Actinopterygii (/ˌæktɪnɒptəˈrɪdʒiaɪ/; from actino- 'having rays' and Ancient Greekπτέρυξ (ptérux) 'wing, fins'), members of which are known as ray-finned fish or actinopterygians, is a class of bony fish[2] that comprise over 50% of living vertebrate species.[3] They are so called because of their lightly built fins made of webbings of skin supported by radially extended thin bony spines called lepidotrichia, as opposed to the bulkier, fleshy lobed fins of the sister class Sarcopterygii (lobe-finned fish). Resembling folding fans, the actinopterygian fins can easily change shape and wetted area, providing superior thrust-to-weight ratios per movement compared to sarcopterygian and chondrichthyian fins. The fin rays attach directly to the proximal or basal skeletal elements, the radials, which represent the articulation between these fins and the internal skeleton (e.g., pelvic and pectoral girdles).
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 and used for buoyancy.[5] Except from the bichirs, which just like the lungs of lobe-finned fish have retained the ancestral condition of ventral budding from the foregut, 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 teleosts 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.[10]
Teleosts and chondrosteans (sturgeons and paddlefish) also differ from the bichirs and holosteans (bowfin and gars) in having gone through a whole-genome duplication (paleopolyploidy). The WGD is estimated to have happened about 320 million years ago in the teleosts, which on average has retained about 17% of the gene duplicates, and around 180 (124–225) million years ago in the chondrosteans. It has since happened again in some teleost lineages, like Salmonidae (80–100 million years ago) and several times independently within the Cyprinidae (in goldfish and common carp as recently as 14 million years ago). [11][12][13][14][15]
Body shapes and fin arrangements
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Ray-finned fish vary in size and shape, in their feeding specializations, and in the number and arrangement of their ray-fins.
Gars (along with the bowfin) are the only surviving members of the Holostei
Reproduction
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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.[16] 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.[17]
Most families use external rather than internal fertilization.[18] Of the oviparous teleosts, most (79%) do not provide parental care.[19]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.[19] The oldest case of viviparity in ray-finned fish is found in Middle Triassic species of †Saurichthys.[20] Viviparity is relatively rare and is found in about 6% of living teleost species; male care is far more common than female care.[19][21] Male territoriality "preadapts" a species for evolving male parental care.[22][23]
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.[24]
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.[26]
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 used to be 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.[33] 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.[33]
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.[34]
^Zhao, W.; Zhang, X.; Jia, G.; Shen, Y.; Zhu, M. (2021). "The Silurian-Devonian boundary in East Yunnan (South China) and the minimum constraint for the lungfish-tetrapod split". Science China Earth Sciences. 64 (10): 1784–1797. Bibcode:2021ScChD..64.1784Z. doi:10.1007/s11430-020-9794-8. S2CID 236438229.
^Kardong, Kenneth (2015). Vertebrates: Comparative Anatomy, Function, Evolution. New York: McGraw-Hill Education. pp. 99–100. ISBN 978-0-07-802302-6.
^Scadeng, Miriam; McKenzie, Christina; He, Weston; Bartsch, Hauke; Dubowitz, David J.; Stec, Dominik; St. Leger, Judy (25 November 2020). "Morphology of the Amazonian Teleost Genus Arapaima Using Advanced 3D Imaging". Frontiers in Physiology. 11: 260. doi:10.3389/fphys.2020.00260. PMC7197331. PMID 32395105.
^Martin, Rene P; Dias, Abigail S; Summers, Adam P; Gerringer, Mackenzie E (16 October 2022). "Bone Density Variation in Rattails (Macrouridae, Gadiformes): Buoyancy, Depth, Body Size, and Feeding". Integrative Organismal Biology. 4 (1): obac044. doi:10.1093/iob/obac044. PMC9652093. PMID 36381998.
^"Actinopterygii Klein, 1885". www.gbif.org. Retrieved 20 September 2021.
^Davesne, Donald; Friedman, Matt; Schmitt, Armin D.; Fernandez, Vincent; Carnevale, Giorgio; Ahlberg, Per E.; Sanchez, Sophie; Benson, Roger B. J. (27 July 2021). "Fossilized cell structures identify an ancient origin for the teleost whole-genome duplication". Proceedings of the National Academy of Sciences. 118 (30). Bibcode:2021PNAS..11801780D. doi:10.1073/pnas.2101780118. PMC8325350. PMID 34301898.
^Parey, Elise; Louis, Alexandra; Montfort, Jerome; Guiguen, Yann; Crollius, Hugues Roest; Berthelot, Camille (12 August 2022). "An atlas of fish genome evolution reveals delayed rediploidization following the teleost whole-genome duplication". Genome Research. 32 (9): 1685–1697. doi:10.1101/gr.276953.122. PMC9528989. PMID 35961774 – via genome.cshlp.org.
^Dorit, R.L.; Walker, W.F.; Barnes, R.D. (1991). Zoology. Saunders College Publishing. p. 819. ISBN 978-0-03-030504-7.
^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.
^Pitcher, T (1993). The Behavior of Teleost Fishes. London: Chapman & Hall.
^ abcReynolds, 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. PMC1692951. PMID 11958696.
^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.
^Clutton-Brock, T. H. (1991). The Evolution of Parental Care. Princeton, NJ: Princeton UP.
^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.
^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. Bibcode:1981EnvBF...6..223B. doi:10.1007/BF00002788. S2CID 19242013.
^Wootton, Robert J.; Smith, Carl (2014). Reproductive Biology of Teleost Fishes. Wiley. ISBN 978-1-118-89139-1.
^Sallan, Lauren C. (February 2014). "Major issues in the origins of ray-finned fish (Actinopterygii) biodiversity". Biological Reviews. 89 (4): 950–971. doi:10.1111/brv.12086. hdl:2027.42/109271. PMID 24612207. S2CID 24876484.
^ abcdThomas 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. PMC3427055. PMID 22869754.
^ abBetancur-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. hdl:2027.42/150563. PMC3644299. PMID 23653398.
^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.
^"Fossilworks: Andreolepis". Archived from the original on 12 February 2010. Retrieved 14 May 2008.
^Henderson, Struan; Dunne, Emma M.; Fasey, Sophie A.; Giles, Sam (3 October 2022). "The early diversification of ray-finned fishes (Actinopterygii): hypotheses, challenges and future prospects". Biological Reviews. 98 (1): 284–315. doi:10.1111/brv.12907. PMC10091770. PMID 36192821. S2CID 241850484.
^Arratia, G. (2015). "Complexities of early teleostei and the evolution of particular morphological structures through time". Copeia. 103 (4): 999–1025. doi:10.1643/CG-14-184. S2CID 85808890.
^Romano, Carlo; Koot, Martha B.; Kogan, Ilja; Brayard, Arnaud; Minikh, Alla V.; Brinkmann, Winand; Bucher, Hugo; Kriwet, Jürgen (February 2016). "Permian-Triassic Osteichthyes (bony fishes): diversity dynamics and body size evolution". Biological Reviews. 91 (1): 106–147. doi:10.1111/brv.12161. PMID 25431138. S2CID 5332637.
^ ab"Chondrosteans: Sturgeon Relatives". paleos.com. Archived from the original on 25 December 2010.
^Theodore Holmes Bullock; Carl D. Hopkins; Arthur N. Popper (2005). Electroreception. Springer Science+Business Media, Incorporated. p. 229. ISBN 978-0-387-28275-6.
^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. PMC5501477. PMID 28683774.
^R. Froese and D. Pauly, ed. (February 2006). "FishBase". Archived from the original on 5 July 2018. Retrieved 8 January 2020.
^Van der Laan, Richard (2016). Family-group names of fossil fishes. doi:10.13140/RG.2.1.2130.1361.
^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.