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Fish

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Great white shark
Great white shark

A fish is a water-dwelling vertebrate with gills that does not alter form, as amphibians do, throughout its life. Most are cold-blooded, although some (like some species of tuna and shark) are warm-blooded. You will find more than 29,000 species of fish, creating them probably the most diverse group of vertebrates. Taxonomically, fish are a paraphyletic group whose precise relationships are a lot debated; a typical division is in to the jawless fish (class Agnatha, 75 species such as lampreys and hagfish), the cartilaginous fish (class Chondrichthyes, 800 species such as sharks and rays), using the remainder classed as bony fish (class Osteichthyes).

Fish are available in various sizes, in the 16 m (51 ft) whale shark to a eight mm (just more than ¼ of an inch) lengthy stout infantfish. Numerous kinds of aquatic animals named “fish” aren’t accurate fish, and within the case of animals like jellyfish and cuttlefish, aren’t even vertebrates. Other marine creatures which have previously been regarded as fish, like dolphins, are really mammals.

Even though most fish are exclusively aquatic and cold-blooded, you will find exceptions to each instances. Fish from numerous various groups have evolved the capacity to reside out from the water for extended periods of time. Of those amphibious fish some like the mudskipper can reside and move about on land for as much as a number of days. Also, particular species of fish preserve elevated physique temperatures to varying degrees. Endothermic teleosts (bony fishes) are all within the suborder Scombroidei and consist of the billfishes, tunas, and 1 species of “primitive” mackerel (Gasterochisma melampus). All sharks within the family members Lamnidae – shortfin mako, lengthy fin mako, white, porbeagle, and salmon shark – are recognized to possess the capacity for endothermy, and proof suggests the trait exists in family members Alopiidae (thresher sharks). The degree of endothermy varies in the billfish, which warm only their eyes and brain, to bluefin tuna and porbeagle sharks who preserve physique temperatures elevated in excess of 20 °C above ambient water temperatures. See also gigantothermy. Endothermy, although metabolically pricey, is believed to supply benefits like elevated contractile force of muscle tissues, greater prices of central nervous method processing, and greater prices of digestion.

Fish are an essential supply of meals in numerous cultures. Other water-dwelling animals like mollusks, crustaceans, and shellfish are frequently known as “fish” when utilized as meals.

Classification

Fish are a paraphyletic group: that’s, any clade containing all fish also consists of the tetrapods, that are not fish. Because of this, groups like the “Class Pisces” noticed in older reference functions are no longer utilized in formal classifications.

Fish are classified in to the following significant groups:

  • Hyperoartia
    • Petromyzontidae (lampreys)
  • Pteraspidomorphi (early jawless fish)
  • Thelodonti
  • Anaspida
  • Cephalaspidomorphi (early jawless fish)
    • Galeaspida
    • Pituriaspida
    • Osteostraci
  • Gnathostomata (jawed vertebrates)
    • Placodermi
    • Chondrichthyes (cartilaginous fish)
    • Acanthodii
    • Osteichthyes (bony fish)
      • Actinopterygii (ray-finned fish)
      • Sarcopterygii (lobe-finned fish)
        • Actinistia (coelacanths)
        • Dipnoi (lungfish)

Some palaeontologists consider that Conodonta are chordates, and so regard them as primitive fish.

Image http://en.wikipedia.org/wiki/File:White_shark.jpg

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia.

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