About 64 families are monotypic , containing only one species. Secondary gymnovarian ovaries shed ova into the coelom from which they go directly into the oviduct. Most fish exchange gases using gills on either side of the pharynx. However, bony fish have a single gill opening on each side. Amphibious fish such as the mudskipper can live and move about on land for up to several days, [ dubious — discuss ] or live in stagnant or otherwise oxygen depleted water. 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. 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.
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 to utilize "whole-body endothermy", generating heat with its swimming muscles to warm its body while countercurrent exchange as in respiration minimizes heat loss. In the cartilaginous fishes class Chondrichthyes , sharks of the families Lamnidae porbeagle, mackerel, salmon, and great white sharks and Alopiidae thresher sharks exhibit endothermy.
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 reproductive organs include testicles and ovaries. In most species, gonads are paired organs of similar size, which can be partially or totally fused.
In terms of spermatogonia distribution, the structure of teleosts testes has two types: 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 ovaries may be of three types: In the first type, the oocytes are released directly into the coelomic cavity and then enter the ostium , then through the oviduct and are eliminated. Secondary gymnovarian ovaries shed ova into the coelom from which they go directly into the oviduct. In the third type, the oocytes are conveyed to the exterior through the oviduct.
Cystovaries characterize most teleosts, where the ovary lumen has continuity with the oviduct. 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. 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. Examples of oviparous fish include salmon , goldfish , cichlids , tuna , and eels. 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. In these cases, the male is equipped with a pair of modified pelvic fins known as claspers. Marine fish can produce high numbers of eggs which are often released into the open water column.
The eggs have an average diameter of 1 millimetre 0. Egg of catshark mermaids' purse. The newly hatched young of oviparous fish are called larvae. They are usually poorly formed, carry a large yolk sac for nourishment , and are very different in appearance from juvenile and adult specimens. The larval period in oviparous fish is relatively short usually only several weeks , and larvae rapidly grow and change appearance and structure a process termed metamorphosis to become juveniles.
During this transition larvae must switch from their yolk sac to feeding on zooplankton prey, a process which depends on typically inadequate zooplankton density, starving many larvae. In ovoviviparous fish the eggs develop inside the mother's body after internal fertilization but receive little or no nourishment directly from the mother, depending instead on the yolk. Each embryo develops in its own egg. Familiar examples of ovoviviparous fish include guppies , angel sharks , and coelacanths.
Some species of fish are viviparous. In such species the mother retains the eggs and nourishes the embryos. Typically, viviparous fish have a structure analogous to the placenta seen in mammals connecting the mother's blood supply with that of the embryo. Examples of viviparous fish include the surf-perches , splitfins , and lemon shark.
Some viviparous fish exhibit oophagy , in which the developing embryos eat other eggs produced by the mother. This has been observed primarily among sharks, such as the shortfin mako and porbeagle , but is known for a few bony fish as well, such as the halfbeak Nomorhamphus ebrardtii. This behavior is also most commonly found among sharks, such as the grey nurse shark , but has also been reported for Nomorhamphus ebrardtii. Aquarists commonly refer to ovoviviparous and viviparous fish as livebearers.
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. 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.
In a study conducted by Oliveira et al. The sounds emitted by the H. 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. The red drum, Sciaenops ocellatus , produces drumming sounds by vibrating its swimbladder. Ocellatus can produce different calls depending on the stimuli involved.
Like other animals, fish suffer from diseases and parasites. To prevent disease they have a variety of defenses. Non-specific defenses include the skin and scales, as well as the mucus layer secreted by the epidermis that traps and inhibits the growth of microorganisms. 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.
Specific defenses respond to particular pathogens recognised by the fish's body, i. Some species use cleaner fish to remove external parasites. The best known of these are the Bluestreak cleaner wrasses of the genus Labroides found on coral reefs in the Indian and Pacific oceans. These small fish maintain so-called "cleaning stations" where other fish congregate and perform specific movements to attract the attention of the cleaners.
Immune organs vary by type of fish. These fish rely on regions of lymphoid tissue within other organs to produce immune cells. For example, erythrocytes , macrophages and plasma cells are produced in the anterior kidney or pronephros and some areas of the gut where granulocytes mature.
They resemble primitive bone marrow in hagfish. Cartilaginous fish sharks and rays have a more advanced immune system. They have three specialized organs that are unique to Chondrichthyes ; the epigonal organs lymphoid tissue similar to mammalian bone that surround the gonads, the Leydig's organ within the walls of their esophagus, and a spiral valve in their intestine. These organs house typical immune cells granulocytes, lymphocytes and plasma cells.
They also possess an identifiable thymus and a well-developed spleen their most important immune organ where various lymphocytes , plasma cells and macrophages develop and are stored. Chondrostean fish sturgeons, paddlefish, and 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. Their heart is frequently covered with tissue that contains lymphocytes, reticular cells and a small number of macrophages.
The chondrostean kidney is an important hemopoietic organ; where erythrocytes, granulocytes, lymphocytes and macrophages develop. Like chondrostean fish, the major immune tissues of bony fish or teleostei include the kidney especially the anterior kidney , which houses many different immune cells. 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.
Although not confirmed as yet, this system presumably will be where naive unstimulated T cells accumulate while waiting to encounter an antigen. B and T lymphocytes bearing immunoglobulins and T cell receptors , respectively, are found in all jawed fishes. Indeed, the adaptive immune system as a whole evolved in an ancestor of all jawed vertebrate. However, freshwater fish seem particularly threatened because they often live in relatively small water bodies. 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.
The main tension between fisheries science and the fishing industry is that the two groups have different views on the resiliency of fisheries to intensive fishing. In places such as Scotland, Newfoundland, and Alaska the fishing industry is a major employer, so governments are predisposed to support it. 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.
Introduction of non-native species has occurred in many habitats. One of the best studied examples is the introduction of Nile perch into Lake Victoria in the s. Nile perch gradually exterminated the lake's endemic cichlid species. Some of them survive now in captive breeding programmes, but others are probably extinct. 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, BCE.
Overall, about one-sixth of the world's protein is estimated to be provided by fish. In a similar manner, fish have been tied to trade. 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.
Fisheries are a huge global business and provide income for millions of people. 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 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 for pleasure or competition; it can be contrasted with commercial fishing , which is fishing for profit. The most common form of recreational fishing is done with a rod , reel , line , hooks and any one of a wide range of baits. 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.
Fish themes have symbolic significance in many religions. In ancient Mesopotamia , fish offerings were made to the gods from the very earliest times. 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. In the dhamma of Buddhism , the fish symbolize happiness as they have complete freedom of movement in the water.
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. 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 feature prominently in art and literature, in movies such as Finding Nemo and books such as The Old Man and the Sea.
Large fish, particularly sharks, have frequently been the subject of horror movies and thrillers , most notably the novel Jaws , which spawned a series of films of the same name that in turn inspired similar films or parodies such as Shark Tale 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. 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. But if the pond contained a total of fish from three different species, it would be said to contain three fishes. The distinction is similar to that between people and peoples. 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. 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.
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.
From Wikipedia, the free encyclopedia. For fish as eaten by humans, see Fish as food. For other uses, see Fish disambiguation. For the similar monophyletic clade, see Vertebrata. Giant grouper swimming among schools of other fish. Head-on view of a red lionfish. Fish anatomy and Fish physiology. Fish reproduction and Spawn biology.
Egg of bullhead shark. Fish diseases and parasites. Environmental impact of fishing. Fishing industry , Aquaculture , and Fish farming. Fishkeeping , Recreational fishing , and Angling. For a topical guide to sharks, see Outline of sharks.
Angling sport fishing Aquaculture Aquarium Catch and release Deep sea fish Fish acute toxicity syndrome Fish anatomy Fish as food Fish development Fishing fishing for food Fish intelligence Fishkeeping Forage fish Ichthyology List of fish common names List of fish families Marine biology Marine vertebrates Mercury in fish Otolith Bone used for determining the age of a fish Pregnancy fish Seafood Walking fish.
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Females also have a large translucent ovary , situated towards the posterior of the visceral mass. Males do not possess these organs, but instead have a large testis in place of the ovary, and a spermatophoric gland and sac. In mature males, this sac may contain spermatophores , which are placed inside the female's mantle during mating. Like all cephalopods, squid have complex digestive systems. The muscular stomach is found roughly in the midpoint of the visceral mass.
From there, the bolus moves into the caecum for digestion. The caecum, a long, white organ, is found next to the ovary or testis. In mature squid, more priority is given to reproduction such that the stomach and caecum often shrivel up during the later life stages. Finally, food goes to the liver or digestive gland , found at the siphon end, for absorption.
Solid waste is passed out of the rectum. Beside the rectum is the ink sac, which allows a squid to rapidly discharge black ink into the mantle cavity. Squid have three hearts. Two branchial hearts feed the gills, each surrounding the larger systemic heart that pumps blood around the body. Squid blood contains the copper-rich protein hemocyanin for transporting oxygen. The faintly greenish hearts are surrounded by the renal sacs — the main excretory system. The kidneys are difficult to identify and stretch from the hearts located at the posterior side of the ink sac to the liver.
The systemic heart is made of three chambers, a lower ventricle and two upper auricles. The head end bears eight arms and two tentacles, each a form of muscular hydrostat containing many suckers along the edge.
These tentacles do not grow back if severed. In the mature male, one basal half of the left ventral tentacle is hectocotylised — and ends in a copulatory pad rather than suckers. It is used for sexual intercourse.
The mouth is equipped with a sharp, horny beak mainly made of chitin  and cross-linked proteins , and is used to kill and tear prey into manageable pieces. The beak is very robust, but does not contain minerals, unlike the teeth and jaws of many other organisms, including marine species.
The mouth contains the radula the rough tongue common to all molluscs except bivalvia. The eyes, on either side of the head, each contain a hard lens. The image is focused by changing the position of the lens, as in a camera or telescope , rather than changing the shape of the lens, as in the human eye.
Squid appear to have limited hearing. In , sharp, curved claws on the suction cups of squid tentacles cut up the rubber coating on the hull of the USS Stein. The size suggested the largest squid known at the time. In , a large specimen of an abundant  but poorly understood species, Mesonychoteuthis hamiltoni the colossal squid , was discovered.
The kraken is a legendary tentacled monster possibly based on sightings of real giant squid. According to the FAO , the cephalopod catch for was 3,, tonnes 6. Of this, 2,, tonnes, or In English-speaking countries, squid as food is often marketed using the Italian word calamari.
Squid are found abundantly in certain areas, and provide large catches for fisheries. The body can be stuffed whole, cut into flat pieces, or sliced into rings. The arms, tentacles, and ink are also edible; the only parts not eaten are the beak and gladius pen. Squid is a good food source for zinc and manganese , and high in copper ,  selenium , vitamin B 12 , and riboflavin. From Wikipedia, the free encyclopedia.
This article is about cephalopods. For the web proxy, see Squid software. For other uses, see Squid disambiguation. For the video game, see Squids video game. A dissected male specimen of Onykia ingens , showing a nonerect penis the white tubular structure located below most of the other organs. Giant squid , Colossal squid , and Cephalopod size. World Register of Marine Species. An analysis of the motion of the squid, Loligo vulgaris ". Journal of Experimental Biology.
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