Fish

: This page is about the animals. For other meanings, please see Fish (disambiguation).

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Conodonta

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Hyperoartia

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:Petromyzontidae (lampreys)

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Pteraspidomorphi (early jawless fish)

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Thelodonti

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Anaspida

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Cephalaspidomorphi (early jawless fish)

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:Galeaspida

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:Pituriaspida

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:Osteostraci

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Gnathostomata (jawed vertebrates)

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:Placodermi

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:Chondrichthyes (cartilaginous fish)

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:Acanthodii

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:Osteichthyes (bony fish)

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::Actinopterygii (ray-finned fish)

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::Sarcopterygii (lobe-finned fish)

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:::Actinistia (coelacanths)

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:::Dipnoi (lungfish)

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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).

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Fish come in different sizes, from the 14 m (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.

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* Certain species of fish maintain elevated body temperatures to varying degrees. The trait is believed to have evolved separately at least five different times as evidenced by differences in morphology. 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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Petromyzontidae: REDIRECT Lamprey...

Lamprey: Geotriinae...

Actinistia: Actinistia is a subclass of mostly fossil lobe-finned fishes. This subclass contains the coelacanths, including the two living coelacanths, the West Indian Ocean coelacanth and the king of the sea....

Fish related Images and Photos (experimental)

Fish	Fish Sea	Fish c.1983	Fish Taco
Fish Tank	Fish Tank	Fish Safari	Fish School
Fish Forever	Fish Tremble	Fish Pier II	Big Fish