For fish as eaten by humans, see Fish as food.
For other uses, see Fish (disambiguation).
|FishTemporal range: Mid Cambrian–Recent|
|Cladistically included but traditionally excluded taxa|
Fish would continue to evolve through the Paleozoic era, diversifying into a wide variety of forms.
Many fish of the Paleozoic developed external armor that protected them from predators.
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 can communicate in their underwater environments through the use of acoustic communication.
Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another.
The production of sounds as a means of communication among fish is most often used in the context of feeding, aggression or courtship behaviour.
The sounds emitted by fish can vary depending on the species and stimulus involved.
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 are abundant in most bodies of water.
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.
With 34,300 described species, fish exhibit greater species diversity than any other group of vertebrates.
Fish are an important resource for humans worldwide, especially as food.
Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies.
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.
The traditional term pisces (also ichthyes) is considered a , but not a phylogenetic classification.
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.
The English word once had a much broader usage than its current biological meaning.
"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.
Main article: Evolution of fish
Fish, as vertebrata, developed as sister of the tunicata.
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.
Early fish from the fossil record are represented by a group of small, jawless, armored fish known as ostracoderms.
Jawless fish lineages are mostly extinct.
An extant clade, the lampreys may approximate ancient pre-jawed fish.
The first jaws are found in Placodermi fossils.
They lacked distinct teeth, having instead the oral surfaces of their jaw plates modified to serve the various purposes of teeth.
The diversity of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth.
It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination of factors.
Fish may have evolved from a creature similar to a coral-like sea squirt, whose larvae resemble primitive fish in important ways.
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.
For this reason, groups such as the class Pisces seen in older reference works are no longer used in formal classifications.
- Class Agnatha (jawless fish)
- Class Chondrichthyes (cartilaginous fish)
- Class Placodermi (armoured fish) †
- Class Acanthodii ("spiny sharks", sometimes classified under bony fishes)†
- Class Osteichthyes (bony fish)
The above scheme is the one most commonly encountered in non-specialist and general works.
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.
With the arrival of phylogenetic nomenclature, the fishes has been split up into a more detailed scheme, with the following major groups:
- Class Myxini (hagfish)
- Class Pteraspidomorphi † (early jawless fish)
- Class Thelodonti †
- Class Anaspida †
- Class Petromyzontida or Hyperoartia
- Petromyzontidae (lampreys)
- Class Conodonta (conodonts) †
- Class Cephalaspidomorphi † (early jawless fish)
- Infraphylum Gnathostomata (jawed vertebrates)
- Class Placodermi † (armoured fish)
- Class Chondrichthyes (cartilaginous fish)
- Class Acanthodii † (spiny sharks)
- Superclass Osteichthyes (bony fish)
- Class Actinopterygii (ray-finned fish)
- Subclass Chondrostei
- Subclass Neopterygii
- Class Sarcopterygii (lobe-finned fish)
For a fuller treatment of this taxonomy, see the vertebrate article.
The position of hagfish in the phylum Chordata is not settled.
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.
The various fish groups account for more than half of vertebrate species.
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.
Main article: 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.
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.
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.
As paraphyletic groups are no longer recognised in modern systematic biology, the use of the term "fish" as a biological group must be avoided.
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.
However, according to the definition above, all mammals, including cetaceans like whales and dolphins, are not fish.
In some contexts, especially in aquaculture, the true fish are referred to as finfish (or fin fish) to distinguish them from these other animals.
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.
Each criterion has exceptions.
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.
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.
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).
There are even fish that live mostly on land or lay their eggs on land near water.
Mudskippers feed and interact with one another on mudflats and go underwater to hide in their burrows.
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.
Exceptionally rich sites in the Amazon basin, such as Cantão State Park, can contain more freshwater fish species than occur in all of Europe.
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.
Anatomy and physiology
See also: Aquatic respiration
Gills consist of threadlike structures called filaments.
Fish exchange gases by pulling oxygen-rich water through their mouths and pumping it over their gills.
In some fish, capillary blood flows in the opposite direction to the water, causing countercurrent exchange.
The gills push the oxygen-poor water out through openings in the sides of the pharynx.
However, bony fish have a single gill opening on each side.
This opening is hidden beneath a protective bony cover called an operculum.
Fish from multiple groups can live out of the water for extended periods.
Many such fish can breathe air via a variety of mechanisms.
The skin of anguillid eels may absorb oxygen directly.
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.
Mudskippers breathe by absorbing oxygen across the skin (similar to frogs).
A number of fish have evolved so-called accessory breathing organs that extract oxygen from the air.
Breathing air is primarily of use to fish that inhabit shallow, seasonally variable waters where the water's oxygen concentration may seasonally decline.
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.
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.
Air breathing 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.
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.
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, bulbus 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.
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.
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.
Main article: Fish scale
The scales of fish originate from the mesoderm (skin); they may be similar in structure to teeth.
Sensory and nervous system
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.
Fish brains are divided into several regions.
The olfactory lobes are very large in fish that hunt primarily by smell, such as hagfish, sharks, and catfish.
In fish the telencephalon is concerned mostly with olfaction.
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 pineal body lies just above the diencephalon.
This structure detects light, maintains circadian rhythms, and controls color changes.
The hindbrain (or metencephalon) is particularly involved in swimming and balance.
The cerebellum is a single-lobed structure that is typically the biggest part of the brain.
The brain stem (or myelencephalon) is the brain's posterior.
Most fish possess highly developed sense organs.
Nearly all daylight fish have color vision that is at least as good as a human's (see vision in fishes).
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.
Other fish, like the South American electric fishes Gymnotiformes, can produce weak electric currents, which they use in navigation and social communication.
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.
Main article: Vision in fishes
See also: Sensory systems in fish § Hearing
Hearing is an important sensory system for most species of fish.
Further information: Fish intelligence
New research has expanded preconceptions about the cognitive capacities of fish.
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.
Wrasses have also passed the mirror test in a 2018 scientific study.
Capacity for pain
Further information: Pain in fish
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.
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.
Neurons fired in a pattern resembling human neuronal patterns.
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".
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.
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."
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.
Main article: Fish locomotion
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 fish have an internal organ called a swim bladder that adjusts their buoyancy through manipulation of gases.
Although most fish are exclusively ectothermic, there are exceptions.
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.
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.
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).
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.
In most species, gonads are paired organs of similar size, which can be partially or totally fused.
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 fish they are confined to the distal portion of these structures.
Fish ovaries may be of three types: gymnovarian, secondary gymnovarian or cystovarian.
In the third type, the oocytes are conveyed to the exterior through the oviduct.
Cystovaries characterize most teleosts, where the ovary lumen has continuity with the oviduct.
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.
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.
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.
Over 97% of all known fish are oviparous, that is, the eggs develop outside the mother's body.
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.
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.
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 (0.04 in).
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.
Each embryo develops in its own egg.
Some species of fish are viviparous.
In such species the mother retains the eggs and nourishes the embryos.
Some viviparous fish exhibit oophagy, in which the developing embryos eat other eggs produced by the mother.
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.
Acoustic communication in fish
Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another.
The production of sounds as a means of communication among fish is most often used in the context of feeding, aggression or courtship behaviour.
The sounds emitted can vary depending on the species and stimulus involved.
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.
Stridulatory sound producing mechanisms
There are some species of fish that can produce sounds by rubbing or grinding their bones together.
These noises produced by bone-on-bone interactions are known as 'stridulatory sounds'.
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.
This behaviour is most pronounced when the H. is in distress situations. flavolineatum
The grunts produced by this species of fishes generate a frequency of approximately 700 Hz, and last approximately 47 milliseconds.
The H. does not emit sounds with frequencies greater than 1000 Hz, and does not detect sounds that have frequencies greater than 1050 Hz. flavolineatum
In a study conducted by Oliveira et al.
(2014), the longsnout seahorse, Hippocampus reidi, was recorded producing two different categories of sounds; ‘clicks’ and ‘growls’.
The sounds emitted by the H. are accomplished by rubbing their coronet bone across the grooved section of their neurocranium. reidi
‘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.
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.
Growl sounds were produced when the H. encountered stressful situations, such as handling by researchers. reidi
The 'growl' sounds consist of a series of sound pulses and are emitted simultaneously with body vibrations.
Non-stridulatory sound producing mechanisms
Some fish species create noise by engaging specialized muscles that contract and cause swimbladder vibrations.
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.
In addition to short-duration grunts, male toadfishes produce “boat whistle calls”.
These calls are longer in duration, lower in frequency, and are primarily used to attract mates.
The sounds emitted by the O. tao have frequency range of 140 Hz to 260 Hz.
The frequencies of the calls depend on the rate at which the sonic muscles contract.
The red drum, Sciaenops ocellatus, produces drumming sounds by vibrating its swimbladder.
Vibrations are caused by the rapid contraction of sonic muscles that surround the dorsal aspect of the swimbladder.
These vibrations result in repeated sounds with frequencies that range from 100 to >200 Hz.
The S. can produce different calls depending on the stimuli involved. Ocellatus
The sounds created in courtship situations are different from those made during distressing events such as predatorial attacks.
Unlike the males of the S. species, the females of this species don't produce sounds and lack sound-producing (sonic) muscles. Ocellatus
Main article: Fish diseases and parasites
Like other animals, fish suffer from diseases and parasites.
To prevent disease they have a variety of defenses.
Specific defenses respond to particular pathogens recognised by the fish's body, i.e., an immune response.
Some species use cleaner fish to remove external parasites.
These small fish maintain so-called "cleaning stations" where other fish congregate and perform specific movements to attract the attention of the cleaners.
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.
Immune organs vary by type of fish.
These fish rely on regions of lymphoid tissue within other organs to produce immune cells.
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).
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.)
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.
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.
In 2006, a lymphatic system similar to that in mammals was described in one species of teleost fish, the zebrafish.
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 (10 by 20 ft) pool.
Main article: Overfishing
Overfishing is a major threat to edible fish such as cod and tuna.
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.
In places such as Scotland, Newfoundland, and Alaska the fishing industry is a major employer, so governments are predisposed to support it.
On the other hand, scientists and conservationists push for stringent protection, warning that many stocks could be wiped out within fifty years.
See also: Environmental impact of fishing
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.
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.
Introduction of non-native species has occurred in many habitats.
Some of them survive now in captive breeding programmes, but others are probably extinct.
Importance to humans
Throughout history, humans have utilized fish as a food source.
Historically and today, most fish protein has come by means of catching wild fish.
However, aquaculture, or fish farming, which has been practiced since about 3,500 BCE.
in China, is becoming increasingly important in many nations.
Overall, about one-sixth of the world's protein is estimated to be provided by fish.
That proportion is considerably elevated in some developing nations and regions heavily dependent on the sea.
In a similar manner, fish have been tied to trade.
Fisheries are a huge global business and provide income for millions of people.
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.
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.
Recreational fishing is particularly popular in North America and Europe and state, provincial, and federal government agencies actively management target fish species.
Angling is a method of fishing, specifically the practice of catching fish by means of an "angle" (hook).
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.
Main article: Fish in culture
Fish themes have symbolic significance in many religions.
In ancient Mesopotamia, fish offerings were made to the gods from the very earliest times.
Fish were also a major symbol of Enki, the god of water.
Fish were sacred to the Syrian goddess Atargatis and, during her festivals, only her priests were permitted to eat them.
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.
The fish later vomits Jonah out on shore after three days.
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".
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.
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.
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 or fishes
Though often used interchangeably, in biology these words have different meanings.
Fish is used as a singular noun, or as a plural to describe multiple individuals from a single species.
Fishes is used to describe different species or species groups.
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.
The distinction is similar to that between people and peoples.
True fish and finfish
- 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.
- In fisheries, the term fish is used as a collective term, and includes mollusks, crustaceans and any aquatic animal which is harvested.
- 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.
Shoal or school
Main article: Shoaling and schooling
A random assemblage of fish 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.
- Cichlids congregating at lekking sites form an aggregation.
- Many minnows and characins form shoals.
- Anchovies, herrings and silversides are classic examples of schooling fish.
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.
Main article: Outline of fish
For a topical guide to sharks, see Outline of sharks.
Credits to the contents of this page go to the authors of the corresponding Wikipedia page: en.wikipedia.org/wiki/Fish.