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A giant grouper at the Georgia Aquarium, seen swimming among schools of other fish
A giant grouper at the Georgia Aquarium, seen swimming among schools of other fish
The ornate lionfish as seen from a head-on view
The ornate lionfish as seen from a head-on view
Scientific classification
Kingdom: Animalia
Phylum: Chordata
(unranked) Craniata
Included groups
Jawless fishes
Armoured fishes (extinct)
Cartilaginous fishes
Ray-finned fishes
Lobe-finned fishes
Excluded groups


A fish is any aquatic vertebrate animal that is covered with scales, and equipped with two sets of paired fins and several unpaired fins. Most fish are ectothermic (or cold-blooded). Fish are abundant in most bodies of water. Fish can be found in high mountain streams (e.g., char and gudgeon) and in the deepest ocean depths (e.g., gulpers and anglerfish). According to FishBase, 31,500 species of fishes had been described by January 2010.[1]

Food prepared from fish is also called fish, and is an important human food source. Commercial and subsistence fishers "hunt" them in wild fisheries (see fishing) or "farm" them in ponds or in cages in the ocean (see aquaculture). They are also caught by recreational fishers and raised by fishkeepers, and are exhibited in public aquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies.


Diversity of fish

The term "fish" most precisely describes any non-tetrapod craniate (i.e. an animal with a skull and in most cases a backbone) that has gills throughout life and whose limbs, if any, are in the shape of fins.[2] Unlike groupings such as birds or mammals, fish are not a single clade but a paraphyletic collection of taxa, including hagfishes, lampreys, sharks and rays, ray-finned fishes, coelacanths, and lungfishes.[3][4]

A typical fish is ectothermic, has a streamlined body for rapid swimming, extracts oxygen from water using gills or uses an accessory breathing organ to breathe atmospheric oxygen, has two sets of paired fins, usually one or two (rarely three) dorsal fins, an anal fin, and a tail fin, has jaws, has skin that is usually covered with scales, and lays eggs.

Photo of fish with many narrow, straight appendages. Some are end in points, and others are longer, ending in two or three approximately flat, triangular flaps, each with a dark spot.
Fish come in many shapes and sizes. This is a sea dragon, a close relative of the seahorse. Their leaf-like appendages enable them to blend in with floating seaweed.

Each criterion has exceptions. Tuna, swordfish, and some species of sharks show some warm-blooded adaptations—they can heat their bodies significantly above ambient water temperature.[3] Streamlining and swimming performance varies from fish such as tuna, salmon, and jacks that can cover 10–20 body-lengths per second to species such as eels and rays that swim no more than 0.5 body-lengths per second.[3] Many groups of freshwater fish extract oxygen from the air as well as from the water using a variety of different structures. Lungfish have paired lungs similar to those of tetrapods, gouramis have a structure called the labyrinth organ that performs a similar function, while many catfish, such as Corydoras extract oxygen via the intestine or stomach.[5] Body shape and the arrangement of the fins is highly variable, covering such seemingly un-fishlike forms as seahorses, pufferfish, anglerfish, and gulpers. Similarly, the surface of the skin may be naked (as in moray eels), or covered with scales of a variety of different types usually defined as placoid (typical of sharks and rays), cosmoid (fossil lungfishes and coelacanths), ganoid (various fossil fishes but also living gars and bichirs), cycloid, and ctenoid (these last two are found on most bony fish).[6] There are even fishes that live mostly on land. Mudskippers feed and interact with one another on mudflats and go underwater to hide in their burrows.[7] The catfish Phreatobius cisternarum lives in underground, phreatic habitats, and a relative lives in waterlogged leaf litter.[8][9]

Fish range in size from the huge 16 metres (52 ft) whale shark to the tiny 8 millimetres (0.31 in) stout infantfish.

Many types of aquatic animals commonly referred to as "fish" are not fish in the sense given above; examples include shellfish, cuttlefish, starfish, crayfish and jellyfish. In earlier times, even biologists did not make a distinction – sixteenth century natural historians classified also seals, whales, amphibians, crocodiles, even hippopotamuses, as well as a host of aquatic invertebrates, as fish.[10] In some contexts, especially in aquaculture, the true fish are referred to as finfish (or fin fish) to distinguish them from these other animals.


Fish are a paraphyletic group: that is, any clade containing all fish also contains the tetrapods, which are not fish. For this reason, groups such as the "Class Pisces" seen in older reference works are no longer used in formal classifications.

Fish are classified into the following major groups:

Some palaeontologists contend that because Conodonta are chordates, they are primitive fish. For a fuller treatment of this taxonomy, see the vertebrate article.

The various fish groups account for more than half of vertebrate species. There are almost 28,000 known extant species, of which almost 27,000 are bony fish, with 970 sharks, rays, and chimeras and about 108 hagfishes and lampreys.[11] A third of these species fall within the nine largest families; from largest to smallest, these families are Cyprinidae, Gobiidae, Cichlidae, Characidae, Loricariidae, Balitoridae, Serranidae, Labridae, and Scorpaenidae. About 64 families are monotypic, containing only one species. The final total of extant species may grow to exceed 32,500.[12]


The anatomy of Lampanyctodes hectoris
(1) – operculum (gill cover), (2) – lateral line, (3) – dorsal fin, (4) – fat fin, (5) – caudal peduncle, (6) – caudal fin, (7) – anal fin, (8) – photophores, (9) – pelvic fins (paired), (10) – pectoral fins (paired)


Most fish exchange gases using gills on either side of the pharynx. Gills consist of threadlike structures called filaments. Each filament contains a capillary network that provides a large surface area for exchanging oxygen and carbon dioxide. Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. In some fishes, capillary blood flows in the opposite direction to the water, causing counter current exchange. The gills push the oxygen-poor water out through openings in the sides of the pharynx. Some fishes, like sharks and lampreys, possess multiple gill openings. However, most fishes have a single gill opening on each side. This opening is hidden beneath a protective bony cover called an operculum.

Juvenile bichirs have external gills, a very primitive feature that they share with larval amphibians.

Photo of white bladder that consists of a rectangular section and a banana-shaped section connectd by a much thinner element
Swim bladder of a Rudd (Scardinius erythrophthalmus)

Many fish can breathe air via a variety of mechanisms. The skin of anguillid eels may absorb oxygen. The buccal cavity of the electric eel may breathe air. Catfishes of the families Loricariidae, Callichthyidae, and Scoloplacidae absorb air through their digestive tracts.[13] Lungfish and bichirs have paired lungs similar to those of tetrapods and must surface to gulp fresh air through the mouth and pass spent air out through the gills. Gar and bowfin have a vascularized swim bladder that functions in the same way. Loaches, trahiras, and many catfish breathe by passing air through the gut. Mudskippers breathe by absorbing oxygen across the skin (similar to frogs). A number of fishes have evolved so-called accessory breathing organs that extract oxygen from the air. Labyrinth fish (such as gouramis and bettas) have a labyrinth organ above the gills that performs this function. A few other fish have structures resembling labyrinth organs in form and function, most notably snakeheads, pikeheads, and the Clariidae catfish family.

Breathing air is primarily of use to fish that inhabit shallow, seasonally variable waters where the water's oxygen concentration may seasonally decline. Fishes dependent solely on dissolved oxygen, such as perch and cichlids, quickly suffocate, while air-breathers survive for much longer, in some cases in water that is little more than wet mud. At the most extreme, some air-breathing fish are able to survive in damp burrows for weeks without water, entering a state of aestivation (summertime hibernation) until water returns.

Photo of fish head split in half longitudinally with gill filaments crossing from top to bottom
Tuna gills inside of the head. The fish head is oriented snout-downwards, with the view looking towards the mouth.

Fish can be divided into obligate air breathers and facultative air breathers. Obligate air breathers, such as the African lungfish, must breathe air periodically or they suffocate. Facultative air breathers, such as the catfish Hypostomus plecostomus, only breathe air if they need to and will otherwise rely on their gills for oxygen. Most air breathing fish are facultative air breathers that avoid the energetic cost of rising to the surface and the fitness cost of exposure to surface predators.[13]


Fish have a closed-loop circulatory system. The heart pumps the blood in a single loop throughout the body. In most fish, the heart consists of four parts, including two chambers and an entrance and exit.[14] The first part is the sinus venosus, a thin-walled sac that collects blood from the fish's veins before allowing it to flow to the second part, the atrium, which is a large muscular chamber. The atrium serves as a one-way antechamber, sends blood to the third part, ventricle. The ventricle is another thick-walled, muscular chamber and it pumps the blood, first to the fourth part, bulbous arteriosus, a large tube, and then out of the heart. The bulbus arteriosus connects to the aorta, through which blood flows to the gills for oxygenation.


Jaws allow fish to eat a wide variety of food, including plants and other organisms. Fish ingest food through the mouth and break it down in the esophagus. In the stomach, food is further digested and, in many fish, processed in finger-shaped pouches called pyloric caeca, which secrete digestive enzymes and absorb nutrients. Organs such as the liver and pancreas add enzymes and various chemicals as the food moves through the digestive tract. The intestine completes the process of digestion and nutrient absorption.


As with many aquatic animals, most fish release their nitrogenous wastes as ammonia. Some of the wastes diffuse through the gills. Blood wastes are filtered by the kidneys.

Saltwater fish tend to lose water because of osmosis. Their kidneys return water to the body. The reverse happens in freshwater fish: they tend to gain water osmotically. Their kidneys produce dilute urine for excretion. Some fish have specially adapted kidneys that vary in function, allowing them to move from freshwater to saltwater.


The scales of fish originate from the mesoderm (skin); they may be similar in structure to teeth.

Sensory and nervous system

Anatomical diagram showing the pairs of olfactory, telencephalon, and optic lobes, followed by the cerebellum and the mylencephalon
Dorsal view of the brain of the rainbow trout

Central nervous system

Fish typically have quite small brains relative to body size compared with other vertebrates, typically one-fifteenth the brain mass of a similarly sized bird or mammal.[15] However, some fish have relatively large brains, most notably mormyrids and sharks, which have brains about as massive relative to body weight as birds and marsupials.[16]

Fish brains are divided into several regions. At the front are the olfactory lobes, a pair of structures that receive and process signals from the nostrils via the two olfactory nerves.[15] The olfactory lobes are very large in fishes that hunt primarily by smell, such as hagfish, sharks, and catfish. Behind the olfactory lobes is the two-lobed telencephalon, the structural equivalent to the cerebrum in higher vertebrates. In fishes the telencephalon is concerned mostly with olfaction.[15] Together these structures form the forebrain.

Connecting the forebrain to the midbrain is the diencephalon (in the diagram, this structure is below the optic lobes and consequently not visible). The diencephalon performs functions associated with hormones and homeostasis.[15] The pineal body lies just above the diencephalon. This structure detects light, maintains circadian rhythms, and controls color changes.[15]

The midbrain or mesencephalon contains the two optic lobes. These are very large in species that hunt by sight, such as rainbow trout and cichlids.[15]

The hindbrain or metencephalon is particularly involved in swimming and balance.[15] The cerebellum is a single-lobed structure that is typically the biggest part of the brain.[15] Hagfish and lampreys have relatively small cerebellae, while the mormyrid cerebellum is massive and apparently involved in their electrical sense.[15]

The brain stem or myelencephalon is the brain's posterior.[15] As well as controlling some muscles and body organs, in bony fish at least, the brain stem governs respiration and osmoregulation.[15]

Sense organs

Most fish possess highly developed sense organs. Nearly all daylight fish have color vision that is at least as good as a human's. Many fish also have chemoreceptors that are responsible for extraordinary senses of taste and smell. Although they have ears, many fish may not hear very well. Most fish have sensitive receptors that form the lateral line system, which detects gentle currents and vibrations, and senses the motion of nearby fish and prey.[17] Some fish, such as catfish and sharks, have organs that detect low-level electric current.[18] Other fish, like the electric eel, can produce electric current.

Fish orient themselves using landmarks and may use mental maps based on multiple landmarks or symbols. Fish behavior in mazes reveals that they possess spatial memory and visual discrimination.[19]

Capacity for pain

Experiments done by William Tavolga provide evidence that fish have pain and fear responses. For instance, in Tavolga’s experiments, toadfish grunted when electrically shocked and over time they came to grunt at the mere sight of an electrode.[20]

In 2003, Scottish scientists at the University of Edinburgh and the Roslin Institute concluded that rainbow trout exhibit behaviors often associated with pain in other animals. Bee venom and acetic acid injected into the lips resulted in fish rocking their bodies and rubbing their lips along the sides and floors of their tanks, which the researchers concluded were attempts to relieve pain, similar to what mammals would do.[21][22][23] Neurons fired in a pattern resembling human neuronal patterns.[23]

Professor James D. Rose of the University of Wyoming claimed the study was flawed since it did not provide proof that fish possess "conscious awareness, particularly a kind of awareness that is meaningfully like ours".[24] Rose argues that since fish brains are so different from human brains, fish are probably not conscious in the manner humans are, so that reactions similar to human reactions to pain instead have other causes. Rose had published a study a year earlier arguing that fish cannot feel pain because their brains lack a neocortex.[25] However, animal behaviorist Temple Grandin argues that fish could still have consciousness without a neocortex because "different species can use different brain structures and systems to handle the same functions."[23]

Animal welfare advocates raise concerns about the possible suffering of fish caused by angling. Some countries, such as Germany have banned specific types of fishing, and the British RSPCA now formally prosecutes individuals who are cruel to fish.[26]

Muscular system

Most fish move by alternately contracting paired sets of muscles on either side of the backbone. These contractions form S-shaped curves that move down the body. As each curve reaches the back fin, backward force is applied to the water, and in conjunction with the fins, moves the fish forward. The fish's fins function like an airplane's flaps. Fins also increase the tail's surface area, increasing speed. The streamlined body of the fish decreases the amount of friction from the water. Since body tissue is denser than water, fish must compensate for the difference or they will sink. Many bony fishes have an internal organ called a swim bladder that adjusts their buoyancy through manipulation of gases.


Photo of shark surrounded by school of other fish
A 3-tonne (3.0 LT; 3.3 ST) great white shark off Isla Guadalupe

Although most fish are exclusively aquatic and ectothermic, there are exceptions to both cases.

Fish from multiple groups can live out of the water for extended time periods. Amphibious fish such as the mudskipper can live and move about on land for up to several days.

Certain species of fish maintain elevated body temperatures. Endothermic teleosts (bony fishes) are all in the suborder Scombroidei and include the billfishes, tunas, and one species of "primitive" mackerel (Gasterochisma melampus). All sharks in the family Lamnidae – shortfin mako, long fin mako, white, porbeagle, and salmon shark – are endothermic, and evidence suggests the trait exists in family Alopiidae (thresher sharks). The degree of endothermy varies from the billfish, which warm only their eyes and brain, to bluefin tuna and porbeagle sharks who maintain body temperatures elevated in excess of 20 °C above ambient water temperatures. See also gigantothermy. Endothermy, though metabolically costly, is thought to provide advantages such as increased muscle strength, higher rates of central nervous system processing, and higher rates of digestion.

Reproductive system


Organs: 1. Liver, 2. Gas bladder, 3. Roe, 4. Pyloric caeca, 5. Stomach, 6. Intestine

Fish reproductive organs include testes and ovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused.[27] There may also be a range of secondary organs that increase reproductive fitness.

In terms of spermatogonia distribution, the structure of teleosts testes has two types: in the most common, spermatogonia occur all along the seminiferous tubules, while in Atherinomorph fishes they are confined to the distal portion of these structures. Fishes can present cystic or semi-cystic spermatogenesis in relation to the release phase of germ cells in cysts to the seminiferous tubules lumen.[27]

Fish ovaries may be of three types: gymnovarian, secondary gymnovarian or cystovarian. In the first type, the oocytes are released directly into the coelomic cavity and then enter the ostium, then through the oviduct and are eliminated. Secondary gymnovarian ovaries shed ova into the coelom from which they go directly into the oviduct. In the third type, the oocytes are conveyed to the exterior through the oviduct.[28] Gymnovaries are the primitive condition found in lungfish, sturgeon, and bowfin. Cystovaries characterize most teleosts, where the ovary lumen has continuity with the oviduct.[27] Secondary gymnovaries are found in salmonids and a few other teleosts.

Oogonia development in teleosts fish varies according to the group, and the determination of oogenesis dynamics allows the understanding of maturation and fertilization processes. Changes in the nucleus, ooplasm, and the surrounding layers characterize the oocyte maturation process.[27]

Postovulatory follicles are structures formed after oocyte release; they do not have endocrine function, present a wide irregular lumen, and are rapidly reabosrbed in a process involving the apoptosis of follicular cells. A degenerative process called follicular atresia reabsorbs vitellogenic oocytes not spawned. This process can also occur, but less frequently, in oocytes in other development stages.[27]

Some fish are hermaphrodites, having both testes and ovaries either at different phases in their life cycle or, as in hamlets, have them simultaneously.

Reproductive method

Over 97% of all known fishes are oviparous,[29] that is, the eggs develop outside the mother's body. Examples of oviparous fishes include salmon, goldfish, cichlids, tuna, and eels. In the majority of these species, fertilization takes place outside the mother's body, with the male and female fish shedding their gametes into the surrounding water. However, a few oviparous fishes practice internal fertilization, with the male using some sort of intromittent organ to deliver sperm into the genital opening of the female, most notably the oviparous sharks, such as the horn shark, and oviparous rays, such as skates. In these cases, the male is equipped with a pair of modified pelvic fins known as claspers.

Marine fish can produce high numbers of eggs which are often released into the open water column. The eggs have an average diameter of 1 millimetre (0.039 in).

Photo of semi-transparent creature with a darker, yolk-like central structure and other approximately-round internal elements
An example of zooplankton

The newly-hatched young of oviparous fish are called larvae. They are usually poorly formed, carry a large yolk sac (for nourishment) and are very different in appearance from juvenile and adult specimens. The larval period in oviparous fish is relatively short (usually only several weeks), and larvae rapidly grow and change appearance and structure (a process termed metamorphosis) to become juveniles. During this transition larvae must switch from their yolk sac to feeding on zooplankton prey, a process which depends on typically inadequate zooplankton density, starving many larvae.

In ovoviviparous fish the eggs develop inside the mother's body after internal fertilization but receive little or no nourishment directly from the mother, depending instead on the yolk. Each embryo develops in its own egg. Familiar examples of ovoviviparous fishes include guppies, angel sharks, and coelacanths.

Some species of fish are viviparous. In such species the mother retains the eggs and nourishes the embryos. Typically, viviparous fishes have a structure analogous to the placenta seen in mammals connecting the mother's blood supply with the that of the embryo. Examples of viviparous fishes include the surf-perches, splitfins, and lemon shark. Some viviparous fishes exhibit oophagy, in which the developing embryos eat other eggs produced by the mother. This has been observed primarily among sharks, such as the shortfin mako and porbeagle, but is known for a few bony fish as well, such as the halfbeak Nomorhamphus ebrardtii.[30] Intrauterine cannibalism is an even more unusual mode of vivipary, in which the largest embryos eat weaker and smaller siblings. This behavior is also most commonly found among sharks, such as the grey nurse shark, but has also been reported for Nomorhamphus ebrardtii.[30]

Aquarists commonly refer to ovoviviparous and viviparous fishes as livebearers.

Immune system

Immune organs vary by type of fish.[31] In the jawless fish (lampreys and hagfishes), true lymphoid organs are absent. These fish rely on regions of lymphoid tissue within other organs to produce immune cells. For example, erythrocytes, macrophages and plasma cells are produced in the anterior kidney (or pronephros) and some areas of the gut (where granulocytes mature.) They resemble primitive bone marrow in hagfish. Cartilaginous fish (sharks and rays) have a more advanced immune system. They have three specialized organs that are unique to chondrichthyes; the epigonal organs (lymphoid tissue similar to mammalian bone) that surround the gonads, the Leydig's organ within the walls of their esophagus, and a spiral valve in their intestine. These organs house typical immune cells (granulocytes, lymphocytes and plasma cells). They also possess an identifiable thymus and a well-developed spleen (their most important immune organ) where various lymphocytes, plasma cells and macrophages develop and are stored. Chondrostean fish (sturgeons, paddlefish and birchirs) possess a major site for the production of granulocytes within a mass that is associated with the meninges (membranes surrounding the central nervous system.) Their heart is frequently covered with tissue that contains lymphocytes, reticular cells and a small number of macrophages. The chondrostean kidney is an important hemopoietic organ; where erythrocytes, granulocytes, lymphocytes and macrophages develop.

Like chondrostean fish, the major immune tissues of bony fish (or teleostei) include the kidney (especially the anterior kidney), which houses many different immune cells.[32] In addition, teleost fish possess a thymus, spleen and scattered immune areas within mucosal tissues (e.g. in the skin, gills, gut and gonads). Much like the mammalian immune system, teleost erythrocytes, neutrophils and granulocytes are believed to reside in the spleen whereas lymphocytes are the major cell type found in the thymus.[33][34] In 2006, a lymphatic system similar to that in mammals was described in one species of teleost fish, the zebrafish. Although not confirmed as yet, this system presumably will be where naive (unstimulated) T cells accumulate while waiting to encounter an antigen.[35]


Like other animals, fish suffer from diseases and parasites. To prevent disease they have a variety of defenses. Non-specific defenses include the skin and scales, as well as the mucus layer secreted by the epidermis that traps and inhibits the growth of microorganisms. Should pathogens breach these defenses, fish can develop an inflammatory response that increases blood flow to the infected region and delivers white blood cells that attempt to destroy pathogens. Specific defenses respond to particular pathogens recognised by the fish's body, i.e., an immune response.[36] In recent years, vaccines have become widely used in aquaculture and also with ornamental fish, for example furunculosis vaccines in farmed salmon and koi herpes virus in koi.[37][38]


Some species use cleaner fish to remove external parasites. The best known of these are the Bluestreak cleaner wrasses of the genus Labroides found on coral reefs in the Indian and Pacific Oceans. These small fish maintain so-called "cleaning stations" where other fish congregate and perform specific movements to attract the attention of the cleaners.[39] Cleaning behaviors have been observed in a number of fish groups, including an interesting case between two cichlids of the same genus, Etroplus maculatus, the cleaner, and the much larger Etroplus suratensis.[40]


Animation showing life at different evolutionary stages
Outdated evolutionary view of continual gradation
Drawing of animal with large mouth, long tail, very small dorsal fins, and pectoral fins that attach towards the bottom of the body, resembling lizard legs in scale and development.[41]
Dunkleosteus was a gigantic, 10 meter (33 ft) long prehistoric fish.

Since Fish is not a monophyletic group, dealing of its evolution is not practiced anymore[42].

Proliferation was apparently due to the hinged jaw, because jawless fish left very few descendants.[43] Lampreys may approximate pre-jawed fish. The first jaws are found in Placodermi fossils. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination.

Fish may have evolved from a creature similar to a coral-like Sea squirt, whose larvae resemble primitive fish in important ways. Fish' first ancestors may have kept the larval form into adulthood (as some sea squirts do today), although perhaps the reverse is the case. Candidates for early fish include Agnatha such as Haikouichthys, Myllokunmingia and Conodonts.[citation needed]

Importance to humans

Economic importance



Photo of shark in profile surrounded by other, much smaller fish in bright sunlight
A Whale shark, the world's largest fish, is classified as Vulnerable.

The 2006 IUCN Red List names 1,173 fish species that are threatened with extinction.[44] Included are species such as Atlantic cod,[45] Devil's Hole pupfish,[46] coelacanths,[47] and great white sharks.[48] Because fish live underwater they are more difficult to study than terrestrial animals and plants, and information about fish populations is often lacking. However, freshwater fish seem particularly threatened because they often live in relatively small water bodies. For example, the Devil's Hole pupfish occupies only a single 3 by 6 metres (9.8 by 20 ft) pool.[49]


Overfishing is a major threat to edible fishes such as cod and tuna.[50][51] Overfishing eventually causes population (known as stock) collapse because the survivors cannot produce enough young to replace those removed. Such commercial extinction does not mean that the species is extinct, merely that it can no longer sustain a fishery.

One well-studied example of fishery collapse is the Pacific sardine Sadinops sagax caerulues fishery off the California coast. From a 1937 peak of 790,000 long tons (800,000 t) the catch steadily declined to only 24,000 long tons (24,000 t) in 1968, after which the fishery was no longer economically viable.[52]

The main tension between fisheries science and the fishing industry is that the two groups have different views on the resiliency of fisheries to intensive fishing. In places such as Scotland, Newfoundland, and Alaska the fishing industry is a major employer, so governments are predisposed to support it.[53][54] On the other hand, scientists and conservationists push for stringent protection, warning that many stocks could be wiped out within fifty years.[55][56]

Habitat destruction

A key stress on both freshwater and marine ecosystems is habitat degradation including water pollution, the building of dams, removal of water for use by humans, and the introduction of exotic species.[57] An example of a fish that has become endangered because of habitat change is the pallid sturgeon, a North American freshwater fish that lives in rivers damaged by human activity.[58]

Exotic species

Introduction of non-native species has occurred in many habitats. One of the best studied examples is the introduction of Nile perch into Lake Victoria in the 1960s. Nile perch gradually exterminated the lake's 500 endemic cichlid species. Some of them survive now in captive breeding programmes, but others are probably extinct.[59] Carp, snakeheads,[60] tilapia, European perch, brown trout, rainbow trout, and sea lampreys are other examples of fish that have caused problems by being introduced into alien environments.

Aquarium collecting


In the Book of Jonah a "great fish" swallowed Jonah the Prophet. Legends of half-human, half-fish mermaids have featured in stories like those of Hans Christian Andersen and movies like Splash (See Merman, Mermaid).

Among the deities said to take the form of a fish are Ika-Roa of the Polynesians, Dagon of various ancient Semitic peoples, the shark-gods of [Hawaiʻ and Matsya of the Dravidas of India. The astrological symbol Pisces is based on a constellation of the same name, but there is also a second fish constellation in the night sky, Piscis Austrinus.

Fish have been used figuratively in many different ways, for example the ichthys used by early Christians to identify themselves, through to the fish as a symbol of fertility among Bengalis.[61]

Drawing of vertical fish below a 5-pointed golden crown and surrounded by other golden objects
Coat of arms of Comacchio, Italy
Drawing of two swords and two fish in profile on background with rectangular top and angled-bottom
coat of arms of Narva, Estonia

Fish feature prominently in art and literature, in movies such as Finding Nemo and books such as The Old Man and the Sea. Large fish, particularly sharks, have frequently been the subject of horror movies and thrillers, most notably the novel Jaws, which spawned a series of films of the same name that in turn inspired similar films or parodies such as Shark Tale, Snakehead Terror, and Piranha.

In the semiotic of Ashtamangala (buddhist symbolism) the golden fish (Sanskrit: Matsya), represents the state of fearless suspension in samsara, perceived as the harmless ocean, referred to as 'buddha-eyes' or 'rigpa-sight'. The fish symbolizes the auspiciousness of all living beings in a state of fearlessness without danger of drowning in the Samsaric Ocean of Suffering, and migrating from teaching to teaching freely and spontaneously just as fish swim.

Drawing of three men sitting on fish at the surface, each wearing a sailor suit and waving a flag
Fish riders in a 1920s poster of the Republic of China.

They have religious significance in Hindu, Jain and Buddhist traditions but also in Christianity who is first signified by the sign of the fish, and especially referring to feeding the multitude in the desert. In the dhamma of Buddha the fish symbolize happiness as they have complete freedom of movement in the water. They represent fertility and abundance. Often drawn in the form of carp which are regarded in the Orient as sacred on account of their elegant beauty, size and life-span.[3]

The name of the Canadian city of Coquitlam, British Columbia is derived from Kwikwetlem, which is said to be derived from a Coast Salish term meaning "little red fish".[62]


Fish or fishes

Though often used interchangeably, these words have different meanings. Fish is used either as singular noun or to describe a group of specimens from a single species. Fishes describes a group of different species.[3]

Shoal or school

Photo of thousands of fish separated from each other by distances of 2 inches (51 mm) or less
These goldband fusiliers are schooling because their swimming is synchronised

A random assemblage of fishes merely using some localised resource such as food or nesting sites is known simply as an aggregation. When fish come together in an interactive, social grouping, then they may be forming either a shoal or a school depending on the degree of organisation. A shoal is a loosely organised group where each fish swims and forages independently but is attracted to other members of the group and adjusts its behaviour, such as swimming speed, so that it remains close to the other members of the group. Schools of fish are much more tightly organised, synchronising their swimming so that all fish move at the same speed and in the same direction. Shoaling and schooling behaviour is believed to provide a variety of advantages.[63]


  • Cichlids congregating at lekking sites form an aggregation.
  • Many minnows and characins form shoals.
  • Anchovies, herrings, and silversides are classic examples of schooling fishes.

While school and shoal have different meanings within biology, they are often treated as synonyms by non-specialists, with speakers of British English using "shoal" to describe any grouping of fish, while speakers of American English often using "school" just as loosely.

See also

For a topical guide to sharks, see Outline of sharks


  1. ^ FishBase: April 2009 Update. Retrieved 10 April 2010.
  2. ^ Nelson, Joseph S. (2006). Fishes of the World. John Wiley & Sons, Inc.. p. 2. ISBN 0471250317. 
  3. ^ a b c d The Diversity of Fishes, Blackwell Publishing. 1997. p. 3. ISBN 0-86542-256-7. 
  4. ^ Tree of life web project – Chordates.
  5. ^ The Diversity of Fishes, Blackwell Publishing. 1997. pp. 53–57. ISBN 0-86542-256-7. 
  6. ^ The Diversity of Fishes, Blackwell Publishing. 1997. pp. 33–36. ISBN 0-86542-256-7. 
  7. ^ Froese, R. and D. Pauly. Editors.. "Species Summary: Periophthalmus barbarus". FishBase. Retrieved 26 November 2006. 
  8. ^ Froese, R. and D. Pauly. Editors.. "Species Summary: Phreatobius cisternarum". FishBase. Retrieved 26 November 2006. 
  9. ^ Planet Catfish. "Cat-eLog: Heptapteridae: Phreatobius: Phreatobius sp. (1)". Planet Catfish. Retrieved 26 November 2006. 
  10. ^ Jr.Cleveland P Hickman, Larry S. Roberts, Allan L. Larson: Integrated Principles of Zoology, McGraw-Hill Publishing Co, 2001, ISBN 0–07–290961–7
  11. ^ Nelson, J. S.: Fishes of the World, John Wiley & Sons, Inc., pp. 4–5, 2006 ISBN 0471250317
  12. ^ Nelson, J. S.: Fishes of the World, John Wiley & Sons, Inc., p 3, 2006 ISBN 0471250317
  13. ^ a b "Modifications of the Digestive Tract for Holding Air in Loricariid and Scoloplacid Catfishes" (PDF). Copeia (3): 663–675. 1998. Retrieved 25 June 2009. 
  14. ^ Setaro, John F. (1999). Circulatory System. Microsoft Encarta 99. 
  15. ^ a b c d e f g h i j k Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, p. 48–49, 1997, ISBN 0-86542-256-7
  16. ^ Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, p 191, 1997, ISBN 0-86542-256-7
  17. ^ Orr, James (1999). Fish. Microsoft Encarta 99. 
  18. ^ Albert, J.S., and W.G.R. Crampton. 2005. Electroreception and electrogenesis. pp. 431–472 in The Physiology of Fishes, 3rd Edition. D.H. Evans and J.B. Claiborne (eds.). CRC Press.
  19. ^ Journal of Undergraduate Life Sciences. "Appropriate maze methodology to study learning in fish" (PDF). Retrieved 28 May 2009. 
  20. ^ Dunayer, Joan, "Fish: Sensitivity Beyond the Captor's Grasp," The Animals' Agenda, July/August 1991, pp. 12–18
  21. ^ Vantressa Brown, “Fish Feel Pain, British Researchers Say,” Agence France-Presse, 1 May 2003
  22. ^ "Fish do feel pain, scientists say". BBC News. 30 April 2003. Retrieved 4 January 2010. 
  23. ^ a b c Grandin, Temple; Johnson, Catherine (2005). Animals in Translation. New York, New York: Scribner. pp. 183–184. ISBN 0743247698. 
  24. ^ Rose, J.D. 2003. A Critique of the paper: "Do fish have nociceptors: Evidence for the evolution of a vertebrate sensory system"</
  25. ^ James D. Rose, Do Fish Feel Pain?, 2002. Retrieved September 27, 2007.
  26. ^ Leake, J. “Anglers to Face RSPCA Check,” The Sunday Times – Britain, 14 March 2004
  27. ^ a b c d e Guimaraes-Cruz, Rodrigo J.; Santos, José E. dos; Santos, Gilmar B. (July/Sept. 2005). "Gonadal structure and gametogenesis of Loricaria lentiginosa Isbrücker (Pisces, Teleostei, Siluriformes)". Rev. Bras. Zool. 22 (3): 556–564. ISSN 0101-8175. 
  28. ^ Brito, M.F.G.; Bazzoli, N. (2003). "Reproduction of the surubim catfish (Pisces, Pimelodidae) in the São Francisco River, Pirapora Region, Minas Gerais, Brazil". Arquivo Brasileiro de Medicina Veterinária e Zootecnia 55 (5). doi:10.1590/S0102-09352003000500018. ISSN: 0102-0935. 
  29. ^ Peter Scott: Livebearing Fishes, p. 13. Tetra Press 1997. ISBN 1-5646-5193-2
  30. ^ a b Meisner, A & Burns, J: Viviparity in the Halfbeak Genera Dermogenys and Nomorhamphus (Teleostei: Hemiramphidae). Journal of Morphology 234, pp. 295–317, 1997
  31. ^ A.G. Zapata, A. Chiba and A. Vara. Cells and tissues of the immune system of fish. In: The Fish Immune System: Organism, Pathogen and Environment. Fish Immunology Series. (eds. G. Iwama and T.Nakanishi,), New York, Academic Press, 1996, pp. 1–55.
  32. ^ D.P. Anderson. Fish Immunology. (S.F. Snieszko and H.R. Axelrod, eds), Hong Kong: TFH Publications, Inc. Ltd., 1977.
  33. ^ S. Chilmonczyk. The thymus in fish: development and possible function in the immune response. Annual Review of Fish Diseases, Volume 2, 1992, pp. 181–200.
  34. ^ J.D. Hansen and A.G. Zapata. Lymphocyte development in fish and amphibians. Immunological Reviews, Volume 166, 1998, pp. 199–220.
  35. ^ Kucher et al.,. Development of the zebrafish lymphatic system requires VegFc signalling. Current Biology, Volume 16, 2006, pp. 1244–1248.
  36. ^ Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, pp. 95–96, 1997, ISBN 0-86542-256-7
  37. ^ R. C. Cipriano (2001), Furunculosis And Other Diseases Caused By Aeromonas salmonicida. Fish Disease Leaflet 66. U.S. Department of the Interior.[1]
  38. ^ K H Hartman et al. (2004), Koi Herpes Virus (KHV) Disease. Fact Sheet VM-149. University of Florida Institute of Food and Agricultural Sciences.[2]
  39. ^ Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, p 380, 1997, ISBN 0-86542-256-7
  40. ^ Richard L. Wyman and Jack A. Ward (1972). A Cleaning Symbiosis between the Cichlid Fishes Etroplus maculatus and Etroplus suratensis. I. Description and Possible Evolution. Copeia, Vol. 1972, No. 4, pp. 834–838.
  41. ^ Monster fish crushed opposition with strongest bite ever,
  42. ^ G. Lecointre & H. Le Guyader, 2007, The Tree of Life: A Phylogenetic Classification, Harvard University Press Reference Library
  43. ^ Classification of the Chordates Evolution, ecology and biodiversity 05-1116-3, University of Winnipeg. Retrieved 7 April 2007.
  44. ^ "Table 1: Numbers of threatened species by major groups of organisms (1996–2004)". Retrieved 18 January 2006. 
  45. ^ "Gadus morhua". Retrieved 18 January 2006. 
  46. ^ "Cyprinodon diabolis". Retrieved 18 January 2006. 
  47. ^ "Latimeria chalumnae". Retrieved 18 January 2006. 
  48. ^ "Carcharodon carcharias". Retrieved 18 January 2006. 
  49. ^ Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, pp. 449–450, 1997, ISBN 0-86542-256-7
  50. ^ "Call to halt cod 'over-fishing'". BBC News. 5 January 2007. Retrieved 18 January 2006. 
  51. ^ "Tuna groups tackle overfishing". BBC News. 26 January 2007. Retrieved 18 January 2006. 
  52. ^ Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, p 462, 1997, ISBN 0-86542-256-7
  53. ^ "UK 'must shield fishing industry'". BBC News. 3 November 2006. Retrieved 18 January 2006. 
  54. ^ "EU fish quota deal hammered out". BBC News. 21 December 2006. Retrieved 18 January 2006. 
  55. ^ "Ocean study predicts the collapse of all seafood fisheries by 2050". Retrieved 13 January 2006. 
  56. ^ "Atlantic bluefin tuna could soon be commercially extinct". Retrieved 18 January 2006. 
  57. ^ Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, p 463, 1997, ISBN 0-86542-256-7
  58. ^ "Threatened and Endangered Species: Pallid Sturgeon Scaphirhynchus Fact Sheet". Retrieved 18 January 2006. 
  59. ^ "The little fish fight back".,,1541613,00.html. Retrieved 18 January 2006. 
  60. ^ "Stop That Fish!". Retrieved 26 August 2007. 
  61. ^ Jaffrey, M.: A Taste of India, Atheneum, p 148, 1988, ISBN 0-689-70726-6
  62. ^ Kwikwetlem First Nation: History & Culture Retrieved on 5 March 2009
  63. ^ Helfman G., Collette B., & Facey D.: The Diversity of Fishes, Blackwell Publishing, p 375, 1997, ISBN 0-86542-256-7


External links


Up to date as of January 14, 2010

From Wikiquote

Fish are aquatic vertebrates that are typically cold blooded, covered with scales, and equipped with two sets of paired fins and several unpaired fins.


  • Piscem natare doces
    • Translation: You're teaching a fish to swim.
    • Anonymous Latin saying
  • Fish and guests in three days are stale.
  • A man may fish with the worm that hath eat of a king, and eat of the fish that hath fed of that worm.
  • What have we here? a man or a fish? dead or alive? A fish: he smells like a fish; a very ancient and fish-like smell.
  • I am, out of the ladies' company, like a fish out of water.
  • It was always the biggest fish I caught that got away.
  • Aquarium fishes even if they only imagine going to a lake, the windows of that aquarium will become thinner than before.
  • Only the gamefish swims upstream,
    But the sensible fish swims down.
  • People would cry for the death of a bird, but never for the blood of a fish. Blessed are those who have a voice.
  • I know the human being and the fish can coexist peacefully.
    • George W. Bush, speech in Saginaw, Michigan (29 September 2000),[1] referring to a widely reported dispute in the Klamath region of Oregon between farmers with irrigation rights and Native Americans with fishing rights.
  • "'Fish?'

"'Some people like the oddest things.'" --Zaphod and Trillian in Douglas Adams' novel The Hitchhiker's Guide to the Galaxy


  • This island is made mainly of coal and surrounded by fish. Only an organizing genius could produce a shortage of coal and fish at the same time.

External links

Wikipedia has an article about:
Look up fish in Wiktionary, the free dictionary

Source material

Up to date as of January 22, 2010
(Redirected to The Fish article)

From Wikisource

The Fish
by Rupert Brooke

In a cool curving world he lies
And ripples with dark ecstasies.
The kind luxurious lapse and steal
Shapes all his universe to feel
And know and be; the clinging stream
Closes his memory, glooms his dream,
Who lips the roots o' the shore, and glides
Superb on unreturning tides.
Those silent waters weave for him
A fluctuant mutable world and dim,
Where wavering masses bulge and gape
Mysterious, and shape to shape
Dies momently through whorl and hollow,
And form and line and solid follow
Solid and line and form to dream
Fantastic down the eternal stream;
An obscure world, a shifting world,
Bulbous, or pulled to thin, or curled,
Or serpentine, or driving arrows,
Or serene slidings, or March narrows.
There slipping wave and shore are one,
And weed and mud. No ray of sun,
But glow to glow fades down the deep
(As dream to unknown dream in sleep);
Shaken translucency illumes
The hyaline of drifting glooms;
The strange soft-handed depth subdues
Drowned colour there, but black to hues,
As death to living, decomposes --
Red darkness of the heart of roses,
Blue brilliant from dead starless skies,
And gold that lies behind the eyes,
The unknown unnameable sightless white
That is the essential flame of night,
Lustreless purple, hooded green,
The myriad hues that lie between
Darkness and darkness! . . .

                              And all's one.
Gentle, embracing, quiet, dun,
The world he rests in, world he knows,
Perpetual curving. Only - grows
An eddy in that ordered falling,
A knowledge from the gloom, a calling
Weed in the wave, gleam in the mud -
The dark fire leaps along his blood;
Dateless and deathless, blind and still,
The intricate impulse works its will;
His woven world drops back; and he,
Sans providence, sans memory,
Unconscious and directly driven,
Fades to some dank sufficient heaven.

O world of lips, O world of laughter,
Where hope is fleet and thought flies after,
Of lights in the clear night, of cries
That drift along the wave and rise
Thin to the glittering stars above,
You know the hands, the eyes of love!
The strife of limbs, the sightless clinging,
The infinite distance, and the singing
Blown by the wind, a flame of sound,
The gleam, the flowers, and vast around
The horizon, and the heights above -
You know the sigh, the song of love!

But there the night is close, and there
Darkness is cold and strange and bare;
And the secret deeps are whisperless;
And rhythm is all deliciousness;
And joy is in the throbbing tide,
Whose intricate fingers beat and glide
In felt bewildering harmonies
Of trembling touch; and music is
The exquisite knocking of the blood.
Space is no more, under the mud;
His bliss is older than the sun.
Silent and straight the waters run.
The lights, the cries, the willows dim,
And the dark tide are one with him.

  Munich, March 1911

1911 encyclopedia

Up to date as of January 14, 2010
(Redirected to Database error article)

From LoveToKnow 1911

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Up to date as of January 15, 2010
(Redirected to fish article)

Definition from Wiktionary, a free dictionary

See also FISH



Wikipedia has an article on:


A Fish (Coho Salmon)


Etymology 1

From Old English fisc < Proto-Germanic *fiskaz < Proto-Indo-European *peisk-, *pisk-. Cognate with Dutch vis, German Fisch, Swedish fisk. The Indo-European root is also the source of Latin piscis, Russian пискарь, Irish iasc.



collectively (UK) fish or (US) and when referring to two or more kinds fishes or informally fishies

fish (collectively (UK) fish or (US) and when referring to two or more kinds fishes or informally fishies)

  1. (countable) A cold-blooded vertebrate animal that lives in water, moving with the help of fins and breathing with gills.
    Salmon is a fish.
    God created all the fishes of the world.
  2. (collectively) Plural form of fish.
    We have many fish in our aquarium.
  3. (possibly archaic) Any vertebrate that lives in water and cannot live outside it.
  4. (uncountable) The flesh of the fish used as food.
    The seafood pasta had lots of fish but not enough pasta.
  5. (countable) A period of time spent fishing.
    The fish at the lake didn't prove successful.
  6. (countable) An instance of seeking something.
    Merely two fishes for information told the whole story.
  7. (uncountable) A card game in which the object is to obtain pairs of cards.
  8. (uncountable, derogatory, slang) Women.
  9. (slang) An easy victim for swindling.
  10. (nautical) A makeshift overlapping longitudinal brace used to temporarily repair or extend a spar or mast of a ship.
Derived terms
See also
The translations below need to be checked and inserted above into the appropriate translation tables, removing any numbers. Numbers do not necessarily match those in definitions. See instructions at Help:How to check translations.


fish (not comparable)


not comparable

none (absolute)

  1. Of or relating to fish.
    It was a fine fish dinner.

Etymology 2

From Old English fiscian.


fish (not comparable)


not comparable

none (absolute)

  1. (Can we verify(+) this sense?) Of or relating to fishing.
    Put the worm on a fish hook.


to fish

Third person singular

Simple past

Past participle

Present participle

to fish (third-person singular simple present fishes, present participle fishing, simple past and past participle fished)

  1. (intransitive) To try to catch fish, whether successfully or not.
    She went to the river to fish for trout.
  2. (transitive) To try to catch fish, or to find something else, in (a body of water).
    They fished the surrounding lakes for the dead body.
  3. (intransitive, followed by "about," "around," "through," etc.) To attempt to find or get hold of an object by searching among other objects.
    Why are you fishing through in my things?
  4. (intransitive, followed by "around") To attempt to obtain information by talking to people.
    The detective visited the local pubs fishing around for more information.
  5. (intransitive, cricket) Of a batsman, to attempt to hit a ball outside off stump and miss it.
  6. (transitive, followed by "for") To attempt to get hold of (an object) that is among other objects.
  7. (transitive, figuratively, followed by "for") To attempt to gain.
    The actors loitered at the door, fishing for compliments.
  8. (nautical) To repair a spar or mast using a brace often called a fish (see NOUN above).
    1970 Henderson, James, The Frigates, an account of the lesser warships of the wars from 1793 to 1815; Wordsworth edition of 1998, p143:
    • [...] the crew were set to replacing and splicing the rigging and fishing the spars.
  • (try to catch a fish): angle, drop in a line
  • (try to find something): rifle, rummage
  • (attempt to get hold of (an object) among others): rummage
  • (attempt to gain (compliments, etc)): angle
Derived terms

External links

Bible wiki

Up to date as of January 23, 2010

From BibleWiki

called dag by the Hebrews, a word denoting great fecundity (Gen 9:2; Num 11:22; Jonah 2:1, Jonah 2:10). No fish is mentioned by name either in the Old or in the New Testament. Fish abounded in the Mediterranean and in the lakes of the Jordan, so that the Hebrews were no doubt acquainted with many species. Two of the villages on the shores of the Sea of Galilee derived their names from their fisheries, Bethsaida (the "house of fish") on the east and on the west. There is probably no other sheet of water in the world of equal dimensions that contains such a variety and profusion of fish. About thirty-seven different kinds have been found. Some of the fishes are of a European type, such as the roach, the barbel, and the blenny; others are markedly African and tropical, such as the eel-like silurus. There was a regular fish-market apparently in Jerusalem (2Chr 33:14; Neh 3:3; Neh 12:39; Zeph 1:10), as there was a fish-gate which was probably contiguous to it.

Sidon is the oldest fishing establishment known in history.

This entry includes text from Easton's Bible Dictionary, 1897.

what mentions this? (please help by turning references to this page into wiki links)

Simple English

[[File:|thumb|200px|Fish come in many shapes and sizes. This is a sea dragon, a close relative of the seahorse. They are camouflaged as floating seaweed.[1][2]]]

File:Dunkleosteus skull QM
Duncklosteus, a giant armoured arthrodire of the late Devonian. Inland seas of North America, up to 6 metres long.[3]

A fish (plural: fish or fishes) is a class of vertebrates that live in water. They are covered with scales, and have two sets of paired fins, and several unpaired fins. They are usually cold-blooded. A fish takes in the oxygen from the water using gills. There are many different kinds of fish. They live in fresh water in lakes and rivers, and in salt water in the ocean. Some fish are less than one centimeter long. The largest fish is the whale shark, which can be almost 15 meters long and weigh 15 tons.

Certain animals that have the word fish in their name are not really fish: Crayfish are crustaceans, and jellyfish are Cnidarians.


Types of fish

Fish, the oldest vertebrate group, includes a huge range of types, from the Middle Ordovician, about 490 million years ago, to the present day. These are the main groups:[4][5][6]

  • Agnatha: the jawless fish
    • Pteraspids: the head-shields
    • Anaspids: gills opened as holes. Silurian to end-Devonian.
      • Cephalaspids: early jawless fish
      • Lampreys: living ectoparasites
    • Osteostraci: bony-armoured jawless fish.


File:Lampanyctodes hectoris (Hector's lanternfish)
The anatomy of Lampanyctodes hectoris
1. operculum (gill cover) 2 & 5. lateral line 3. dorsal fin 4 fat fin 6. caudal fin 7. anal fin 8. photophores 9. pelvic fins paired 10. pectoral fins (paired)

Bony and cartilagenous fish

Most kinds of fish have bones. Some kinds of fish, such as sharks and rays, do not have real bones (their skeletons are made of cartilage) they are known as cartilagenous fish.

Fish scales

All fish are covered with overlapping scales, and each major group of fish has its own special type of scale. Teleosts ('modern' fish) have what are called leptoid scales. These grow in concentric circles and overlap in a head to tail direction like roof tiles. Sharks and other chondrichthyes have placoid scales made of denticles, like small versions of their teeth. These also overlap in a head to tail direction, producing a tough outer layer. Shark skin is available for purchase as shagreen, a leather which as original is smooth in one direction, and rough in the other direction. It may be polished for use, but is always rough in texture and resistant to slipping.

The scales are usually covered with a layer of slime which improves passage through the water, and makes the fish more slippery to a predator.


Fish swim by exerting force against the surrounding water. There are exceptions, but this is usually done by the fish contracting muscles on either side of its body in order to generate waves of flexion that travel the length of the body from nose to tail, generally getting larger as they go along. Most fishes generate thrust using lateral movements of their body & tail fin (caudal fin). However, there are also species which move mainly using their median and paired fins. The latter group profits from the gained manoeuvrability that is needed when living in coral reefs for example. But they can not swim as fast as fish using their bodies & caudal fins.[7]

The fusiform shape of this shark makes it an efficient swimmer. It is fast over short distances.

The shape of the body of a fish is important to its swimming. This is because streamlined body shapes makes the water drag less. Here are some common fish shapes.


The picture on the left shows a shark. This shark's shape is called fusiform, and it is an ovoid shape where both ends of the fish are pointy. This is the best shape for going through water quickly.[8][9] Fishes with fusiform shapes can chase prey and escape predators quickly. Many live in the open ocean and swim constantly, like marlins, swordfish, and tuna. Ichthyosaurs, porpoises, dolphins, killer whales all have similar shapes. This is an example of convergent evolution.


The long, ribbon-like shape of an eel's body shows another shape. This enables them to hide in cracks, springing out quickly to capture prey, then returning quickly to their hiding spot.


A flounder has both of its eyes on one side of its body.

Flatfish live on the bottom of the ocean or lake. Most use camouflage: they change colors to match the ocean floor.


Fish with compressed shapes have flat, vertical bodies, with one eye on each side. They swim upright and can be very thin. They usually live in reefs where their flat bodies can slip in and out among the corals, sponges, and rocks, keeping hidden from predators. Angelfish, surgeonfish, and butterflyfish are all compressed fish.

Fish as food

People eat many kinds of fish. The fish that people eat most include carp, cod, herring, perch, sardines, sturgeon, tilapia, trout, tuna, and many others. Some people keep fish as pets. Goldfish and Siamese Fighting Fish are popular types of pet fish. They are often kept by groups of people in public ponds for their beauty and calming nature.


See also: Fishing
The word to fish is also used for the activity of catching fish. People catch fish with small nets from the side of the water or from small boats, or with big nets from big boats. People can also catch fish with fishing poles and fishhooks with bait. This is often called fishing. There is also different types of lures that can be used. One is a crank bait. Others are plastic worms and rat-l-traps. These are lots of different ways of catching fish.


  1. Leafy and Weedy Sea Dragon National Geographic Profile. Retrieved 20 July 2009.
  2. Connolly R (2006). Phycodurus eques. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 20 July 2009.
  3. Long J.A. 1995. The rise of fishes: 500 million years of evolution. Johns Hopkins, Baltimore.
  4. Helfman G. Collette B. & Facey D. 1997. The diversity of fishes: biology, evolution and ecology. Blackwell, Oxford.
  5. Moyle P.B. and Cech J.J. 2003. Fishes: an introduction to Ichthyology. 5th ed, Cummings. ISBN 978-0-13-100847-2
  6. Maisey J.G. 1996. Discovering fossil fishes. Holt N.Y.
  7. Breder C.M. 2003. The locomotion of fishes. Zoologica, 4, 159-256, (1926); Journal of Experimental Biology 206, 2749-2758 (2003)
  8. Nielsen, Knut Schmidt 1984. Scaling: why is animal size so important? Cambridge. Chapter 15
  9. Baily, Jill 1997. How fish swim. Benchmark, N.Y.
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