Last updated

Ray-finned fish
Temporal range: Late Silurian – recent
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Chordata
Superclass: Osteichthyes
Class: Actinopterygii
Klein, 1885

Actinopterygii /ˌæktɪnɒptəˈrɪi/ (New Latin actino- ('having rays') + Greek πτέρυξ (ptérux 'wing, fins')), members of which are known as ray-finned fishes, is a clade (traditionally class or subclass) of the bony fishes. [1]


The ray-finned fishes are so-called because their fins are webs of skin supported by bony or horny spines (rays), as opposed to the fleshy, lobed fins that characterize the class Sarcopterygii (lobe-finned fish). These actinopterygian fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the link or connection between these fins and the internal skeleton (e.g., pelvic and pectoral girdles).

By species count, actinopterygians dominate the vertebrates, and they comprise nearly 99% of the over 30,000 species of fish. [2] They are ubiquitous throughout freshwater and marine environments from the deep sea 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 the long-bodied oarfish, at 11 m (36 ft). The vast majority of Actinopterygii (~95%) are teleosts.


Anatomy of a typical ray-finned fish (cichlid)
A: dorsal fin, B: fin rays, C: lateral line, D: kidney, E: swim bladder, F: Weberian apparatus, G: inner ear, H: brain, I: nostrils, L: eye, M: gills, N: heart, O: stomach, P: gall bladder, Q: spleen, R: internal sex organs (ovaries or testes), S: ventral fins, T: spine, U: anal fin, V: tail (caudal fin). Possible other parts not shown: barbels, adipose fin, external genitalia (gonopodium) Anatomia dei pesci.jpg
Anatomy of a typical ray-finned fish (cichlid)
A: dorsal fin, B: fin rays, C: lateral line, D: kidney, E: swim bladder, F: Weberian apparatus, G: inner ear, H: brain, I: nostrils, L: eye, M: gills, N: heart, O: stomach, P: gall bladder, Q: spleen, R: internal sex organs (ovaries or testes), S: ventral fins, T: spine, U: anal fin, V: tail (caudal fin). Possible other parts not shown: barbels, adipose fin, external genitalia (gonopodium)

Ray-finned fishes occur in many variant forms. The main features of a typical ray-finned fish are shown in the adjacent diagram. The swim bladder is the more derived structure. [3]

Ray-finned fishes have many different types of scales; but all teleosts, the most advanced actinopterygians, have 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.[ citation needed ]

Ray-finned and lobe-finned fishes, including tetrapods, possessed lungs used for aerial respiration. Only bichirs retain ventrally budding lungs. [3]

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 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 Gasterosteus aculeatus 1879.jpg
Three-spined stickleback 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. [4] However other patterns of ontogeny exist, with one of the commonest being sequential hermaphroditism. In most cases this involves protogyny, fish starting life as females and converting to males at some stage, triggered by some internal or external factor. Protandry, where a fish converts from male to female, is much less common than protogyny. [5]

Most families use external rather than internal fertilization. [6] Of the oviparous teleosts, most (79%) do not provide parental care. [7] 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. [7] The oldest case of viviparity in ray-finned fish is found in Middle Triassic species of Saurichthys . [8] Viviparity is relatively rare and is found in about 6% of living teleost species; male care is far more common than female care. [7] [9] Male territoriality "preadapts" a species for evolving male parental care. [10] [11]

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. [12]

Fossil record

Evolution of ray-finned fish.png

The earliest known fossil actinopterygian is Andreolepis hedei , dating back 420 million years (Late Silurian). Remains have been found in Russia, Sweden, and Estonia. [13]


Actinopterygii is divided into the classes Cladistia and Actinopteri. The latter comprised subclasses Chondrostei and Neopterygii. The Neopterygii, in turn, is divided into the infraclasses Holostei and Teleostei. During the Mesozoic and Cenozoic the teleosts in particular diversified widely, and as a result, 96% of all known fish species are teleosts. The cladogram shows the major groups of actinopterygians and their relationship to the terrestrial vertebrates (tetrapods) that evolved from a related group of fish. [14] [15] [16] Approximate dates are from Near et al., 2012. [14]


Coelacanths, Lungfish Coelacanth flipped.png


Amphibians Deutschlands Amphibien und Reptilien (Salamandra salamdra).jpg


Mammals Phylogenetic tree of marsupials derived from retroposon data (Paucituberculata).png

Sauropsids (reptiles, birds) Zoology of Egypt (1898) (Varanus griseus).png


Polypteriformes (bichirs, reedfishes) Cuvier-105-Polyptere.jpg


Acipenseriformes (sturgeons, paddlefishes) Atlantic sturgeon flipped.jpg


Lepisosteiformes (gars) Longnose gar flipped.jpg

Amiiformes (bowfins) Amia calva 1908 flipped.jpg

275 mya

Teleostei Cyprinus carpio3.jpg

310 mya
360 mya
400 mya

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. [14]

Chondrostei Atlantic sturgeon flipped.jpg
Atlantic sturgeon
Chondrostei (cartilage bone) is a subclass of primarily cartilaginous fish showing some ossification. Earlier definitions of Chondrostei are now known to be paraphyletic, meaning that this subclass does not contain all the descendants of their common ancestor. There were 52 species divided among two orders, the Acipenseriformes (sturgeons and paddlefishes) and the Polypteriformes (reedfishes and bichirs). Reedfish and birchirs are now separated from the Chondrostei into their own sister lineage, the Cladistia. It is thought that the chondrosteans evolved from bony fish but lost the bony hardening of their cartilaginous skeletons, resulting in a lightening of the frame. Elderly chondrosteans show beginnings of ossification of the skeleton, suggesting that this process is delayed rather than lost in these fish. [17] This group had once been classified with the sharks: the similarities are obvious, as not only do the chondrosteans mostly lack bone, but the structure of the jaw is more akin to that of sharks than other bony fish, and both lack scales (excluding the Polypteriforms). Additional shared features include spiracles and, in sturgeons, a heterocercal tail (the vertebrae extend into the larger lobe of the caudal fin). However the fossil record suggests that these fish have more in common with the Teleostei than their external appearance might suggest. [17]
Neopterygii Salmo salar flipped.jpg
Atlantic salmon
Neopterygii (new fins) is a subclass of ray-finned fish that appeared somewhere in the Late Permian. There were only few changes during its evolution from the earlier actinopterygians. Neopterygians are a very successful group of fishes because they can move more rapidly than their ancestors. Their scales and skeletons began to lighten during their evolution, and their jaws became more powerful and efficient. While 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. [18]
Fossil of the Devonian +cheirolepidiform +Cheirolepis canadensis Cheirolepis canadensis.jpg
Fossil of the Devonian cheirolepidiform Cheirolepis canadensis
Fossil of the Carboniferous +elonichthyiform +Elonichthys peltigerus Elonichthys peltigerus.jpg
Fossil of the Carboniferous elonichthyiform Elonichthys peltigerus
Fossil of the Permian +aeduelliform +Aeduella blainvillei Aeduella sp.JPG
Fossil of the Permian aeduelliform Aeduella blainvillei
Fossil of the Permian +palaeonisciform +Palaeoniscum freieslebeni PalaeoniscusFreieslebenensis-NaturalHistoryMuseum-August23-08.jpg
Fossil of the Permian palaeonisciform Palaeoniscum freieslebeni
Fossil of the Triassic +bobasatraniiform +Bobasatrania canadensis Bobasatrania canadensis 1.jpg
Fossil of the Triassic bobasatraniiform Bobasatrania canadensis
Fossil of the Triassic +perleidiform +Thoracopterus magnificus Thoracopterus magnificus.JPG
Fossil of the Triassic perleidiform Thoracopterus magnificus
Fossil of the Jurassic +aspidorhynchiform +Aspidorhynchus sp. Aspidorhynchus sp.jpg
Fossil of the Jurassic aspidorhynchiform Aspidorhynchus sp.
Fossil of the Jurassic +pachycormiform +Pachycormus curtus Pachycormus curtus SMNS 55300.jpg
Fossil of the Jurassic pachycormiform Pachycormus curtus
Fossil of the Cretaceous acipenseriform +Yanosteus longidorsalis Yanosteus longidorsalis MHNT.jpg
Fossil of the Cretaceous acipenseriform Yanosteus longidorsalis
Fossil of the Cretaceous aulopiform +Nematonotus longispinus Nematonotus longispinus.jpg
Fossil of the Cretaceous aulopiform Nematonotus longispinus
Fossil of the Cretaceous +ichthyodectiform +Thrissops formosus Thrissops formosus 3.JPG
Fossil of the Cretaceous ichthyodectiform Thrissops formosus
Fossil of the Cretaceous carangiform +Mene oblonga Mene oblonga 23.JPG
Fossil of the Cretaceous carangiform Mene oblonga
Fossil of the Cretaceous pleuronectiform +Amphistium paradoxum Amphistium.JPG
Fossil of the Cretaceous pleuronectiform Amphistium paradoxum
Fossil of a ray-finned perch (+Priscacara serrata) from the Lower Eocene about 50 million years ago Priscacara serrata FMNH PF13014 img1.jpg
Fossil of a ray-finned perch ( Priscacara serrata ) from the Lower Eocene about 50 million years ago
Fossil of the Miocene syngnathiform +Nerophis zapfei Nerophis (7992564775).jpg
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 Lophius piscatorius MHNT.jpg
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 Lingcodskeleton1600ppx.JPG
Skeleton of another ray-finned fish, the lingcod
Blue catfish skeleton Blue catfish skeleton.jpg
Blue catfish skeleton

The listing below follows Phylogenetic Classification of Bony Fishes [15] [19] with notes when this differs from Nelson, [20] ITIS [21] and FishBase [22] and extinct groups from Van der Laan 2016 and Xu 2021. [23] [24]

Related Research Articles

Osteichthyes Diverse group of fish with skeletons of bone rather than a cartilage

Osteichthyes, popularly referred to as the bony fish, is a diverse taxonomic group of fish that have skeletons primarily composed of bone tissue. They can be contrasted with the Chondrichthyes, which have skeletons primarily composed of cartilage. The vast majority of fish are members of Osteichthyes, which is an extremely diverse and abundant group consisting of 45 orders, and over 435 families and 28,000 species. It is the largest class of vertebrates in existence today. The group Osteichthyes is divided into the ray-finned fish (Actinopterygii) and lobe-finned fish (Sarcopterygii). The oldest known fossils of bony fish are about 420 million years old, which are also transitional fossils, showing a tooth pattern that is in between the tooth rows of sharks and bony fishes.

Amiiformes Extinct order of fishes

The Amiiformes order of fish has only one extant species, the bowfin. These Amiiformes are found in the freshwater systems of North America, in the United States and parts of southern Canada. They live in freshwater streams, rivers, and swamps.

Semionotiformes Extinct order of fishes

Semionotiformes is an order of primitive, ray-finned, primarily freshwater fish from the Triassic to the Cretaceous. The best-known genus is Semionotus of Europe and North America.

Actinopteri Group of fishes

Actinopteri is the sister group of Cladistia in the class Actinopterygii.

Neopterygii Subclass of fishes

Neopterygii is a subclass of ray-finned fish (Actinopterygii). Neopterygii includes the Holostei and the Teleostei, of which the latter compromise the vast majority of extant fishes, and over half of all living vertebrate species. While living holosteans include only freshwater taxa, teleosts are diverse in both freshwater and marine environments. Many new species of teleosts are scientifically described each year.

Elopomorpha Superorder of fishes

The superorder Elopomorpha contains a variety of types of fishes that range from typical silvery-colored species, such as the tarpons and ladyfishes of the Elopiformes and the bonefishes of the Albuliformes, to the long and slender, smooth-bodied eels of the Anguilliformes. The one characteristic uniting this group of fishes is they all have leptocephalus larvae, which are unique to the Elopomorpha. No other fishes have this type of larvae.

Syngnathiformes Order of fishes

The Syngnathiformes are an order of ray-finned fishes that includes the pipefishes and seahorses.

Holostei group of bony fish

Holostei is a group of ray-finned bony fish including gars and bowfins. There are eight living species divided among two orders: the Amiiformes, represented by a single living species, the bowfin ; and the Lepisosteiformes, the gars, represented by seven living species in two genera. Further species are to be found in the fossil record. Fossil species included, the Amiiformes belong to the clade Halecomorphi, whereas Lepisosteiformes are part of Ginglymodi.

Acanthopterygii Superorder of bony fishes

Acanthopterygii is a superorder of bony fishes in the class Actinopterygii. Members of this superorder are sometimes called ray-finned fishes for the characteristic sharp, bony rays in their fins; however this name is often given to the class Actinopterygii as a whole.

Palaeonisciformes Extinct order of fishes

The Palaeonisciformes are an extinct order of early ray-finned fishes (Actinopterygii) which began in the Late Silurian and ended in the Late Cretaceous. The name of the order is derived from the Greek words paleo (ancient) and ὀνίσκος, probably pertaining to the organization of the fishes' scales, similar to the exoskeletal plating of woodlice.

Acanthomorpha is an extraordinarily diverse taxon of teleost fishes with spiny-rays. The clade contains about one third of the world's modern species of vertebrates: over 14,000 species.

Pachycormiformes Extinct order of ray-finned fishes

Pachycormiformes is an extinct order of marine ray-finned fish known from Mesozoic deposits from Eurasia, the Americas and Antarctica. They were characterized by having serrated pectoral fins, reduced pelvic fins and a bony rostrum. Their exact relations with other fish are unclear, but they are generally though to be more closely related to teleosts than to Amiiformes. Pachycormiformes are morphologically diverse, containing both tuna-like carnivorous and edentulous suspension-feeding forms, the latter including the largest ray finned fish known to have existed, Leedsichthys.

Saurichthyiformes Extinct order of fishes

Saurichthyiformes is an extinct order of ray-finned fish which existed in Asia, Africa, Australia, Europe and North America, during the late Permian to early Middle Jurassic. Saurichthyiiformes comprise two families, Saurichthyidae and Yelangichthyidae. Whereas Yelangichthyidae is monotypic, Saurichthyidae includes at least two genera, Saurorhynchus and the very speciose Saurichthys. Additionally, the subgenera Costasaurichthys, Eosaurichthys, Lepidosaurichthys, and Sinosaurichthys are frequently used to group species. Saurichthyiforms were highly successful predators, and with Yelangichthys possibly even included durophagous forms. Species are known from both marine end freshwater deposits. They had their highest diversity during the Early and Middle Triassic.

Crossognathiformes Extinct order of ray-finned fishes

Crossognathiformes is an extinct order of ray-finned fish that lived from the Late Jurassic to the Eocene. Its phylogenetic placement is disputed; some authors have recovered it as part of the teleost stem group, while others place it in a basal position within crown group Teleostei.

Halecomorphi Clade of fishes

Halecomorphi is a taxon of ray-finned bony fish in the clade Neopterygii. The sole living Halecomorph is the bowfin, but the group contains many extinct species in several families in the order Amiiformes, as well as the extinct orders Ionoscopiformes, Panxianichthyiformes, and Parasemionotiformes. The fossil record of halecomorphs goes back at least to the Early Triassic epoch.

Percomorpha Clade of ray-finned fishes

Percomorpha is a large clade of ray-finned fish that includes the tuna, seahorses, gobies, cichlids, flatfish, wrasse, perches, anglerfish, and pufferfish.

Otocephala Clade of ray-finned fishes

Otocephala is a clade of ray-finned fishes within the infraclass Teleostei that evolved some 230 million years ago. It is named for the presence of a hearing (otophysic) link from the swimbladder to the inner ear. Other names proposed for the group include Ostarioclupeomorpha and Otomorpha.

Stomiati Clade of fishes

Stomiati is a group of teleost fish belonging to the cohort (group) Euteleostei, which is a group of bony fishes within the infra-class Teleostei that evolved ~240 million years ago. Teleostei is a group of ray-finned fishes with the exception of primitive bichirs, sturgeons, paddlefishes, freshwater garfishes, and bowfins. The cohort of Euteleostei is divided into two smaller groups: the Protacanthopterygii and the Neoteleostei. Stomiati happen to be descendants of the Protacanthopterygii, and contains the order of Osmeriformes and Stomiiformes.

<i>Amia</i> (fish) Genus of ray-finned fishes

Amia, commonly called bowfin, is a genus of bony fish related to gars in the infraclass Holostei. They are regarded as taxonomic relicts, being the sole surviving species of the order Amiiformes, which dates from the Jurassic to the Eocene, persisting to the present. There is one living species in Amia, Amia calva, and a number of extinct species which have been described from the fossil record.

Trachichthyiformes Order of fishes

The Trachichthyiformes are an order of ray-finned fishes in the superorder Acanthopterygii.


  1. Kardong, Kenneth (2015). Vertebrates: Comparative Anatomy, Function, Evolution. New York: McGraw-Hill Education. pp. 99–100. ISBN   978-0-07-802302-6.
  2. (Davis, Brian 2010).
  3. 1 2 Funk, Emily; Breen, Catriona; Sanketi, Bhargav; Kurpios, Natasza; McCune, Amy (2020). "Changing in Nkx2.1, Sox2, Bmp4, and Bmp16 expression underlying the lung-to-gas bladder evolutionary transition in ray-finned fishes". Evolution & Development. 22 (5): 384–402. doi:10.1111/ede.12354. PMC   8013215 . PMID   33463017.
  4. Dorit, R.L.; Walker, W.F.; Barnes, R.D. (1991). Zoology . Saunders College Publishing. p.  819. ISBN   978-0-03-030504-7.
  5. Avise, J.C.; Mank, J.E. (2009). "Evolutionary perspectives on hermaphroditism in fishes". Sexual Development. 3 (2–3): 152–163. doi:10.1159/000223079. PMID   19684459. S2CID   22712745.
  6. Pitcher, T (1993). The Behavior of Teleost Fishes. London: Chapman & Hall.
  7. 1 2 3 Reynolds, John; Nicholas B. Goodwin; Robert P. Freckleton (19 March 2002). "Evolutionary Transitions in Parental Care and Live Bearing in Vertebrates". Philosophical Transactions of the Royal Society B: Biological Sciences. 357 (1419): 269–281. doi:10.1098/rstb.2001.0930. PMC   1692951 . PMID   11958696.
  8. Maxwell; et al. (2018). "Re‐evaluation of the ontogeny and reproductive biology of the Triassic fish Saurichthys (Actinopterygii, Saurichthyidae)". Palaeontology. 61: 559–574. doi:10.5061/dryad.vc8h5.
  9. Clutton-Brock, T. H. (1991). The Evolution of Parental Care. Princeton, NJ: Princeton UP.
  10. Werren, John; Mart R. Gross; Richard Shine (1980). "Paternity and the evolution of male parentage". Journal of Theoretical Biology. 82 (4): 619–631. doi:10.1016/0022-5193(80)90182-4. PMID   7382520 . Retrieved 15 September 2013.
  11. Baylis, Jeffrey (1981). "The Evolution of Parental Care in Fishes, with reference to Darwin's rule of male sexual selection". Environmental Biology of Fishes. 6 (2): 223–251. doi:10.1007/BF00002788. S2CID   19242013.
  12. Wootton, Robert J.; Smith, Carl (2014). Reproductive Biology of Teleost Fishes. Wiley. ISBN   978-1-118-89139-1.
  13. "Fossilworks: Andreolepis". Archived from the original on 12 February 2010. Retrieved 14 May 2008.
  14. 1 2 3 Thomas J. Near; et al. (2012). "Resolution of ray-finned fish phylogeny and timing of diversification". PNAS. 109 (34): 13698–13703. Bibcode:2012PNAS..10913698N. doi: 10.1073/pnas.1206625109 . PMC   3427055 . PMID   22869754.
  15. 1 2 Betancur-R, Ricardo; et al. (2013). "The Tree of Life and a New Classification of Bony Fishes". PLOS Currents Tree of Life. 5 (Edition 1). doi:10.1371/currents.tol.53ba26640df0ccaee75bb165c8c26288. PMC   3644299 . PMID   23653398. Archived from the original on 13 October 2013.
  16. Laurin, M.; Reisz, R.R. (1995). "A reevaluation of early amniote phylogeny". Zoological Journal of the Linnean Society. 113 (2): 165–223. doi:10.1111/j.1096-3642.1995.tb00932.x.
  17. 1 2 "Chondrosteans: Sturgeon Relatives". Archived from the original on 25 December 2010.
  18. Theodore Holmes Bullock; Carl D. Hopkins; Arthur N. Popper (2005). Electroreception. Springer Science+Business Media, Incorporated. p. 229. ISBN   978-0-387-28275-6.
  19. Betancur-Rodriguez; et al. (2017). "Phylogenetic Classification of Bony Fishes Version 4". BMC Evolutionary Biology. 17 (1): 162. doi:10.1186/s12862-017-0958-3. PMC   5501477 . PMID   28683774.
  20. Nelson, Joseph, S. (2016). Fishes of the World. John Wiley & Sons, Inc. ISBN   978-1-118-34233-6.
  21. "Actinopterygii". Integrated Taxonomic Information System . Retrieved 3 April 2006.
  22. R. Froese and D. Pauly, editors (February 2006). "FishBase". Archived from the original on 5 July 2018. Retrieved 8 January 2020.
  23. Van der Laan, Richard (2016). Family-group names of fossil fishes. doi:10.13140/RG.2.1.2130.1361.
  24. Xu, Guang-Hui (9 January 2021). "A new stem-neopterygian fish from the Middle Triassic (Anisian) of Yunnan, China, with a reassessment of the relationships of early neopterygian clades". Zoological Journal of the Linnean Society. 191 (2): 375–394. doi:10.1093/zoolinnean/zlaa053. ISSN   0024-4082.
  25. In Nelson, Polypteriformes is placed in its own subclass Cladistia.
  26. In Nelson and ITIS, Syngnathiformes is placed as the suborder Syngnathoidei of the order Gasterosteiformes.