Temporal range: Mid Cambrian–Recent
Giant grouper swimming among schools of other fish
Giant grouper swimming among schools of other fish
Head-on view of a red lionfish
Head-on view of a red lionfish
Scientific classificationEdit this classification
Groups included
Jawless fish
Armoured fish
Spiny sharks
Cartilaginous fish
Bony fish
Ray-finned fish
Lobe-finned fish
Cladistically included but traditionally excluded taxa

Fish are gill-bearing aquatic craniate animals that lack limbs with digits. They form a sister group to the tunicates, together forming the olfactores. Included in this definition are the living hagfish, lampreys, and cartilaginous and bony fish as well as various extinct related groups. Tetrapods emerged within lobe-finned fishes, so cladistically they are fish as well. However, traditionally fish are rendered paraphyletic by excluding the tetrapods (i.e., the amphibians, reptiles, birds and mammals which all descended from within the same ancestry). Because in this manner the term "fish" is defined negatively as a paraphyletic group, it is not considered a formal taxonomic grouping in systematic biology, unless it is used in the cladistic sense, including tetrapods.[1][2] The traditional term pisces (also ichthyes) is considered a typological, but not a phylogenetic classification.

The earliest organisms that can be classified as fish were soft-bodied chordates that first appeared during the Cambrian period. Although they lacked a true spine, they possessed notochords which allowed them to be more agile than their invertebrate counterparts. Fish would continue to evolve through the Paleozoic era, diversifying into a wide variety of forms. Many fish of the Paleozoic developed external armor that protected them from predators. The first fish with jaws appeared in the Silurian period, after which many (such as sharks) became formidable marine predators rather than just the prey of arthropods.

Most fish are ectothermic ("cold-blooded"), allowing their body temperatures to vary as ambient temperatures change, though some of the large active swimmers like white shark and tuna can hold a higher core temperature.[3][4]

Fish can communicate in their underwater environments through the use of acoustic communication. Acoustic communication in fish involves the transmission of acoustic signals from one individual of a species to another. The production of sounds as a means of communication among fish is most often used in the context of feeding, aggression or courtship behaviour.[5] The sounds emitted by fish can vary depending on the species and stimulus involved. They 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.[6]

Fish are abundant in most bodies of water. They can be found in nearly all aquatic environments, from high mountain streams (e.g., char and gudgeon) to the abyssal and even hadal depths of the deepest oceans (e.g., gulpers and anglerfish), although no species has yet been documented in the deepest 25% of the ocean. With 33,600 described species, fish exhibit greater species diversity than any other group of vertebrates.[7][8]

Fish are an important resource for humans worldwide, especially as food. Commercial and subsistence fishers hunt fish in wild fisheries (see fishing) or farm them in ponds or in cages in the ocean (see aquaculture). They are also caught by recreational fishers, kept as pets, raised by fishkeepers, and exhibited in public aquaria. Fish have had a role in culture through the ages, serving as deities, religious symbols, and as the subjects of art, books and movies.


Fish, as vertebrata, developed as sister of the tunicata. As the tetrapods emerged deep within the fishes group, as sister of the lungfish, characteristics of fish are typically shared by tetrapods, including having vertebrae and a cranium.

Drawing of animal with large mouth, long tail, very small dorsal fins, and pectoral fins that attach towards the bottom of the body, resembling lizard legs in scale and development.[9]
Dunkleosteus was a gigantic, 10-metre (33 ft) long prehistoric fish of class Placodermi.

Early fish from the fossil record are represented by a group of small, jawless, armored fish known as ostracoderms. Jawless fish lineages are mostly extinct. An extant clade, the lampreys may approximate ancient pre-jawed fish. The first jaws are found in Placodermi fossils. The diversity of jawed vertebrates may indicate the evolutionary advantage of a jawed mouth. It is unclear if the advantage of a hinged jaw is greater biting force, improved respiration, or a combination of factors.

Fish may have evolved from a creature similar to a coral-like sea squirt, whose larvae resemble primitive fish in important ways. The first ancestors of fish may have kept the larval form into adulthood (as some sea squirts do today), although perhaps the reverse is the case.


Fish are a paraphyletic group: that is, any clade containing all fish also contains the tetrapods, which are not fish. For this reason, groups such as the class Pisces seen in older reference works are no longer used in formal classifications.

Leedsichthys (left), of the subclass Actinopterygii, is the largest known fish, with estimates in 2005 putting its maximum size at 16 metres (52 ft).

Traditional classification divides fish into three extant classes, and with extinct forms sometimes classified within the tree, sometimes as their own classes:[10][11]

The above scheme is the one most commonly encountered in non-specialist and general works. Many of the above groups are paraphyletic, in that they have given rise to successive groups: Agnathans are ancestral to Chondrichthyes, who again have given rise to Acanthodiians, the ancestors of Osteichthyes. With the arrival of phylogenetic nomenclature, the fishes has been split up into a more detailed scheme, with the following major groups:

† – indicates extinct taxon
Some palaeontologists contend that because Conodonta are chordates, they are primitive fish. For a fuller treatment of this taxonomy, see the vertebrate article.

The position of hagfish in the phylum Chordata is not settled. Phylogenetic research in 1998 and 1999 supported the idea that the hagfish and the lampreys form a natural group, the Cyclostomata, that is a sister group of the Gnathostomata.[12][13]

The various fish groups account for more than half of vertebrate species. There are almost 28,000 known extant species, of which almost 27,000 are bony fish, with 970 sharks, rays, and chimeras and about 108 hagfish and lampreys.[14] A third of these species fall within the nine largest families; from largest to smallest, these families are Cyprinidae, Gobiidae, Cichlidae, Characidae, Loricariidae, Balitoridae, Serranidae, Labridae, and Scorpaenidae. About 64 families are monotypic, containing only one species. The final total of extant species may grow to exceed 32,500.[15]

Other Languages
Acèh: Eungkôt
Afrikaans: Vis
Alemannisch: Fische
አማርኛ: ዓሣ
Ænglisc: Fisc
Аҧсшәа: Аҧсыӡ
العربية: سمك
aragonés: Pisces
armãneashti: Pescu
অসমীয়া: মাছ
asturianu: Pexe
Atikamekw: Names
Avañe'ẽ: Pira
Aymar aru: Challwa
azərbaycanca: Balıqlar
تۆرکجه: بالیقلار
বাংলা: মাছ
Banjar: Iwak
башҡортса: Балыҡтар
беларуская: Рыбы
беларуская (тарашкевіца)‎: Рыбы
Bikol Central: Sira
Bislama: Fis
български: Риба
Boarisch: Fiisch
བོད་ཡིག: ཉ།
bosanski: Ribe
brezhoneg: Pesk
буряад: Загаһан
català: Peixos
Чӑвашла: Пулă
Cebuano: Isda
chiShona: Hove
Cymraeg: Pysgodyn
dansk: Fisk
Deutsch: Fische
dolnoserbski: Ryby
eesti: Kalad
Ελληνικά: Ψάρι
эрзянь: Калт
español: Pez
Esperanto: Fiŝoj
estremeñu: Peci
euskara: Arrain
فارسی: ماهی
Fiji Hindi: Machhri
føroyskt: Fiskur
français: Poisson
Frysk: Fisken
Gaeilge: Iasc
Gaelg: Eeast
Gàidhlig: Iasg
galego: Peixes
ГӀалгӀай: Чкъаьрий
ગુજરાતી: માછલી
客家語/Hak-kâ-ngî: Ǹg-è
хальмг: Заһсн
한국어: 물고기
Hausa: Kifi
հայերեն: Ձկներ
Արեւմտահայերէն: Ձուկեր
हिन्दी: मछली
hornjoserbsce: Ryby
hrvatski: Ribe
Bahasa Hulontalo: Tola
Ido: Fisho
Ilokano: Ikan
Bahasa Indonesia: Ikan
interlingua: Pisce
ᐃᓄᒃᑎᑐᑦ/inuktitut: ᐃᖃᓗᒃ
Iñupiak: Iqaluk
Ирон: Кæсæгтæ
isiXhosa: Intlanzi
íslenska: Fiskur
italiano: Pesce
עברית: דג
Jawa: Iwak
Kabɩyɛ: Kpakpayaɣ
ಕನ್ನಡ: ಮೀನು
Kapampangan: Asan
ქართული: თევზები
kaszëbsczi: Rëbë
қазақша: Балықтар
kernowek: Pysk
Kiswahili: Samaki
коми: Чери
Kreyòl ayisyen: Pwason
kurdî: Masî
Кыргызча: Балык
кырык мары: Кол
лакку: Чавахъ
ລາວ: ປາ
Latina: Piscis
latviešu: Zivis
Lëtzebuergesch: Fësch
lietuvių: Žuvys
Limburgs: Vèsse
lingála: Mbísi
Lingua Franca Nova: Pex
la .lojban.: finpe
lumbaart: Pès
magyar: Halak
македонски: Риби
Malagasy: Hazandrano
മലയാളം: മത്സ്യം
मराठी: मासा
მარგალური: ჩხომი
مصرى: سمك
Bahasa Melayu: Ikan
Minangkabau: Ikan
Mìng-dĕ̤ng-ngṳ̄: Ngṳ̀
монгол: Загас
မြန်မာဘာသာ: ငါး (တိရစ္ဆာန်)
Nāhuatl: Michin
Dorerin Naoero: Iy
Na Vosa Vakaviti: Ika
Nederlands: Vissen (dieren)
Nedersaksies: Visk
Nēhiyawēwin / ᓀᐦᐃᔭᐍᐏᐣ: ᓇᒣᔅ
नेपाली: माछा
नेपाल भाषा: न्या
日本語: 魚類
Napulitano: Pisce
Nordfriisk: Fasker
norsk: Fisk
norsk nynorsk: Fisk
Nouormand: Paîsson
occitan: Peis
олык марий: Кол
ଓଡ଼ିଆ: ମାଛ
oʻzbekcha/ўзбекча: Baliqlar
ਪੰਜਾਬੀ: ਮੱਛੀ
پنجابی: مچھی
Patois: Fish
Picard: Pichon
Tok Pisin: Pis
Plattdüütsch: Fisch
polski: Ryby
português: Peixe
Qaraqalpaqsha: Balıq
qırımtatarca: Balıq
Ripoarisch: Fesch
română: Pește
Runa Simi: Challwa
русиньскый: Рыбы
русский: Рыбы
саха тыла: Балык
ᱥᱟᱱᱛᱟᱲᱤ: ᱦᱟᱹᱠᱩ
संस्कृतम्: मत्स्याः
Scots: Fish
shqip: Peshqit
sicilianu: Pisci
සිංහල: මාළු
Simple English: Fish
سنڌي: مڇي
slovenščina: Ribe
ślůnski: Ryby
Soomaaliga: Malaay
کوردی: ماسی
Sranantongo: Fisi
српски / srpski: Рибе
srpskohrvatski / српскохрватски: Riba
ၽႃႇသႃႇတႆး : ပႃ
Sunda: Lauk
suomi: Kala
svenska: Fiskar
Tagalog: Isda
தமிழ்: மீன்
Taqbaylit: Aslem
татарча/tatarça: Балыклар
తెలుగు: చేప
ไทย: ปลา
тоҷикӣ: Моҳӣ
ತುಳು: ಮೀನ್
Türkçe: Balık
удмурт: Чорыг
українська: Риби
اردو: مچھلی
Vahcuengh: Duzbya
vèneto: Pesi
vepsän kel’: Kalad
Tiếng Việt:
Volapük: Fit
Võro: Kala
walon: Pexhon
West-Vlams: Visschn
Winaray: Isda
ייִדיש: פיש
Zazaki: Mase
žemaitėška: Žovis
kriyòl gwiyannen: Poson