2005, I started to feel sluggish. I thought it was my thyroid acting up. (I have a thyroid condition). Tests showed it wasn't. I slowed from four miles to three a day. Then two. Then one. Then when I got to where I couldn't crank out even a half mile, I stopped walking for exercise. In the middle of all that, I stopped doing the yoga and the ab-workout.
Of course, the weight came on. I gained sixty pounds that first year. They tested me for everything. In that first year, the pain started. Joint pain, body aching pain. And so tired. So very tired.
A doctor increased my thyroid medicine and I started to feel better. I started to walk again- a short distance, a mile. March 3, 2006, I slipped on the ice on my back deck and tore up my knee (again). That set off a two and a half year saga to get a consultation letter from the doctor to see a non-VA surgeon. I went from crutches to a cane following that injury. Then I walked with two canes.
That was the VA's solution for me when both knees were bad. Give me two canes. I named them George and Gracie (the cane I had already, his name is Hank and he's made of wood, George and Gracie were "old-people canes", metal with the ergonomic handle).
For almost two years, I walked with two canes when I had to go further than the distance inside my own house. I looked like a fat, weird robot.
On March 18, 2009, three years after I hurt my knee, I got a knee replacement. I named the metal joint "Steve Austin" and the scar is named "Fronkensteen". That surgery kicked off a fibro flare-up that was too obvious to deny. But it took another year and three months to get a proper diagnosis. I was officially diagnosed with fibromyalgia on June 28, 2010. And now I take medicine to cope.
In that time, more weight came on. I look awful now. I photograph myself very carefully. I rarely take photos of the rest of my body, at least, not as a whole
I've been taking Vicodin for years now- for the pain. In July 2010, I started taking Cyclobenzaprine (a muscle relaxer) and it helped a lot. But after six months, the rheumatologist didn't think it was helping enough. Now I take Gabapentin. One week at one pill a day, then move up to two. After a week of two pills a day, I tried three (a week ago, in fact) and I felt like a drooling zombie. So I went back to two pills a day. .
This day, this walk... I took a pill in the midday again to see if it would zombie me out again. I did not. I feel a bit of a buzz, but not completely looped out of my head.
And... I walked today. On a walk. Uphill. And the only thing that really caused me pain was my feet. (on top of it all, I have foot problems too).
Its a start. Let's see if I can keep it up.
cross section: human thyroid gland
magnification: 100x
hematoxylin eosin stain
Technical Questions:bioimagesoer@gmail.com
A 23 yo female presented with palpitation.
Palpitation for 3 days and fever (reaching 39C at home). Weight loss of 24kg (90 to 66) and fatigue in the past three months.
ROS: hair loss, heat intolerance, tremor, inability to close her eyes properly, irritability and anxiety.
PMH and medications: ??
PSH: had urgent C-section 5 months ago at 6 months (neonatal death).
Allergies: none.
Family history: her sister got hypothyroidism, and her mother has diabetes.
Social history: she is a housewife, married since 6 years with 2 children.
Vital Signs:
T: 37 C
HR: 140, strong and regular.
RR: 18
BP: 154/75
O2 saturation: 97% in room air.
She was able to speak full sentences, not sweating or gasping for air. Cooperative and alert to place, time and person.
Lungs are clear to auscultation.
Pulse is present and strong, regular.
Cardiovascular exam: Clear.
Thyroid exam:
Skin: warm, moist and smooth.
Hands: sweaty, no clubbing, no onycholysis, there is a tremor.
Eyes: widening of the palpebral fissures, positive lid lag.
Neck: swelling in the midline (Goiter), moving with swallowing water, bruit present.
Lower leg: no pretibial myxoedema, intact ankle reflexes.
Thyroid gland > Congenital anomalies > Solid cell nests.
Solid cell nests.
Image courtesy of Andrey Bychkov, M.D., Ph.D. See topic here.
cross section: human thyroid gland
magnification: 100x
hematoxylin eosin stain
Technical Questions:bioimagesoer@gmail.com
Patient underwent subtotal thyroidectomy due to neck disfigurement.
Diagnosis: follicular thyroid carcinoma and multinodular goiter
Contributed by: Dr. Wafaey Fahmy Badawy Mohamed, Sharurah Armed Forces Hospital (Saudi Arabia)
Pregnant and Suffering from Hypothyroidism
Thyroid Problem in a pregnant lady can also affect the developing baby. In the first three months of pregnancy, the baby inside the mother gets the thyroid hormone from the mother. If the mother is suffering from hypothyroidism then the baby will not get enough thyroid hormone. And this can result in various problems with mental development.
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cross section: human parathythyroid gland
magnification: 100x
hematoxylin eosin stain
Technical Questions:bioimagesoer@gmail.com
cross section: human parathythyroid gland
magnification: 100x
hematoxylin eosin stain
Technical Questions:bioimagesoer@gmail.com
Well-defined papillary structures with sharp "anatomic" edges (as opposed to the edges of the flat sheets seen in benign follicular lesions, which appear irregular from having been torn away from a macrofollicle).
Since forgetting crucial stuff like keys for housesitting, and a slew of other miscellaneous detail necessary for running a life, I read this to find out more about the phenomena of declining memory and found it reassuring that I wasn't making it worse with toxic living (drinking, drugs, prescriptions drugs, pollutants), mild past brain injuries not registered as damaging, chronic health problems like diabetes, obesity, high blood pressure, thyroid conditions and chronic fatigue among many others and lastly, or maybe firstly, a ramped up over achiever lifestyle with extreme demands on a functioning frontal lobe.
Declining supplies of estrogen affects memory so there's a reason to rethink hormone therapy. And hearing loss, too, I was interested to read. Apparently so much attention is spent on trying to make out what is heard that the brain picks up less textual information. I always thought the opposite was true of my hearing loss.
The book notes that chronic stress compromises memory and its true, stress does make for my most contentious mess-ups leading to lectures from Catherine who has devised a number of memory aids for herself including asking me to help her remember stuff which I rarely do remember to remember for her, but just asking me seems to help. I rarely ask for help having been an only child raised by only children who also didn't ask for help much. The presence of people is often the cause of complete discombobulation for me (unless they're paying me to help them to focus). Asking for help would improve my relationship in other ways too.
Information overload seems to be the major cause of forgetfulness and multi-tasking. This frontal lobe overload factor also parallels the lives of people in mid life who carry a myriad of responsibilities and haven't yet settled down into a routine schedule of retirement.
The biological cause of memory loss in midlife is the decaying of the myelin sheath covering the tentacle of the neuron that sends messages to other neurons. As this deteriorates we experience blocks in memory and our brain takes a detour. At the same time the frontal lobe which is responsible for screening extraneous data also gets tired resulting in too many distracting thoughts, thus adult onset ADD as the joke goes.
The author writes this exploration of memory as she herself experiences it and what she tries to do about it. There are tedious mental exercises and more fun ones like crossword puzzles. There's a battery of vitamins and supplements, fatty acids, omega 3 and glucose—about $125 a months worth—that comes with the 14-Day Memory Prescription Program Diet. You can also do meditation and neurofeedback all of which she tries out. The final chapter covers the activities of the cognitively well endowed which includes learning a new language, memorizing poetry, moving to another country, playing chess and learning to ballroom dance. This latter appealed to Catherine, but she wants to lead and we discovered that my arms are too long and ungainly for this. I think we'll try chess.
I was assured by the book that one does not loose intellect and if you already have a spry brain you can dodge a lot of the impact of Alzheimer's even, which I knew from reading about the nun's study. What I did gain from reading this book was that it's worth paying attention to information as it's coming in and devising ways to remember it. Later when people get older they get used to this memory weakness and don't worry about it so much.
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.
cross section: human thyroid gland
magnification: 100x phase contrast
hematoxylin eosin stain
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This was an incidental 0.5cm nodule in a thyroid removed for multinodular goiter. The tumor stained with synaptophysin, chromogranin, and calcitonin. Thyrogloblulin was negative.
Left: H&E; Right: Calcitonin
cross section: human parathythyroid gland
magnification: 100x
hematoxylin eosin stain
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Gross photo showing a large encapsulated thyroid tumor with lobulated and mahogany brown cut surface. There are visible small whitish dots on the cut surface, representing calcifications of the tumor. Jian-Hua Qiao, MD, FCAP, Los Angeles, CA, USA. (乔建华医学博士， 美国病理学家学院专家会员。美国加州洛杉矶)
cross section: human parathythyroid gland
magnification: 100x phase contrast
hematoxylin eosin stain
Technical Questions:bioimagesoer@gmail.com