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![]() Atlantic herring, Clupea harengus The most abundant species of fish in the world. |
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Pteraspidomorphi (early jawless fish) Gnathostomata (jawed vertebrates)
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A fish is a poikilothermic (cold-blooded) water-dwelling vertebrate with gills. There are over 27,000 species of fish, making them the most diverse group of vertebrates. Taxonomically, fish are a paraphyletic group whose exact relationships are much debated; a common division is into the jawless fish (class Agnatha, 75 species including lampreys and hagfish), the cartilaginous fish (class Chondrichthyes, 800 species including sharks and rays), with the remainder classed as bony fish (class Osteichthyes).
Fish come in different sizes, from the 14m (45 ft) whale shark to a 7 mm (just over 1/4 of an inch) long stout infantfish. Many types of aquatic animals named "fish", such as jellyfish and cuttlefish, are not true fish. Other sea dwelling creatures, like dolphins, are actually mammals.
Certain species of fish maintain elevated body temperatures to varying degrees. Endothermic teleosts (bony fishes) are all in the suborder Scombroidei and include the billfishes, tunas, and one species of "primitive" mackerel (Gasterochisma melampus). All sharks in the family Lamnidae – shortfin mako, long fin mako, white, porbeagle, and salmon shark – are known to have the capacity for endothermy, and evidence suggests the trait exists in family Alopiidae (thresher sharks). The degree of endothermy varies from the billfish, which warm only their eyes and brain, to bluefin tuna and porbeagle sharks who maintain body temperatures elevated in excess of 20 °C above ambient water temperatures. See also gigantothermy. Endothermy, though metabolically costly, is thought to provide advantages such as increased contractile force of muscles, higher rates of central nervous system processing, and higher rates of digestion.
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Fish can be found in almost all large bodies of water in salt or brackish or fresh water, at depths from just below the surface to several thousand meters. However, hyper-saline lakes like the Great Salt Lake do not support fishes. Some species of fish have been specially bred to be kept and displayed in an aquarium, and can survive in the home environment.
Catching fish for the purpose of food or sport is known as fishing. The annual yield from all fisheries worldwide is about 100 million tonnes. Overfishing is a threat to many species of fish. On May 15, 2003, the journal Nature reported that all large oceanic fish species worldwide had been so systematically over caught that fewer than 10% of 1950 levels remained. [1] Particularly imperiled were sharks, Atlantic cod, Bluefin tuna, and Pacific sardines. The authors recommended immediate drastic cutbacks in fish catches and reservation of ocean habitats worldwide.
"Fishes" is the proper English plural form of "fish" that biologists use when speaking about two or more fish species, as in "There are over 25,000 fishes in the world" (meaning that there are over 25,000 fish species in the world). When speaking of two or more individual fish organisms, then the word "fish" is used, as in "There are several million fish of the species Gadus morhua" (meaning that G. morhua comprises several million individuals). To see both in action, consider the statement "There are twelve fish in this aquarium, representing five fishes" (meaning that the aquarium contains twelve individuals, some of the same species and some of different species, for a total of five species). The usage of the two words is similar to that of the words "people" and "peoples".
Fishes are an important source of food in many cultures. Other water-dwelling animals such as mollusks, crustaceans, and shellfish are often called "fish" when used as food. For more details, see Fish (food).
Seafood is any sea animal that is served as food or is suitable for eating. This usually includes sea water animals, such as fish and shellfish (including mollusks, and crustaceans). By extension, the term seafood is also applied to similar animals from fresh water. These aquatic animals are also collectively referred to as seafood.
Edible seaweeds are rarely considered seafood, even though they come from sea water and are widely eaten around the world. See Category:Sea vegetables.
The harvesting of seafood is known as fishing and the cultivation of seafood is known as aquaculture or mariculture. Also see fish farming.
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From the earliest age of human civilization, seafood has been an important food source that can easily be hunted and gathered even by those lacking power or speed. Basket-like traps have long been widely used to hunt fish in rivers and lakes. Sometimes, fish was speared just as one would hunt a small animal. Ancient Egyptian civilization used the symbol of fish for counting large numbers and it was eaten both dried and fresh. It is looked over too often but the rise of ancient Greek and Roman civilization was in no small part due to the abundant fish of the Mediterranean Sea. Shellfish was a staple food in many locations and in the Jomon period of Japan; the amount of shellfish consumed and thrown away from that time is used to measure how many people lived in certain area.
Seafood is a source of protein in many diets around the world.