Fish are the gill-beirin aquatic craniate ainimals that lack limms wi deegits. Thay form a sister group tae the tunicates, thegither formin the olfactores. Includit in this defineetion are the leevin hagfish, lampers, an cartilaginous an banie fish as weel as various extinct relatit groups. Tetrapods emerged athin lobe-finned fishes, sae cladistically thay are fish as weel. Houiver, tradeetionally fish are rendered paraphyletic bi excludin the tetrapods (i.e., the amphibians, reptiles, birds an mammals). Acause in this manner the term "fish" is defined negatively as a paraphyletic group, it is nae conseedert a formal taxonomic groupin in seestematic biology. The tradeetional term pisces (an aa ichthyes) is conseedert a teepological, but nae a phylogenetic clessification.

Temporal range: Mid Cambrian–Recent
Giant grouper soummin amang schuils o ither fish
Giant grouper soummin amang schuils o ither fish
Heid-on view o a reid lionfish
Heid-on view o a reid lionfish
Scienteefic clessificationEdit this classification
Kinrick: Animalia
Phylum: Chordata
Clade: Olfactores
Subphylum: Vertebrata
Groups included
Jawless fish
Airmoured fish
Spiny sharks
Cartilaginous fish
Banie fish
Ray-finned fish
Lobe-finned fish
Cladeestically includit but tradeetionally excludit taxa

The earliest organisms that can be clessifee'd as fish war saft-bodied chordates that first appeared in the Cambrian period. Awtho thay lacked a true spine, thay possessed notochords that alloued them tae be mair agile nor thair invertebrate coonterpairts. Fish wad conteena tae evolve throu the Paleozoic era, diversifeein intae a wide variety o forms. Mony fish o the Paleozoic developed external airmour that pertectit them frae predators. The first fish wi jaws appeared in the Silurian period, efter that mony (sic as shairks) becam formidable marine predators raither than juist the prey o arthropods.

Maist fish are ectothermic ("cauld-bluidit"), allouin thair bouk temperaturs tae vary as ambient temperaturs cheenge, tho some o the lairge active soummers lik white shark an tuna can hauld a heicher core temperatur.[1][2] Fish are abundant in maist bouks o watter. Thay can be foond in nearly aw aquatic environments, frae heich moontain streams (e.g., Salvelinus an gudgeon) tae the abyssal an even hadal deepths o the deepest oceans (e.g., gulpers an anglerfish). Wi 33,600 descrived species, fish exhibit greater species diversity than ony ither group o vertebrates.[3]

Fish are an important resoorce for humans warldwide, especially as fuid. Commercial an subsistence fishers hunt fish in wild fisheries (see fishin) or ferm them in ponds or in cages in the ocean (see aquacultur). Thay are an aa catcht bi recreautional fishers, kept as pets, raised bi fishkeepers, an exhibitit in public aquaria. Fish hae haed a role in cultur throu the ages, servin as deities, releegious seembols, an as the subjects o airt, beuks an films.


  1. Goldman, K.J. (1997). "Regulation of body temperature in the white shark, Carcharodon carcharias". Journal of Comparative Physiology. B Biochemical Systemic and Environmental Physiology. 167 (6): 423–429. doi:10.1007/s003600050092. Archived frae the original on 6 Apryle 2012. Retrieved 12 October 2011.
  2. Carey, F.G.; Lawson, K.D. (Februar 1973). "Temperature regulation in free-swimming bluefin tuna". Comparative Biochemistry and Physiology A. 44 (2): 375–392. doi:10.1016/0300-9629(73)90490-8.
  3. "FishBase". FishBase. August 2017. Retrieved 31 August 2017.