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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 ( /ˌæktɪˌnɒptəˈrɪi/ ) (New Latin, actino- (“having rays”) + Ancient Greek πτέρυξ (ptérux, “wing, fins”)), members of which are known as ray-finned fishes, is a 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).

Numerically, actinopterygians are the dominant class of vertebrates, comprising 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).


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, Dkidney, E swim bladder, F Weberian apparatus, G inner ear, Hbrain, Inostrils, Leye, M gills, Nheart, Ostomach, Pgall bladder, Qspleen, Rinternal sex organs (ovaries or testes), S ventral fins, Tspine, U anal fin, Vtail (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.

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

Fin arrangements

Ray-finned fish are very varied in size and shape, and in the number of their ray-fins and the manner in which they arrange them.


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] Viviparity is relatively rare and is found in about 6% of teleost species; male care is far more common than female care. [7] [8] Male territoriality "preadapts" a species for evolving male parental care. [9] [10]

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. [11]

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. [12]


Actinopterygia is divided into the 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. [13] [14] [15] Approximate dates are from Near et al., 2012. [13]


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. [13]

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. [16] 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. [16]
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. [17]
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
Fossil of a ray-finned perch (Priscacara serrata) from the Lower Eocene about 50 million years ago Priscacara serrata fossil fish (Green River Formation, Lower Eocene; Fossil Lake Basin, southwestern Wyoming, USA) 1 (15335466180).jpg
Fossil of a ray-finned perch ( Priscacara serrata ) from the Lower Eocene about 50 million years ago

The listing below follows Phylogenetic Classification of Bony Fishes [14] [18] with notes when this differs from Nelson, [19] ITIS [20] and FishBase [21] and extinct groups from Van der Laan 2016. [22]

Related Research Articles

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

Osteichthyes, popularly referred to as the bony fish, is a diverse taxonomic group of fish that have skeletons primarily composed of bone tissue, as opposed to 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.


Characiformes is an order of ray-finned fish, comprising the characins and their allies. Grouped in 18 recognized families, more than 2000 different species are described, including the well-known piranha and tetras.


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 is the sister group of Cladistia. Dating back to the Permian period, the Actinopteri comprise the Chondrostei and the Neopterygii. In other words, the Actinopteri include all extant Actinopterygians, minus the Polypteridae (bichirs). The Actinopteri includes:


Neopterygii is a subclass of ray-finned fish (Actinopterygii). Only a few changes occurred during the evolution of neopterygians from the earlier actinopterygians. They appeared sometime in the Late Permian, before the time of the dinosaurs. The neopterygians were a very successful group of fish, because they could 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 are present in all other groups of fish, with the exception of hagfish, neopterygians have lost this sense, even if it has later been re-evolved within Gymnotiformes and catfishes, which possess nonhomologous teleost ampullae.


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.


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


Holostei is a group of bony fish including gars and bowfins. There are eight species divided among two orders: the Amiiformes, represented by a single living species, the bowfin ; and the Lepisosteiformes, represented by seven living species in two genera, the gars. Further species are to be found in the fossil record and the group was thought to be regarded as paraphyletic. However, a recent study proves that the Holostei is a sister group of the Teleostei, both within the Neopterygii. This was found from the morphology of the Holostei, for example presence of a paired vomer. Holosteans are closer to teleosts than are the chondrosteans, the other group intermediate between teleosts and cartilaginous fish, which are regarded as a sister group to the Neopterigii. The spiracles are reduced to vestigial remnants and the bones are lightly ossified. The thick ganoid scales of the gars are more primitive than those of the bowfin.

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.

Protacanthopterygii superorder of fishes

Protacanthopterygii is a ray-finned fish taxon ranked as a superorder of the infraclass Teleostei. They inhabit both marine and freshwater habitats. They appear to have evolved in the Cretaceous or perhaps late Jurassic, originating probably roughly 150 million years ago; fossils of them and the closely related Otocephala are known from throughout the Cretaceous.

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 order of fishes

Pachycormiformes are an extinct order of marine ray-finned fish known from Mesozoic deposits from Eurasia and the Americas. 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 interpreted as stem-teleosts. 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.

The Euteleostei or euteleosts is a clade of bony fishes within the Teleostei that evolved some 240 million years ago. It is divided into the Protacanthopterygii and the Neoteleostei.

Saurichthyiformes order of fishes

Saurichthyiformes is a group of ray-finned fish which existed in Asia, Africa, Australia, Europe and North America, during the late Permian to early Middle Jurassic periods.

Crossognathiformes order of fishes

Crossognathiformes were an extinct order of prehistoric ray-finned fish.

The Otocephala is a clade of bony fishes within the 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. The clade contains the Clupeiformes (herrings) and the Ostariophysi, a group of other orders including the Cypriniformes, Gymnotiformes (knifefish), and Siluriformes (catfish). The Otocephala may also contain the Alepocephaliformes (slickheads), but as yet (2016) without morphological evidence. The clade is sister to the Euteleostei which contains the majority of bony fish alive today. In 2015, Benton and colleagues set a "plausible minimum" date for the origin of the crown Otocephala as about 228.4 million years ago. They argued that since the oldest locality for any diversity of stem teleosts is the Carnian of Polberg bei Lunz, Austria, whose base is 235 million years old, a rough estimate for the Otocephala can be made.

Stomiati subcohort 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.

Anabantiformes order of fishes

The Anabantiformes are an order of freshwater ray-finned fish with two suborders, five families and having at least 207 species. In addition, some authorities expand the order to include the suborder Nandoidei, which includes three families - the Nandidae, Badidae and Pristolepididae - that appear to be closely related to the Anabantiformes. The order, and these three related families, are part of a monophyletic clade which is a sister clade to the Ovalentaria, the other orders in the clade being Synbranchiformes, Carangiformes, Istiophoriformes and Pleuronectiformes. This clade is sometimes referred to as the Carangaria but is left unnamed and unranked in Fishes of the World. This group of fish are found in Asia and Africa, with some species introduced in United States of America.

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

Centriscoidea superfamily of fishes

Centriscoidea is a superfamily of the suborder Aulostomoidei, part of the order which includes the sea horses, piperfishes and dragonets, the Syngnathiformes. They are chareacterised by having the 5-6 anterior vertebrae being elongated and the pelvic fin has a single spine and four rays.


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