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Ray-finned fish
Temporal range:
Electric eelRed-bellied piranhaSockeye salmonPeacock flounderAtlantic codSpotted garYellowfin tunaSpotfin lionfishHumpback anglerfishJapanese pineconefishAmerican paddlefishStriped marlinQueen angelfishNorthern pikeSlender-spined porcupine fishLeafy seadragonWels catfishTwo-banded seabream
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Superclass: Osteichthyes
Class: Actinopterygii
Klein, 1885

Actinopterygii (

between these fins and the internal skeleton (e.g., pelvic and pectoral girdles).

The vast majority (~99%) of actinopterygians are

freshwater and marine environments from the deep sea to subterranean waters to the highest mountain streams. Extant species can range in size from Paedocypris, at 8 mm (0.3 in); to the massive ocean sunfish, at 2,300 kg (5,070 lb); and to the long-bodied oarfish
, at 11 m (36 ft).



Ray-finned fishes occur in many variant forms. The main features of typical ray-finned fish are shown in the adjacent diagram. The swim bladder is a more derived structure than the lung and used for buoyancy.[5] Except from the bichirs, which just like the Sarcopterygii (lobe-finned fish) have retained the ancestral condition of ventrally budding lungs, the swim bladder in ray-finned fishes derives from a dorsal bud above the foregut.[6][5] In early forms the swim bladder could still be used for breathing, a trait still present in Holostei (bowfins and gars).[7] In some fish, like the arapaima, the swim bladder has been modified for breathing air again,[8] and in other lineages it have been completely lost.[9]

Ray-finned fishes have many different types of scales; but all

leptoid scales. The outer part of these scales fan out with bony ridges, while the inner part is crossed with fibrous connective tissue. Leptoid scales are thinner and more transparent than other types of scales, and lack the hardened enamel or dentine-like layers found in the scales of many other fish. Unlike ganoid scales, which are found in non-teleost actinopterygians, new scales are added in concentric layers as the fish grows.[10]

Teleosts also differ from other ray-finned fishes in having gone through a whole-genome duplication (paleopolyploidy).[11][12]

Body shapes and fin arrangements

Ray-finned fish vary in size and shape, in their feeding specializations, and in the number and arrangement of their ray-fins.


Three-spined stickleback (Gasterosteus aculeatus) males (red belly) build nests and compete to attract females to lay eggs in them. Males then defend and fan the eggs. Painting by Alexander Francis Lydon, 1879

In nearly all ray-finned fish, the sexes are separate, and in most species the females spawn eggs that are fertilized externally, typically with the male inseminating the eggs after they are laid. Development then proceeds with a free-swimming larval stage.

Protandry, where a fish converts from male to female, is much less common than protogyny.[14]

Most families use external rather than internal fertilization.[15] Of the oviparous teleosts, most (79%) do not provide parental care.[16] Viviparity, ovoviviparity, or some form of parental care for eggs, whether by the male, the female, or both parents is seen in a significant fraction (21%) of the 422 teleost families; no care is likely the ancestral condition.[16] The oldest case of viviparity in ray-finned fish is found in Middle Triassic species of Saurichthys.[17] Viviparity is relatively rare and is found in about 6% of living teleost species; male care is far more common than female care.[16][18] Male territoriality "preadapts" a species for evolving male parental care.[19][20]

There are a few examples of fish that self-fertilise. The mangrove rivulus is an amphibious, simultaneous hermaphrodite, producing both eggs and spawn and having internal fertilisation. This mode of reproduction may be related to the fish's habit of spending long periods out of water in the mangrove forests it inhabits. Males are occasionally produced at temperatures below 19 °C (66 °F) and can fertilise eggs that are then spawned by the female. This maintains genetic variability in a species that is otherwise highly inbred.[21]

Classification and fossil record

Actinopterygii is divided into the classes

Teleostei. During the Mesozoic (Triassic, Jurassic, Cretaceous) and Cenozoic the teleosts in particular diversified widely. As a result, 96% of living fish species are teleosts (40% of all fish species belong to the teleost subgroup Acanthomorpha), while all other groups of actinopterygians represent depauperate lineages.[22]

The classification of ray-finned fishes can be summarized as follows:

  • Cladistia, which include bichirs and reedfish
  • Actinopteri, which include:
    • Chondrostei, which include Acipenseriformes (paddlefishes and sturgeons)
    • Neopterygii, which include:
      • Teleostei (most living fishes)
      • Holostei, which include:
        • Lepisosteiformes (gars)
        • Amiiformes (bowfin)


period.[25] Approximate divergence dates for the different actinopterygian clades (in millions of years, mya) are from Near et al., 2012.[23]

Jawed vertebrates

Sauropsids (reptiles, birds)







Polypteriformes (bichirs, reedfishes)


Acipenseriformes (sturgeons, paddlefishes)


Lepisosteiformes (gars)

Amiiformes (bowfins)

275 mya


310 mya
360 mya
400 mya
('bony fish')



The polypterids (bichirs and reedfish) are the sister lineage of all other actinopterygians, the Acipenseriformes (sturgeons and paddlefishes) are the sister lineage of Neopterygii, and Holostei (bowfin and gars) are the sister lineage of teleosts. The Elopomorpha (eels and tarpons) appear to be the most basal teleosts.[23]

The earliest known


Teleostei than their external appearance might suggest.[30]
electroreception and the ampullae of Lorenzini is present in all other groups of fish, with the exception of hagfish, neopterygians have lost this sense, though it later re-evolved within Gymnotiformes and catfishes, who possess nonhomologous teleost ampullae.[31]
Fossil of the Carboniferous elonichthyiform Elonichthys peltigerus
Fossil of the Permian aeduelliform Aeduella blainvillei
Fossil of the Permian palaeonisciform Palaeoniscum freieslebeni
Fossil of the Triassic bobasatraniiform Bobasatrania canadensis
Fossil of the Triassic perleidiform Thoracopterus magnificus
Fossil of the Jurassic aspidorhynchiform Aspidorhynchus sp.
Fossil of the Jurassic pachycormiform Pachycormus curtus
Fossil of the Cretaceous acipenseriform Yanosteus longidorsalis
Fossil of the Cretaceous aulopiform Nematonotus longispinus
Fossil of the Cretaceous ichthyodectiform Thrissops formosus
Fossil of the Cretaceous carangiform Mene oblonga
pleuronectiform Amphistium paradoxum
Lower Eocene
about 50 million years ago
Fossil of the Miocene syngnathiform Nerophis zapfei
Skeleton of the angler fish, Lophius piscatorius. The first spine of the dorsal fin of the anglerfish is modified so it functions like a fishing rod with a lure
Skeleton of another ray-finned fish, the lingcod
Blue catfish skeleton


The listing below is a summary of all

ITIS[33] and FishBase[34] and extinct groups from Van der Laan 2016[35] and Xu 2021.[36]


  1. S2CID 236438229
  2. .
  3. ^ .
  4. ^ (Davis, Brian 2010).
  5. ^
    PMID 33463017
  6. .
  7. .
  8. .
  9. .
  10. ^ "Actinopterygii Klein, 1885". Retrieved 20 September 2021.
  11. PMID 34301898
  12. – via
  13. .
  14. .
  15. ^ Pitcher, T (1993). The Behavior of Teleost Fishes. London: Chapman & Hall.
  16. ^
    PMID 11958696
  17. .
  18. ^ Clutton-Brock, T. H. (1991). The Evolution of Parental Care. Princeton, NJ: Princeton UP.
  19. PMID 7382520
    . Retrieved 15 September 2013.
  20. .
  21. .
  22. .
  23. ^ .
  24. ^ .
  25. .
  26. ^ "Fossilworks: Andreolepis". Archived from the original on 12 February 2010. Retrieved 14 May 2008.
  27. S2CID 241850484
  28. .
  29. .
  30. ^ a b "Chondrosteans: Sturgeon Relatives". Archived from the original on 25 December 2010.
  31. .
  32. .
  33. ^ "Actinopterygii". Integrated Taxonomic Information System. Retrieved 3 April 2006.
  34. ^ R. Froese and D. Pauly, ed. (February 2006). "FishBase". Archived from the original on 5 July 2018. Retrieved 8 January 2020.
  35. .
  36. .
  37. Polypteriformes is placed in its own subclass Cladistia
  38. Gasterosteiformes

External links