Actinopterygii /ˌæktᵻnˌɒptəˈrɪdʒi.aɪ/, or the ray-finned fishes, constitute a class or subclass of the bony fishes.

The ray-finned fishes are so called because they possess lepidotrichia or "fin rays", their fins being webs of skin supported by bony or horny spines ("rays"), as opposed to the fleshy, lobed fins that characterize the class Sarcopterygiiwhich also, however, possess lepidotrichia. 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).

Numerically, actinopterygians are the dominant class of vertebrates, comprising nearly 99% of the over 30,000 species of fish.[1] 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).



Anatomy of a typical ray-finned fish

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 diagram at the left.


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.[2] 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 transitioning to males at some stage, triggered by some internal or external factor. This may be advantageous as females become less prolific as they age while male fecundity increases with age. Protandry, where a fish transitions from male to female, is much less common than protogyny.[3]

Most families use external rather than internal fertilization.[4] Of the oviparous teleosts, most (79%) do not provide parental care.[5] 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.[5] Viviparity is relatively rare and is found in about 6% of teleost species; male care is far more common than female care.[5][6] Male territoriality "preadapts" a species for evolving male parental care.[7][8]

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.[9]

Fossil recordEdit

See also: Evolution of fish

The earliest known fossil actinopterygiian is Andreolepis hedei, dating back 420 million years (Late Silurian). Remains have been found in Russia, Sweden, and Estonia.[10]


Actinopterygians are divided into the subclasses Chondrostei and Neopterygii. The Neopterygii, in turn, are 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.[11][12][13] Approximate dates are from Near et al., 2012.[11]

Actinopterygii 400 mya

Chondrostei (sturgeons, paddlefishes, reedfishes, bichirs) 

Neopterygii 360 mya

Holostei (bowfins, gars) 275 mya 

Teleostei 310 mya 


Coelacanths, Lungfish





Sauropsids (reptiles, birds) 

The polypterids (bichirs and ropefish) 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) appears to be the most basic teleosts.[11]

Atlantic sturgeon
Chondrostei (cartilage bone) are primarily cartilaginous fish showing some ossification. There are 52 species divided among two orders, the Acipenseriformes (sturgeons and paddlefishes) and the Polypteriformes (reedfishes and bichirs). 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.[14] This group has at times 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.[14] Chondrostei is paraphyletic meaning that this subclass does not contain all the descendants of their common ancestor; reclassification of the Chondrostei is therefore not out of the question.
Atlantic salmon
Neopterygii (new fins) appeared somewhere in the Late Permian, before the time of the dinosaurs. There are only few changes during their evolution from the earlier actinopterygians. They 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, Neopterygii has lost this sense, though it later re-evolved within Gymnotiformes and catfishes, who possess nonhomologous teleost ampullae.[15]

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

Hypsospondylus fossil

The listing below follows Phylogenetic Classification of Bony Fishes [16] with notes when this differs from Nelson,[17] ITIS [18] and FishBase.[19]

  • Subclass Cladistii Pander 1860
    • Order †Guildayichthyiformes Lund 2000
    • Order Polypteriformes (bichirs and reedfishes) [20]
  • Subclass Actinopteri Cope 1972
    • Order †Tarrasiiformes
    • Order †Cheirolepidiformes
    • Order †Paramblypteriformes Heyler 1969
    • Order †Rhadinichthyiformes
    • Order †Phanerorhynchiformes
    • Order †Luganoiiformes Lehman 1958
    • Order †Haplolepidiformes
    • Order †Ptycholepiformes
    • Order †Platysomiformes
    • Order †Palaeonisciformes
    • Order †Pholidopleuriformes
    • Order †Peltopleuriformes
    • Order †Perleidiformes
    • Infra class Chondrostei
      • Order Acipenseriformes (sturgeons and paddlefishes)
      • Order †Saurichthyiformes
    • Infra class Neopterygii Regan 1923
      • Order †Pachycormiformes
      • Holostei
        • Order †Parasemionotiformes Lehman 1966
        • Order †Ionoscopiformes Grande & Bemis 1998
        • Order †Pycnodontiformes Berg 1937
        • Order †Semionotiformes Arambourg & Bertin 1958
        • Order Lepisosteiformes (gars)
        • Order Amiiformes (bowfins)
      • Teleostei Müller 1844
        • Aspidorhynchiformes
        • Pholidophoriformes
        • Leptolepidiformes
        • Teleocephala
          • Megacohort Elopocephalai Patterson 1977 sensu Arratia 1999 (Elopomorpha Greenwood et al. 1966)
            • Order Elopiformes (ladyfishes and tarpon)
            • Order Albuliformes (bonefishes)
            • Order Notacanthiformes (halosaurs and spiny eels)
            • Order Anguilliformes Regan 190 (true eels)
          • Megacohort Osteoglossocephalai sensu Arratia 1999
            • Supercohort Osteoglossocephala sensu Arratia 1999 (Osteoglossomorpha Greenwood et al. 1966)
              • Order †Ichthyodectiformes Bardeck & Sprinkle 1969
              • Order †Lycopteriformes
              • Order Osteoglossiformes (bony-tongued fishes)
              • Order Hiodontiformes (mooneye and goldeye)
            • Supercohort Clupeocephala Patterson & Rosen 1977 sensu Arratia 2010
              • Order †Crossognathiformes Taverne 1989
              • Order †Tselfatiiformes Nelson 1994
              • Cohort Otomorpha (Otocephala; Ostarioclupeomorpha)
                • Subcohort Clupei (Clupeomorpha)
                  • Order †Ellimmichthyiformes Grande 1982
                  • Order Clupeiformes (herrings and anchovies)
                • Subcohort Alepocephali
                  • Order Alepocephaliformes
                • Subcohort Ostariophysi Sagemehl 1885
                  • Section Anotophysa Rosen 1970
                    • Order Gonorynchiformes (milkfishes)
                  • Section Otophysa Garstang 1931
                    • Order Cypriniformes (barbs, carp, danios, goldfishes, loaches, minnows, rasboras)
                    • Order Characiformes (characins, pencilfishes, hatchetfishes, piranhas, tetras, dourado / golden (genus Salminus) and pacu)
                    • Order Gymnotiformes (electric eels and knifefishes)
                    • Order Siluriformes (catfishes)
              • Cohort Euteleosteomorpha (Euteleostei Greenwood 1967 sensu Johnson & Patterson 1996)
                • Subcohort Lepidogalaxii
                  • Lepidogalaxiiformes
                • Subcohort Protacanthopterygii sensu Johnson & Patterson 1996
                  • Order Argentiniformes (barreleyes and slickheads) (formerly in Osmeriformes)
                  • Order Galaxiiformes
                  • Order Salmoniformes (salmon and trout)
                  • Order Esociformes (pike)
                • Subcohort Stomiati
                  • Order Osmeriformes (smelts)
                  • Order Stomiatiformes (bristlemouths and marine hatchetfishes)
                • Subcohort Neoteleostei Nelson 1969
                  • Infracohort Ateleopodia
                    • Order Ateleopodiformes (jellynose fish)
                  • Infracohort Eurypterygia Rosen 1973
                    • Section Aulopa [Cyclosquamata]
                      • Order Aulopiformes (Bombay duck and lancetfishes)
                    • Section Ctenosquamata Rosen 1973
                      • Subsection Myctophata [Scopelomorpha]
                        • Order Myctophiformes (lanternfishes)
                      • Subsection Acanthomorphata
                        • Division Lampridacea [Lampridiomorpha]
                          • Order Lampriformes (oarfish, opah and ribbonfishes)
                        • Division Paracanthomorphacea sensu Grande et al. 2013 (Paracanthopterygii Greenwood 1937)
                          • Order Percopsiformes (cavefishes and trout-perches)
                          • Order †Sphenocephaliformes
                          • Order Zeiformes (dories)
                          • Order Stylephoriformes
                          • Order Gadiformes (cods)
                        • Division Polymixiacea (Polymyxiomorpha)
                          • Order †Pattersonichtyiformes
                          • Order †Ctenothrissiformes
                          • Order Polymixiiformes (beardfishes)
                        • Division Euacanthomorphacea sensu Johnson & Patterson 1993 (Acanthopterygii Gouan 1770 sensu Nelson 1994)
                          • Subdivision Berycimorphaceae
                            • Order Beryciformes (fangtooths and pineconefishes) (incl. Stephanoberyciformes; Cetomimiformes)
                          • Subdivision Holocentrimorphaceae
                            • Order Holocentriformes
                          • Subdivision Percomorphaceae (Percomorpha sensu Miya et al. 2003; Acanthopteri)
                            • Series Ophidiimopharia
                              • Order Ophidiiformes (pearlfishes)
                            • Series Batrachoidimopharia
                              • Order Batrachoidiformes (toadfishes)
                            • Series Gobiomopharia
                              • Order Kurtiformes
                              • Order Gobiiformes
                            • Series Scombrimopharia
                              • Order Syngnathiformes (seahorses and pipefishes[21])
                              • Order Scombriformes
                            • Series Carangimopharia
                              • Sub Series Anabantaria
                                • Order Synbranchiformes (swamp eels)
                                • Order Anabantiformes (Labyrinthici)
                              • Sub Series Carangaria
                                • Carangaria incertae sedis
                                • Order Istiophoriformes
                                • Order Carangiformes
                                • Order Pleuronectiformes (flatfishes)
                              • Sub Series Ovalentaria sensu Smith & Near 2012 (Stiassnyiformes sensu Li et al. 2009)
                                • Ovalentaria incertae sedis
                                • Order Pholidichthyiformes
                                • Order Cichliformes
                                • Order Atheriniformes (silversides and rainbowfishes)
                                • Order Cyprinodontiformes (livebearers, killifishes)
                                • Order Beloniformes (flyingfishes)
                                • Order Mugiliformes (mullets)
                                • Order Blenniiformes [incl. Gobiesociformes [22]]
                            • Series Eupercaria (Percomorpharia)
                              • Eupercaria incertae sedis
                              • Order Labriformes
                              • Order Ephippiformes
                              • Order Lobotiformes
                              • Order Acanthuriformes
                              • Order Chaetodontiformes
                              • Order Spariformes
                              • Order Lophiiformes (anglerfishes)
                              • Order Tetraodontiformes (filefishes and pufferfish)
                              • Order Uranoscopiformes (Paratrachinoidei sensu Li et al. 2009)
                              • Order Pempheriformes
                              • Order Centrarchiformes
                              • Order Perciformes (incl. Gasterosteiformes; Scorpaeniformes)
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