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For fish as eaten by humans, see Fish as food. Fish_sentence_0

For other uses, see Fish (disambiguation). Fish_sentence_1


FishTemporal range: Mid Cambrian–Recent

PreꞒ O S D C P T J K Pg NFish_header_cell_0_0_0

Scientific classificationVertebrataFish_header_cell_0_1_0
Kingdom:Fish_cell_0_2_0 AnimaliaFish_cell_0_2_1
Phylum:Fish_cell_0_3_0 ChordataFish_cell_0_3_1
Clade:Fish_cell_0_4_0 OlfactoresFish_cell_0_4_1
Subphylum:Fish_cell_0_5_0 VertebrataFish_cell_0_5_1
Groups includedFish_header_cell_0_6_0
Cladistically included but traditionally excluded taxaFish_header_cell_0_7_0

Fish are gill-bearing aquatic craniate animals that lack limbs with digits. Fish_sentence_2

They form a sister group to the tunicates, together forming the olfactores. Fish_sentence_3

Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Fish_sentence_4

Around 99% of living fish species are ray-finned fish, belonging to the class Actinopterygii, with over 95% belonging to the teleost subgrouping. Fish_sentence_5

The earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period. Fish_sentence_6

Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts. Fish_sentence_7

Fish would continue to evolve through the Paleozoic era, diversifying into a wide variety of forms. Fish_sentence_8

Many fish of the Paleozoic developed external armor that protected them from predators. Fish_sentence_9

The first fish with jaws appeared in the Silurian period, after which many (such as sharks) became formidable marine predators rather than just the prey of arthropods. Fish_sentence_10

Most fish are ectothermic ("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like white shark and tuna can hold a higher core temperature. Fish_sentence_11

Fish can communicate in their underwater environments through the use of acoustic communication. Fish_sentence_12

Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another. Fish_sentence_13

The production of sounds as a means of communication among fish is most often used in the context of feeding, aggression or courtship behaviour. Fish_sentence_14

The sounds emitted by fish can vary depending on the species and stimulus involved. Fish_sentence_15

They can produce either stridulatory sounds by moving components of the skeletal system, or can produce non-stridulatory sounds by manipulating specialized organs such as the swimbladder. Fish_sentence_16

Fish are abundant in most bodies of water. Fish_sentence_17

They can be found in nearly all aquatic environments, from high mountain streams (e.g., char and gudgeon) to the abyssal and even hadal depths of the deepest oceans (e.g., cusk-eels and snailfish), although no species has yet been documented in the deepest 25% of the ocean. Fish_sentence_18

With 34,300 described species, fish exhibit greater species diversity than any other group of vertebrates. Fish_sentence_19

Fish are an important resource for humans worldwide, especially as food. Fish_sentence_20

Commercial and subsistence fishers hunt fish in wild fisheries or farm them in ponds or in cages in the ocean (in aquaculture). Fish_sentence_21

They are also caught by recreational fishers, kept as pets, raised by fishkeepers, and exhibited in public aquaria. Fish_sentence_22

Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies. Fish_sentence_23

Tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. Fish_sentence_24

However, traditionally fish are rendered paraphyletic by excluding the tetrapods (i.e., the amphibians, reptiles, birds and mammals which all descended from within the same ancestry). Fish_sentence_25

Because in this manner the term "fish" is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology, unless it is used in the cladistic sense, including tetrapods. Fish_sentence_26

The traditional term pisces (also ichthyes) is considered a , but not a phylogenetic classification. Fish_sentence_27

Etymology Fish_section_0

The word for fish in English and the other Germanic languages (German fisch; Gothic fisks) is inherited from Proto-Germanic, and is related to the Latin piscis and Old Irish īasc, though the exact root is unknown; some authorities reconstruct an Proto-Indo-European root *peysk-, attested only in Italic, Celtic, and Germanic. Fish_sentence_28

The English word once had a much broader usage than its current biological meaning. Fish_sentence_29

Names such as starfish, jellyfish, shellfish and cuttlefish attest to most any fully aquatic animal (including whales) once being 'fish'. Fish_sentence_30

"Correcting" such names (e.g. to 'sea star') is an attempt to retroactively apply the current meaning of 'fish' to words that were coined when it had a different meaning. Fish_sentence_31

Evolution Fish_section_1

Main article: Evolution of fish Fish_sentence_32

Fish, as vertebrata, developed as sister of the tunicata. Fish_sentence_33

As the tetrapods emerged deep within the fishes group, as sister of the lungfish, characteristics of fish are typically shared by tetrapods, including having vertebrae and a cranium. Fish_sentence_34

Early fish from the fossil record are represented by a group of small, jawless, armored fish known as ostracoderms. Fish_sentence_35

Jawless fish lineages are mostly extinct. Fish_sentence_36

An extant clade, the lampreys may approximate ancient pre-jawed fish. Fish_sentence_37

The first jaws are found in Placodermi fossils. Fish_sentence_38

They lacked distinct teeth, having instead the oral surfaces of their jaw plates modified to serve the various purposes of teeth. Fish_sentence_39

The diversity of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth. Fish_sentence_40

It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination of factors. Fish_sentence_41

Fish may have evolved from a creature similar to a coral-like sea squirt, whose larvae resemble primitive fish in important ways. Fish_sentence_42

The first ancestors of fish may have kept the larval form into adulthood (as some sea squirts do today), although perhaps the reverse is the case. Fish_sentence_43

Taxonomy Fish_section_2

Fish are a paraphyletic group: that is, any clade containing all fish also contains the tetrapods, which are not fish. Fish_sentence_44

For this reason, groups such as the class Pisces seen in older reference works are no longer used in formal classifications. Fish_sentence_45

Traditional classification divides fish into three extant classes, and with extinct forms sometimes classified within the tree, sometimes as their own classes: Fish_sentence_46


The above scheme is the one most commonly encountered in non-specialist and general works. Fish_sentence_47

Many of the above groups are paraphyletic, in that they have given rise to successive groups: Agnathans are ancestral to Chondrichthyes, who again have given rise to Acanthodiians, the ancestors of Osteichthyes. Fish_sentence_48

With the arrival of phylogenetic nomenclature, the fishes has been split up into a more detailed scheme, with the following major groups: Fish_sentence_49


† – indicates extinct taxon Some palaeontologists contend that because Conodonta are chordates, they are primitive fish. Fish_sentence_50

For a fuller treatment of this taxonomy, see the vertebrate article. Fish_sentence_51

The position of hagfish in the phylum Chordata is not settled. Fish_sentence_52

Phylogenetic research in 1998 and 1999 supported the idea that the hagfish and the lampreys form a natural group, the Cyclostomata, that is a sister group of the Gnathostomata. Fish_sentence_53

The various fish groups account for more than half of vertebrate species. Fish_sentence_54

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 hagfish and lampreys. Fish_sentence_55

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. Fish_sentence_56

About 64 families are monotypic, containing only one species. Fish_sentence_57

The final total of extant species may grow to exceed 32,500. Fish_sentence_58

Diversity Fish_section_3

Main article: Diversity of fish Fish_sentence_59


  • Fish_item_2_37
  • Fish_item_2_38
  • Fish_item_2_39
  • Fish_item_2_40

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. Fish_sentence_60

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 fish, coelacanths, and lungfish. Fish_sentence_61

Indeed, lungfish and coelacanths are closer relatives of tetrapods (such as mammals, birds, amphibians, etc.) than of other fish such as ray-finned fish or sharks, so the last common ancestor of all fish is also an ancestor to tetrapods. Fish_sentence_62

As paraphyletic groups are no longer recognised in modern systematic biology, the use of the term "fish" as a biological group must be avoided. Fish_sentence_63

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. Fish_sentence_64

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. Fish_sentence_65

However, according to the definition above, all mammals, including cetaceans like whales and dolphins, are not fish. Fish_sentence_66

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_sentence_67

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. Fish_sentence_68

Each criterion has exceptions. Fish_sentence_69

Tuna, swordfish, and some species of sharks show some warm-blooded adaptations – they can heat their bodies significantly above ambient water temperature. Fish_sentence_70

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. Fish_sentence_71

Many groups of freshwater fish extract oxygen from the air as well as from the water using a variety of different structures. Fish_sentence_72

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. Fish_sentence_73

Body shape and the arrangement of the fins is highly variable, covering such seemingly un-fishlike forms as seahorses, pufferfish, anglerfish, and gulpers. Fish_sentence_74

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 lungfish and coelacanths), ganoid (various fossil fish but also living gars and bichirs), cycloid, and ctenoid (these last two are found on most bony fish). Fish_sentence_75

There are even fish that live mostly on land or lay their eggs on land near water. Fish_sentence_76

Mudskippers feed and interact with one another on mudflats and go underwater to hide in their burrows. Fish_sentence_77

A single, undescribed species of Phreatobius, has been called a true "land fish" as this worm-like catfish strictly lives among waterlogged leaf litter. Fish_sentence_78

Many species live in underground lakes, underground rivers or aquifers and are popularly known as cavefish. Fish_sentence_79

Fish range in size from the huge 16-metre (52 ft) whale shark to the tiny 8-millimetre (0.3 in) stout infantfish. Fish_sentence_80

Fish species diversity is roughly divided equally between marine (oceanic) and freshwater ecosystems. Fish_sentence_81

Coral reefs in the Indo-Pacific constitute the center of diversity for marine fishes, whereas continental freshwater fishes are most diverse in large river basins of tropical rainforests, especially the Amazon, Congo, and Mekong basins. Fish_sentence_82

More than 5,600 fish species inhabit Neotropical freshwaters alone, such that Neotropical fishes represent about 10% of all vertebrate species on the Earth. Fish_sentence_83

Exceptionally rich sites in the Amazon basin, such as Cantão State Park, can contain more freshwater fish species than occur in all of Europe. Fish_sentence_84

The deepest living fish in the ocean so far found is the Mariana snailfish (Pseudoliparis swirei) which lives at deeps of 8,000 meters (26,200 feet) along the Mariana Trench near Guam. Fish_sentence_85

Anatomy and physiology Fish_section_4

Further information: Fish anatomy and Fish physiology Fish_sentence_86

Respiration Fish_section_5

See also: Aquatic respiration Fish_sentence_87

Gills Fish_section_6

Most fish exchange gases using gills on either side of the pharynx. Fish_sentence_88

Gills consist of threadlike structures called filaments. Fish_sentence_89

Each filament contains a capillary network that provides a large surface area for exchanging oxygen and carbon dioxide. Fish_sentence_90

Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills. Fish_sentence_91

In some fish, capillary blood flows in the opposite direction to the water, causing countercurrent exchange. Fish_sentence_92

The gills push the oxygen-poor water out through openings in the sides of the pharynx. Fish_sentence_93

Some fish, like sharks and lampreys, possess multiple gill openings. Fish_sentence_94

However, bony fish have a single gill opening on each side. Fish_sentence_95

This opening is hidden beneath a protective bony cover called an operculum. Fish_sentence_96

Juvenile bichirs have external gills, a very primitive feature that they share with larval amphibians. Fish_sentence_97

Air breathing Fish_section_7

Fish from multiple groups can live out of the water for extended periods. Fish_sentence_98

Amphibious fish such as the mudskipper can live and move about on land for up to several days, or live in stagnant or otherwise oxygen depleted water. Fish_sentence_99

Many such fish can breathe air via a variety of mechanisms. Fish_sentence_100

The skin of anguillid eels may absorb oxygen directly. Fish_sentence_101

The buccal cavity of the electric eel may breathe air. Fish_sentence_102

Catfish of the families Loricariidae, Callichthyidae, and Scoloplacidae absorb air through their digestive tracts. Fish_sentence_103

Lungfish, with the exception of the Australian 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. Fish_sentence_104

Gar and bowfin have a vascularized swim bladder that functions in the same way. Fish_sentence_105

Loaches, trahiras, and many catfish breathe by passing air through the gut. Fish_sentence_106

Mudskippers breathe by absorbing oxygen across the skin (similar to frogs). Fish_sentence_107

A number of fish have evolved so-called accessory breathing organs that extract oxygen from the air. Fish_sentence_108

Labyrinth fish (such as gouramis and bettas) have a labyrinth organ above the gills that performs this function. Fish_sentence_109

A few other fish have structures resembling labyrinth organs in form and function, most notably snakeheads, pikeheads, and the Clariidae catfish family. Fish_sentence_110

Breathing air is primarily of use to fish that inhabit shallow, seasonally variable waters where the water's oxygen concentration may seasonally decline. Fish_sentence_111

Fish 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. Fish_sentence_112

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. Fish_sentence_113

Air breathing fish can be divided into obligate air breathers and facultative air breathers. Fish_sentence_114

Obligate air breathers, such as the African lungfish, must breathe air periodically or they suffocate. Fish_sentence_115

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. Fish_sentence_116

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. Fish_sentence_117

Circulation Fish_section_8

Fish have a closed-loop circulatory system. Fish_sentence_118

The heart pumps the blood in a single loop throughout the body. Fish_sentence_119

In most fish, the heart consists of four parts, including two chambers and an entrance and exit. Fish_sentence_120

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. Fish_sentence_121

The atrium serves as a one-way antechamber, sends blood to the third part, ventricle. Fish_sentence_122

The ventricle is another thick-walled, muscular chamber and it pumps the blood, first to the fourth part, bulbus arteriosus, a large tube, and then out of the heart. Fish_sentence_123

The bulbus arteriosus connects to the aorta, through which blood flows to the gills for oxygenation. Fish_sentence_124

Digestion Fish_section_9

Jaws allow fish to eat a wide variety of food, including plants and other organisms. Fish_sentence_125

Fish ingest food through the mouth and break it down in the esophagus. Fish_sentence_126

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. Fish_sentence_127

Organs such as the liver and pancreas add enzymes and various chemicals as the food moves through the digestive tract. Fish_sentence_128

The intestine completes the process of digestion and nutrient absorption. Fish_sentence_129

Excretion Fish_section_10

As with many aquatic animals, most fish release their nitrogenous wastes as ammonia. Fish_sentence_130

Some of the wastes diffuse through the gills. Fish_sentence_131

Blood wastes are filtered by the kidneys. Fish_sentence_132

Saltwater fish tend to lose water because of osmosis. Fish_sentence_133

Their kidneys return water to the body. Fish_sentence_134

The reverse happens in freshwater fish: they tend to gain water osmotically. Fish_sentence_135

Their kidneys produce dilute urine for excretion. Fish_sentence_136

Some fish have specially adapted kidneys that vary in function, allowing them to move from freshwater to saltwater. Fish_sentence_137

Scales Fish_section_11

Main article: Fish scale Fish_sentence_138

The scales of fish originate from the mesoderm (skin); they may be similar in structure to teeth. Fish_sentence_139

Sensory and nervous system Fish_section_12

Central nervous system Fish_section_13

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. Fish_sentence_140

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. Fish_sentence_141

Fish brains are divided into several regions. Fish_sentence_142

At the front are the olfactory lobes, a pair of structures that receive and process signals from the nostrils via the two olfactory nerves. Fish_sentence_143

The olfactory lobes are very large in fish that hunt primarily by smell, such as hagfish, sharks, and catfish. Fish_sentence_144

Behind the olfactory lobes is the two-lobed telencephalon, the structural equivalent to the cerebrum in higher vertebrates. Fish_sentence_145

In fish the telencephalon is concerned mostly with olfaction. Fish_sentence_146

Together these structures form the forebrain. Fish_sentence_147

Connecting the forebrain to the midbrain is the diencephalon (in the diagram, this structure is below the optic lobes and consequently not visible). Fish_sentence_148

The diencephalon performs functions associated with hormones and homeostasis. Fish_sentence_149

The pineal body lies just above the diencephalon. Fish_sentence_150

This structure detects light, maintains circadian rhythms, and controls color changes. Fish_sentence_151

The midbrain (or mesencephalon) contains the two optic lobes. Fish_sentence_152

These are very large in species that hunt by sight, such as rainbow trout and cichlids. Fish_sentence_153

The hindbrain (or metencephalon) is particularly involved in swimming and balance. Fish_sentence_154

The cerebellum is a single-lobed structure that is typically the biggest part of the brain. Fish_sentence_155

Hagfish and lampreys have relatively small cerebellae, while the mormyrid cerebellum is massive and apparently involved in their electrical sense. Fish_sentence_156

The brain stem (or myelencephalon) is the brain's posterior. Fish_sentence_157

As well as controlling some muscles and body organs, in bony fish at least, the brain stem governs respiration and osmoregulation. Fish_sentence_158

Sense organs Fish_section_14

Most fish possess highly developed sense organs. Fish_sentence_159

Nearly all daylight fish have color vision that is at least as good as a human's (see vision in fishes). Fish_sentence_160

Many fish also have chemoreceptors that are responsible for extraordinary senses of taste and smell. Fish_sentence_161

Although they have ears, many fish may not hear very well. Fish_sentence_162

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. Fish_sentence_163

Some fish, such as catfish and sharks, have the ampullae of Lorenzini, electroreceptors that detect weak electric currents on the order of millivolt. Fish_sentence_164

Other fish, like the South American electric fishes Gymnotiformes, can produce weak electric currents, which they use in navigation and social communication. Fish_sentence_165

Fish orient themselves using landmarks and may use mental maps based on multiple landmarks or symbols. Fish_sentence_166

Fish behavior in mazes reveals that they possess spatial memory and visual discrimination. Fish_sentence_167

Vision Fish_section_15

Main article: Vision in fishes Fish_sentence_168

Vision is an important sensory system for most species of fish. Fish_sentence_169

Fish eyes are similar to those of terrestrial vertebrates like birds and mammals, but have a more spherical lens. Fish_sentence_170

Their retinas generally have both rods and cones (for scotopic and photopic vision), and most species have colour vision. Fish_sentence_171

Some fish can see ultraviolet and some can see polarized light. Fish_sentence_172

Amongst jawless fish, the lamprey has well-developed eyes, while the hagfish has only primitive eyespots. Fish_sentence_173

Fish vision shows adaptation to their visual environment, for example deep sea fishes have eyes suited to the dark environment. Fish_sentence_174

Hearing Fish_section_16

See also: Sensory systems in fish § Hearing Fish_sentence_175

Hearing is an important sensory system for most species of fish. Fish_sentence_176

Fish sense sound using their lateral lines and their ears. Fish_sentence_177

Cognition Fish_section_17

Further information: Fish intelligence Fish_sentence_178

New research has expanded preconceptions about the cognitive capacities of fish. Fish_sentence_179

For example, manta rays have exhibited behavior linked to self-awareness in mirror test cases. Fish_sentence_180

Placed in front of a mirror, individual rays engaged in contingency testing, that is, repetitive behavior aiming to check whether their reflection's behavior mimics their body movement. Fish_sentence_181

Wrasses have also passed the mirror test in a 2018 scientific study. Fish_sentence_182

Cases of tool use have also been noticed, notably in the Choerodon family, in archerfish and Atlantic cod. Fish_sentence_183

Capacity for pain Fish_section_18

Further information: Pain in fish Fish_sentence_184

Experiments done by William Tavolga provide evidence that fish have pain and fear responses. Fish_sentence_185

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. Fish_sentence_186

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. Fish_sentence_187

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. Fish_sentence_188

Neurons fired in a pattern resembling human neuronal patterns. Fish_sentence_189

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". Fish_sentence_190

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. Fish_sentence_191

Rose had published a study a year earlier arguing that fish cannot feel pain because their brains lack a neocortex. Fish_sentence_192

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." Fish_sentence_193

Animal welfare advocates raise concerns about the possible suffering of fish caused by angling. Fish_sentence_194

Some countries, such as Germany have banned specific types of fishing, and the British RSPCA now formally prosecutes individuals who are cruel to fish. Fish_sentence_195

Emotion Fish_section_19

In 2019, scientists have shown that members of the monogamous species Amatitlania siquia exhibit pessimistic behavior when they are prevented from being with their partner. Fish_sentence_196

Muscular system Fish_section_20

Main article: Fish locomotion Fish_sentence_197

Most fish move by alternately contracting paired sets of muscles on either side of the backbone. Fish_sentence_198

These contractions form S-shaped curves that move down the body. Fish_sentence_199

As each curve reaches the back fin, backward force is applied to the water, and in conjunction with the fins, moves the fish forward. Fish_sentence_200

The fish's fins function like an airplane's flaps. Fish_sentence_201

Fins also increase the tail's surface area, increasing speed. Fish_sentence_202

The streamlined body of the fish decreases the amount of friction from the water. Fish_sentence_203

Since body tissue is denser than water, fish must compensate for the difference or they will sink. Fish_sentence_204

Many bony fish have an internal organ called a swim bladder that adjusts their buoyancy through manipulation of gases. Fish_sentence_205

Endothermy Fish_section_21

Although most fish are exclusively ectothermic, there are exceptions. Fish_sentence_206

The only known bony fishes (infraclass Teleostei) that exhibit endothermy are in the suborder Scombroidei – which includes the billfishes, tunas, and the butterfly kingfish, a basal species of mackerel – and also the opah. Fish_sentence_207

The opah, a lampriform, was demonstrated in 2015 to utilize "whole-body endothermy", generating heat with its swimming muscles to warm its body while countercurrent exchange (as in respiration) minimizes heat loss. Fish_sentence_208

It is able to actively hunt prey such as squid and swim for long distances due to the ability to warm its entire body, including its heart, which is a trait typically found in only mammals and birds (in the form of homeothermy). Fish_sentence_209

In the cartilaginous fishes (class Chondrichthyes), sharks of the families Lamnidae (porbeagle, mackerel, salmon, and great white sharks) and Alopiidae (thresher sharks) exhibit endothermy. Fish_sentence_210

The degree of endothermy varies from the billfishes, which warm only their eyes and brain, to the bluefin tuna and the porbeagle shark, which maintain body temperatures in excess of 20 °C (68 °F) above ambient water temperatures. Fish_sentence_211

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. Fish_sentence_212

Reproductive system Fish_section_22

Further information: Fish reproduction and Spawn (biology) Fish_sentence_213

Fish reproductive organs include testicles and ovaries. Fish_sentence_214

In most species, gonads are paired organs of similar size, which can be partially or totally fused. Fish_sentence_215

There may also be a range of secondary organs that increase reproductive fitness. Fish_sentence_216

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 fish they are confined to the distal portion of these structures. Fish_sentence_217

Fish can present cystic or semi-cystic spermatogenesis in relation to the release phase of germ cells in cysts to the seminiferous tubules lumen. Fish_sentence_218

Fish ovaries may be of three types: gymnovarian, secondary gymnovarian or cystovarian. Fish_sentence_219

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. Fish_sentence_220

Secondary gymnovarian ovaries shed ova into the coelom from which they go directly into the oviduct. Fish_sentence_221

In the third type, the oocytes are conveyed to the exterior through the oviduct. Fish_sentence_222

Gymnovaries are the primitive condition found in lungfish, sturgeon, and bowfin. Fish_sentence_223

Cystovaries characterize most teleosts, where the ovary lumen has continuity with the oviduct. Fish_sentence_224

Secondary gymnovaries are found in salmonids and a few other teleosts. Fish_sentence_225

Oogonia development in teleosts fish varies according to the group, and the determination of oogenesis dynamics allows the understanding of maturation and fertilization processes. Fish_sentence_226

Changes in the nucleus, ooplasm, and the surrounding layers characterize the oocyte maturation process. Fish_sentence_227

Postovulatory follicles are structures formed after oocyte release; they do not have endocrine function, present a wide irregular lumen, and are rapidly reabsorbed in a process involving the apoptosis of follicular cells. Fish_sentence_228

A degenerative process called follicular atresia reabsorbs vitellogenic oocytes not spawned. Fish_sentence_229

This process can also occur, but less frequently, in oocytes in other development stages. Fish_sentence_230

Some fish, like the California sheephead, are hermaphrodites, having both testes and ovaries either at different phases in their life cycle or, as in hamlets, have them simultaneously. Fish_sentence_231

Over 97% of all known fish are oviparous, that is, the eggs develop outside the mother's body. Fish_sentence_232

Examples of oviparous fish include salmon, goldfish, cichlids, tuna, and eels. Fish_sentence_233

In the majority of these species, fertilisation takes place outside the mother's body, with the male and female fish shedding their gametes into the surrounding water. Fish_sentence_234

However, a few oviparous fish 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. Fish_sentence_235

In these cases, the male is equipped with a pair of modified pelvic fins known as claspers. Fish_sentence_236

Marine fish can produce high numbers of eggs which are often released into the open water column. Fish_sentence_237

The eggs have an average diameter of 1 millimetre (0.04 in). Fish_sentence_238


  • Fish_item_3_41
  • Fish_item_3_42
  • Fish_item_3_43
  • Fish_item_3_44

The newly hatched young of oviparous fish are called larvae. Fish_sentence_239

They are usually poorly formed, carry a large yolk sac (for nourishment), and are very different in appearance from juvenile and adult specimens. Fish_sentence_240

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. Fish_sentence_241

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. Fish_sentence_242

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. Fish_sentence_243

Each embryo develops in its own egg. Fish_sentence_244

Familiar examples of ovoviviparous fish include guppies, angel sharks, and coelacanths. Fish_sentence_245

Some species of fish are viviparous. Fish_sentence_246

In such species the mother retains the eggs and nourishes the embryos. Fish_sentence_247

Typically, viviparous fish have a structure analogous to the placenta seen in mammals connecting the mother's blood supply with that of the embryo. Fish_sentence_248

Examples of viviparous fish include the surf-perches, splitfins, and lemon shark. Fish_sentence_249

Some viviparous fish exhibit oophagy, in which the developing embryos eat other eggs produced by the mother. Fish_sentence_250

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. Fish_sentence_251

Intrauterine cannibalism is an even more unusual mode of vivipary, in which the largest embryos eat weaker and smaller siblings. Fish_sentence_252

This behavior is also most commonly found among sharks, such as the grey nurse shark, but has also been reported for Nomorhamphus ebrardtii. Fish_sentence_253

Aquarists commonly refer to ovoviviparous and viviparous fish as livebearers. Fish_sentence_254

Acoustic communication in fish Fish_section_23

Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another. Fish_sentence_255

The production of sounds as a means of communication among fish is most often used in the context of feeding, aggression or courtship behaviour. Fish_sentence_256

The sounds emitted can vary depending on the species and stimulus involved. Fish_sentence_257

Fish can produce either stridulatory sounds by moving components of the skeletal system, or can produce non-stridulatory sounds by manipulating specialized organs such as the swimbladder. Fish_sentence_258

Stridulatory sound producing mechanisms Fish_section_24

There are some species of fish that can produce sounds by rubbing or grinding their bones together. Fish_sentence_259

These noises produced by bone-on-bone interactions are known as 'stridulatory sounds'. Fish_sentence_260

An example of this is seen in Haemulon flavolineatum, a species commonly referred to as the 'French grunt fish', as it produces a grunting noise by grinding its teeth together. Fish_sentence_261

This behaviour is most pronounced when the H. Fish_sentence_262 flavolineatum is in distress situations. Fish_sentence_263

The grunts produced by this species of fishes generate a frequency of approximately 700 Hz, and last approximately 47 milliseconds. Fish_sentence_264

The H. Fish_sentence_265 flavolineatum does not emit sounds with frequencies greater than 1000 Hz, and does not detect sounds that have frequencies greater than 1050 Hz. Fish_sentence_266

In a study conducted by Oliveira et al. Fish_sentence_267

(2014), the longsnout seahorse, Hippocampus reidi, was recorded producing two different categories of sounds; ‘clicks’ and ‘growls’. Fish_sentence_268

The sounds emitted by the H. Fish_sentence_269 reidi are accomplished by rubbing their coronet bone across the grooved section of their neurocranium. Fish_sentence_270

‘Clicking’ sounds were found to be primarily produced during courtship and feeding, and the frequencies of clicks were within the range of 50 Hz-800 Hz. Fish_sentence_271

The frequencies were noted to be on the higher end of the range during spawning periods, when the female and male fishes were less than fifteen centimeters apart. Fish_sentence_272

Growl sounds were produced when the H. Fish_sentence_273 reidi encountered stressful situations, such as handling by researchers. Fish_sentence_274

The 'growl' sounds consist of a series of sound pulses and are emitted simultaneously with body vibrations. Fish_sentence_275

Non-stridulatory sound producing mechanisms Fish_section_25

Some fish species create noise by engaging specialized muscles that contract and cause swimbladder vibrations. Fish_sentence_276

Oyster toadfish produce loud grunting sounds by contracting muscles located along the sides of their swim bladder, known as sonic muscles Female and male toadfishes emit short-duration grunts, often as a fright response. Fish_sentence_277

In addition to short-duration grunts, male toadfishes produce “boat whistle calls”. Fish_sentence_278

These calls are longer in duration, lower in frequency, and are primarily used to attract mates. Fish_sentence_279

The sounds emitted by the O. tao have frequency range of 140 Hz to 260 Hz. Fish_sentence_280

The frequencies of the calls depend on the rate at which the sonic muscles contract. Fish_sentence_281

The red drum, Sciaenops ocellatus, produces drumming sounds by vibrating its swimbladder. Fish_sentence_282

Vibrations are caused by the rapid contraction of sonic muscles that surround the dorsal aspect of the swimbladder. Fish_sentence_283

These vibrations result in repeated sounds with frequencies that range from 100 to >200 Hz. Fish_sentence_284

The S. Fish_sentence_285 Ocellatus can produce different calls depending on the stimuli involved. Fish_sentence_286

The sounds created in courtship situations are different from those made during distressing events such as predatorial attacks. Fish_sentence_287

Unlike the males of the S. Fish_sentence_288 Ocellatus species, the females of this species don't produce sounds and lack sound-producing (sonic) muscles. Fish_sentence_289

Diseases Fish_section_26

Main article: Fish diseases and parasites Fish_sentence_290

Like other animals, fish suffer from diseases and parasites. Fish_sentence_291

To prevent disease they have a variety of defenses. Fish_sentence_292

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. Fish_sentence_293

If 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. Fish_sentence_294

Specific defenses respond to particular pathogens recognised by the fish's body, i.e., an immune response. Fish_sentence_295

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. Fish_sentence_296

Some species use cleaner fish to remove external parasites. Fish_sentence_297

The best known of these are the Bluestreak cleaner wrasses of the genus Labroides found on coral reefs in the Indian and Pacific oceans. Fish_sentence_298

These small fish maintain so-called "cleaning stations" where other fish congregate and perform specific movements to attract the attention of the cleaners. Fish_sentence_299

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. Fish_sentence_300

Immune system Fish_section_27

Immune organs vary by type of fish. Fish_sentence_301

In the jawless fish (lampreys and hagfish), true lymphoid organs are absent. Fish_sentence_302

These fish rely on regions of lymphoid tissue within other organs to produce immune cells. Fish_sentence_303

For example, erythrocytes, macrophages and plasma cells are produced in the anterior kidney (or pronephros) and some areas of the gut (where granulocytes mature.) Fish_sentence_304

They resemble primitive bone marrow in hagfish. Fish_sentence_305

Cartilaginous fish (sharks and rays) have a more advanced immune system. Fish_sentence_306

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. Fish_sentence_307

These organs house typical immune cells (granulocytes, lymphocytes and plasma cells). Fish_sentence_308

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. Fish_sentence_309

Chondrostean fish (sturgeons, paddlefish, and bichirs) possess a major site for the production of granulocytes within a mass that is associated with the meninges (membranes surrounding the central nervous system.) Fish_sentence_310

Their heart is frequently covered with tissue that contains lymphocytes, reticular cells and a small number of macrophages. Fish_sentence_311

The chondrostean kidney is an important hemopoietic organ; where erythrocytes, granulocytes, lymphocytes and macrophages develop. Fish_sentence_312

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. Fish_sentence_313

In addition, teleost fish possess a thymus, spleen and scattered immune areas within mucosal tissues (e.g. in the skin, gills, gut and gonads). Fish_sentence_314

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. Fish_sentence_315

In 2006, a lymphatic system similar to that in mammals was described in one species of teleost fish, the zebrafish. Fish_sentence_316

Although not confirmed as yet, this system presumably will be where naive (unstimulated) T cells accumulate while waiting to encounter an antigen. Fish_sentence_317

B and T lymphocytes bearing immunoglobulins and T cell receptors, respectively, are found in all jawed fishes. Fish_sentence_318

Indeed, the adaptive immune system as a whole evolved in an ancestor of all jawed vertebrate. Fish_sentence_319

Conservation Fish_section_28

The 2006 IUCN Red List names 1,173 fish species that are threatened with extinction. Fish_sentence_320

Included are species such as Atlantic cod, Devil's Hole pupfish, coelacanths, and great white sharks. Fish_sentence_321

Because fish live underwater they are more difficult to study than terrestrial animals and plants, and information about fish populations is often lacking. Fish_sentence_322

However, freshwater fish seem particularly threatened because they often live in relatively small water bodies. Fish_sentence_323

For example, the Devil's Hole pupfish occupies only a single 3 by 6 metres (10 by 20 ft) pool. Fish_sentence_324

Overfishing Fish_section_29

Main article: Overfishing Fish_sentence_325

Overfishing is a major threat to edible fish such as cod and tuna. Fish_sentence_326

Overfishing eventually causes population (known as stock) collapse because the survivors cannot produce enough young to replace those removed. Fish_sentence_327

Such commercial extinction does not mean that the species is extinct, merely that it can no longer sustain a fishery. Fish_sentence_328

One well-studied example of fishery collapse is the Pacific sardine Sadinops sagax caerulues fishery off the California coast. Fish_sentence_329

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. Fish_sentence_330

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. Fish_sentence_331

In places such as Scotland, Newfoundland, and Alaska the fishing industry is a major employer, so governments are predisposed to support it. Fish_sentence_332

On the other hand, scientists and conservationists push for stringent protection, warning that many stocks could be wiped out within fifty years. Fish_sentence_333

Habitat destruction Fish_section_30

See also: Environmental impact of fishing Fish_sentence_334

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. Fish_sentence_335

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. Fish_sentence_336

Exotic species Fish_section_31

Introduction of non-native species has occurred in many habitats. Fish_sentence_337

One of the best studied examples is the introduction of Nile perch into Lake Victoria in the 1960s. Fish_sentence_338

Nile perch gradually exterminated the lake's 500 endemic cichlid species. Fish_sentence_339

Some of them survive now in captive breeding programmes, but others are probably extinct. Fish_sentence_340

Carp, snakeheads, 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. Fish_sentence_341

Importance to humans Fish_section_32

Economic importance Fish_section_33

Main articles: Fishing industry, Aquaculture, and Fish farming Fish_sentence_342

Throughout history, humans have utilized fish as a food source. Fish_sentence_343

Historically and today, most fish protein has come by means of catching wild fish. Fish_sentence_344

However, aquaculture, or fish farming, which has been practiced since about 3,500 BCE. Fish_sentence_345

in China, is becoming increasingly important in many nations. Fish_sentence_346

Overall, about one-sixth of the world's protein is estimated to be provided by fish. Fish_sentence_347

That proportion is considerably elevated in some developing nations and regions heavily dependent on the sea. Fish_sentence_348

In a similar manner, fish have been tied to trade. Fish_sentence_349

Catching fish for the purpose of food or sport is known as fishing, while the organized effort by humans to catch fish is called a fishery. Fish_sentence_350

Fisheries are a huge global business and provide income for millions of people. Fish_sentence_351

The annual yield from all fisheries worldwide is about 154 million tons, with popular species including herring, cod, anchovy, tuna, flounder, and salmon. Fish_sentence_352

However, the term fishery is broadly applied, and includes more organisms than just fish, such as mollusks and crustaceans, which are often called "fish" when used as food. Fish_sentence_353

Recreation Fish_section_34

Main articles: Fishkeeping, Recreational fishing, and Angling Fish_sentence_354

Fishkeeping Fish_section_35

Fish have been recognized as a source of beauty for almost as long as used for food, appearing in cave art, being raised as ornamental fish in ponds, and displayed in aquariums in homes, offices, or public settings. Fish_sentence_355

Recreational fishing Fish_section_36

Recreational fishing is fishing primarily for pleasure or competition; it can be contrasted with commercial fishing, which is fishing for profit, or subsistence fishing, which is fishing primarily for food. Fish_sentence_356

The most common form of recreational fishing is done with a rod, reel, line, hooks, and any one of a wide range of baits. Fish_sentence_357

Recreational fishing is particularly popular in North America and Europe and state, provincial, and federal government agencies actively management target fish species. Fish_sentence_358

Angling is a method of fishing, specifically the practice of catching fish by means of an "angle" (hook). Fish_sentence_359

Anglers must select the right hook, cast accurately, and retrieve at the right speed while considering water and weather conditions, species, fish response, time of the day, and other factors. Fish_sentence_360

Culture Fish_section_37

Main article: Fish in culture Fish_sentence_361

Fish themes have symbolic significance in many religions. Fish_sentence_362

In ancient Mesopotamia, fish offerings were made to the gods from the very earliest times. Fish_sentence_363

Fish were also a major symbol of Enki, the god of water. Fish_sentence_364

Fish frequently appear as filling motifs in cylinder seals from the Old Babylonian (c. 1830 BC – c. 1531 BC) and Neo-Assyrian (911–609 BC) periods. Fish_sentence_365

Starting during the Kassite Period (c. 1600 BC – c. 1155 BC) and lasting until the early Persian Period (550–30 BC), healers and exorcists dressed in ritual garb resembling the bodies of fish. Fish_sentence_366

During the Seleucid Period (312–63 BC), the legendary Babylonian culture hero Oannes, described by Berossus, was said to have dressed in the skin of a fish. Fish_sentence_367

Fish were sacred to the Syrian goddess Atargatis and, during her festivals, only her priests were permitted to eat them. Fish_sentence_368

In the Book of Jonah, a work of Jewish literature probably written in the fourth century BC, the central figure, a prophet named Jonah, is swallowed by a giant fish after being thrown overboard by the crew of the ship he is travelling on. Fish_sentence_369

The fish later vomits Jonah out on shore after three days. Fish_sentence_370

This book was later included as part of the Hebrew Bible, or Christian Old Testament, and a version of the story it contains is summarized in Surah 37:139-148 of the Quran. Fish_sentence_371

Early Christians used the ichthys, a symbol of a fish, to represent Jesus, because the Greek word for fish, ΙΧΘΥΣ Ichthys, could be used as an acronym for "Ίησοῦς Χριστός, Θεοῦ Υἱός, Σωτήρ" (Iesous Christos, Theou Huios, Soter), meaning "Jesus Christ, Son of God, Saviour". Fish_sentence_372

The gospels also refer to "fishers of men" and feeding the multitude. Fish_sentence_373

In the dhamma of Buddhism, the fish symbolize happiness as they have complete freedom of movement in the water. Fish_sentence_374

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. Fish_sentence_375

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 Hawaiʻi and Matsya of the Hindus. Fish_sentence_376

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_sentence_377

Fish feature prominently in art and literature, in movies such as Finding Nemo and books such as The Old Man and the Sea. Fish_sentence_378

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 and Snakehead Terror. Fish_sentence_379

Piranhas are shown in a similar light to sharks in films such as Piranha; however, contrary to popular belief, the red-bellied piranha is actually a generally timid scavenger species that is unlikely to harm humans. Fish_sentence_380

Legends of half-human, half-fish mermaids have featured in folklore, including the stories of Hans Christian Andersen. Fish_sentence_381

Terminology Fish_section_38

Fish or fishes Fish_section_39

Though often used interchangeably, in biology these words have different meanings. Fish_sentence_382

Fish is used as a singular noun, or as a plural to describe multiple individuals from a single species. Fish_sentence_383

Fishes is used to describe different species or species groups. Fish_sentence_384

Thus a pond would be said to contain 120 fish if all were from a single species or 120 fishes if these included a mix of several species. Fish_sentence_385

The distinction is similar to that between people and peoples. Fish_sentence_386

True fish and finfish Fish_section_40


  • In biology, the term fish is most strictly used to describe any animal with a backbone that has gills throughout life and has limbs, if any, in the shape of fins. Many types of aquatic animals with common names ending in "fish" are not fish in this sense; 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.Fish_item_4_45
  • In fisheries, the term fish is used as a collective term, and includes mollusks, crustaceans and any aquatic animal which is harvested.Fish_item_4_46
  • The strict biological definition of a fish, above, is sometimes called a true fish. True fish are also referred to as finfish or fin fish to distinguish them from other aquatic life harvested in fisheries or aquaculture.Fish_item_4_47

Shoal or school Fish_section_41

Main article: Shoaling and schooling Fish_sentence_387

A random assemblage of fish merely using some localised resource such as food or nesting sites is known simply as an aggregation. Fish_sentence_388

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. Fish_sentence_389

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. Fish_sentence_390

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. Fish_sentence_391

Shoaling and schooling behaviour is believed to provide a variety of advantages. Fish_sentence_392

Examples: Fish_sentence_393


  • Cichlids congregating at lekking sites form an aggregation.Fish_item_5_48
  • Many minnows and characins form shoals.Fish_item_5_49
  • Anchovies, herrings and silversides are classic examples of schooling fish.Fish_item_5_50

While the words "school" and "shoal" have different meanings within biology, the distinctions are often ignored by non-specialists who treat the words as synonyms. Fish_sentence_394

Thus speakers of British English commonly use "shoal" to describe any grouping of fish, and speakers of American English commonly use "school" just as loosely. Fish_sentence_395

See also Fish_section_42

Main article: Outline of fish Fish_sentence_396

For a topical guide to sharks, see Outline of sharks. Fish_sentence_397

Credits to the contents of this page go to the authors of the corresponding Wikipedia page: