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Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity clade of vertebrate that have primarily composed of bone tissue. They can be contrasted with the Chondrichthyes (cartilaginous fish) and the extinct and , which have endoskeletons primarily composed of cartilage. The vast majority of extant taxon fish are members of Osteichthyes, being an extremely diverse and abundant group consisting of 45 orders, over 435 families and 28,000 species. Bony fishes SeaWorld. Retrieved 2 February 2013.
The group is divided into two main , the ray-finned fish (Actinopterygii, which makes up the vast majority of extant fish) and the lobe-finned fish (Sarcopterygii, which gave rise to all land vertebrates, i.e. ). The oldest known of bony fish are about 425 million years old from the late Silurian, which are also transitional fossils showing a dentition that is in between the tooth rows of and true bony fishes. Despite the name, these early basal bony fish had not yet evolved ossification and their skeletons were still mostly cartilaginous, and the main distinguishing feature that set them apart from other fish clades were the development of lung bud that eventually evolved into the and , respectively.
Osteichthyes is broadly equivalent to Euteleostomi. In paleontology the terms are synonymous. In ichthyology the difference is that Euteleostomi presents a cladistic view which includes the terrestrial tetrapods that evolved from lobe-finned fish. Until recently, the view of most ichthyologists has been that Osteichthyes were paraphyletic and include only fishes. However, since 2013 widely cited ichthyology papers have been published with phylogenetic trees that treat the Osteichthyes as a clade including tetrapods.Betancur-R, R., Wiley, E.O., Arratia, G., Acero, A., Bailly, N., Miya, M., Lecointre, G. and Orti, G. (2017) "Phylogenetic classification of bony fishes". BMC evolutionary biology, 17(1): 162. .Hughes, L.C., Ortí, G., Huang, Y., Sun, Y., Baldwin, C.C., Thompson, A.W., Arcila, D., Betancur-R, R., Li, C., Becker, L. and Bellora, N. (2018) "Comprehensive phylogeny of ray-finned fishes (Actinopterygii) based on transcriptomic and genomic data". Proceedings of the National Academy of Sciences, 115(24): 6249–6254. .
Early bony fish had simple lung bud (an outpouching on either side of the esophagus) which helped them breathe air in low-oxygen water as a form of supplementary enteral respiration. In ray-finned fish these have evolved into , the changing sizes of which help to alter the body's specific density and buoyancy. In , a crown group of lobe-finned fish that gave rise to the land-dwelling , these respiratory diverticula became further specialized for obligated air breathing and evolved into the modern amphibian, Reptile, bird and . Early bony fish did not have lepidotrichia like most modern fish, but instead had the fleshy paddle-like fins similar to other non-bony clades of fish, although the lobe-finned fish evolved joint appendicular skeletons within their paired fins, which gave rise to tetrapods' limbs. They also evolved a pair of opercula (gill covers), which can actively draw water across the fish gill so they can breathe without having to swim.
Bony fish do not have placoid scales like cartilaginous fish, but instead have scales that lie underneath the epidermis and do not penetrate it. The three categories of scales in Osteichthyes are cosmoid scales, ganoid scales, and teleost scales. Teleost scales are then divided into two subgroups which are cycloid scales and ctenoid scales. All of these scales have a base of bone that they all originate from; the main difference is that teleost scales have only one layer of bone. Ganoid scales have lamellar bone, and vascular bone that lies on top of the lamellar bone, then enamel that lies on top of both layers of bone. Cosmoid scales have the same two layers of bone that ganoid scales have except that they have dentin in between the enamel and vascular bone.
This has given way to the current Cladistics classification which splits the Osteichthyes into several clades. Under this scheme Osteichthyes is monophyletic, as it includes the tetrapods making it a synonym of the clade Euteleostomi. Most bony fish belong to the ray-finned fish (Actinopterygii).
In ichthyology the difference between Euteleostomi and Osteichthyes is that the former presents a cladistic view, i.e. that the terrestrial Tetrapod evolved from lobe-finned fish (Sarcopterygii). Until recently, the view of most ichthyologists has been that Osteichthyes were paraphyletic and include only bony fishes. However, since 2013 widely cited ichthyology papers have been published with phylogenetic trees that treat the Osteichthyes as a clade including tetrapods, making the terms Euteleostomi and Osteichthyes synonymous.Betancur-R, R., Wiley, E.O., Arratia, G., Acero, A., Bailly, N., Miya, M., Lecointre, G. and Orti, G. (2017) "Phylogenetic classification of bony fishes". BMC evolutionary biology, 17(1): 162. .Hughes, L.C., Ortí, G., Huang, Y., Sun, Y., Baldwin, C.C., Thompson, A.W., Arcila, D., Betancur-R, R., Li, C., Becker, L. and Bellora, N. (2018) "Comprehensive phylogeny of ray-finned fishes (Actinopterygii) based on transcriptomic and genomic data". Proceedings of the National Academy of Sciences, 115(24): 6249–6254. .
Osteichthyes are primitively ectothermic (cold blooded), meaning that their body temperature is dependent on that of the water. But some of the larger marine osteichthyids, such as the opah,Wegner, Nicholas C., Snodgrass, Owen E., Dewar, Heidi, John, Hyde R. Science. "Whole-body endothermy in a mesopelagic fish, the opah, Lampris guttatus". pp. 786–789. Retrieved May 14, 2015. "Warm Blood Makes Opah an Agile Predator". Fisheries Resources Division of the Southwest Fisheries Science Center of the National Oceanic and Atmospheric Administration. May 12, 2015. Retrieved May 15, 2015. "New research by NOAA Fisheries has revealed the opah, or moonfish, as the first fully warm-blooded fish that circulates heated blood throughout its body..." swordfishFritsches, K.A., Brill, R.W., and Warrant, E.J. 2005. Warm Eyes Provide Superior Vision in Swordfishes. Current Biology 15: 55−58Hopkin, M. (2005). Swordfish heat their eyes for better vision. Nature, 10 January 2005 and tuna have independently evolved various levels of endothermy. Bony fish can be any type of heterotroph: numerous species of omnivore, carnivore, herbivore, filter-feeder, detritivore, or hematophage are documented.
Some bony fish are , and a number of species exhibit parthenogenesis. Fertilization is usually external, but can be internal. Development is usually oviparous (egg-laying) but can be Ovoviviparity, or Viviparity. Although there is usually no parental care after birth, before birth parents may scatter, hide, guard or brood eggs, with sea horses being notable in that the males undergo a form of "pregnancy", brooding eggs deposited in a ventral pouch by a female.
The longest is the Giant oarfish, a type of oarfish. Other very large bony fish include the Atlantic blue marlin, some specimens of which have been recorded as in excess of , the black marlin, some sturgeon species, and the Giant grouper and goliath grouper, both of which can exceed in weight. In contrast, Paedocypris progenetica and the stout infantfish can measure less than .
The beluga sturgeon is the largest species of freshwater bony fish extant today, and Arapaima gigas is among the largest of the freshwater fish. The largest bony fish ever was Leedsichthys, which dwarfed the beluga sturgeon as well as the ocean sunfish, giant grouper and all the other giant bony fishes alive today.
Characteristics
Bony fish are characterized by a relatively stable pattern of , rooted, medial insertion of Mandible muscle in the lower jaw. The head and are covered with large dermal bones. The eyeball is supported by a sclerotic ring of four small bones, but this characteristic has been lost or modified in many modern species. The labyrinth in the inner ear contains large . The braincase, or neurocranium, is frequently divided into anterior and posterior sections divided by a fissure.
Classification
Traditionally, Osteichthyes was considered a class, recognised on the presence of a swim bladder, only three pairs of hidden behind a bony operculum, and a predominantly bony skeleton. Under this classification system, Osteichthyes was considered paraphyletic with regard to tetrapoda, as the common ancestor of all osteichthyans includes amongst its descendants. While the largest subclass, Actinopterygii (ray-finned fish), is monophyletic, with the inclusion of the smaller subclass Sarcopterygii, Osteichthyes was regarded as paraphyletic.
Phylogeny
A phylogeny of living Osteichthyes, including the tetrapods, is shown in the cladogram below. Whole-genome duplication took place in the ancestral Osteichthyes.
Biology
All bony fish possess gills. For the majority this is their sole or main means of respiration. Lungfish and other osteichthyan species are capable of respiration through lungs or vascularized swim bladders. Other species can respire through their skin, intestines, and/or stomach.
Examples
The giant sunfish is the heaviest bony fish in the world. In late 2021, Portuguese fishermen found a dead sunfish near the coast of Faial Island, Azores. At in weight, in height, and in length, it was the biggest giant sunfish ever captured.
Liston, J., Newbrey, M., Challands, T., and Adams, C., 2013 (2025). 9783899371598, Verlag Dr. Friedrich Pfeil. ISBN 9783899371598
Comparison with cartilaginous fishes
+ Comparison of cartilaginous and bony fishes Based on: Kotpal R. L. (2010) Modern Text Book Of Zoology Vertebrates Pages 193. Rastogi Publications. .
Habitat Mainly marine Marine and freshwater Shape Usually dorso-ventrally flattened Usually bilaterally flattened Exoskeleton Separate dermal Overlapping dermal cosmoid scale, ganoid scale, cycloid scale or Endoskeleton Cartilaginous Mostly bony Caudal fin Heterocercal Heterocercal or diphycercal Usually posterior. Mostly anterior, occasionally posterior. Intromittent organ Males use as for transferring sperm to a female Do not use claspers, though some species use their as gonopodium for the same purpose Mouth Large, crescent shaped on the ventral side of the head Variable shape and size at the tip or terminal part of the head Fish jaw Hyostylic Hyostylic and autostylic Fish gill Usually five pairs of which are not protected by an operculum. Five pairs of gill slits protected by an operculum (a lateral flap of skin). Fish gill Larnellibranch with long interbranchial septum Leaf shape with reduced interbranchial septum Spiracles The first gill slit usually becomes spiracles opening behind the eyes. No spiracles Branchial arch vessels Five pairs from ventral aorta to gills Only four pairs Branchial arch vessels Nine pairs Four pairs Conus arteriosus Present in heart Absent Cloaca A true cloaca is present only in cartilaginous fishes and . In most bony fishes, the cloaca is absent, and the anus, urinary and genital apertures open separately Stomach Typically J-shaped Shape variable. Absent in some. Intestine Short with spiral valve in lumen Long with no spiral valve Rectal gland Present Absent Liver Usually has two Liver lobe Usually has three lobes Swim bladder Absent Usually present Brain Has large Olfactory bulb and cerebrum with small optic lobes and cerebellum Has small olfactory lobes and cerebrum and large optic lobes and cerebellum Restiform body Present in brain Absent Ductus endolymphaticus Opens on top of head Does not open to exterior Retina Lacks Cone cell Most fish have double cones, a pair of cone cells joined to each other. Accommodation of eye Accommodate for near vision by moving the lens closer to the retina Accommodate for distance vision by moving the lens further from the retina Ampullae of Lorenzini Present Absent Male genital duct Connects to the anterior part of the genital kidney No connection to kidney Not connected to ovaries Connected to ovaries Urinary and genital apertures United and urinogenital apertures lead into common cloaca Separate and open independently to exterior A small number of large eggs with plenty of yolk A large number of small eggs with little yolk Fertilisation Internal Usually external Development Ovoviviparous types develop internally. Oviparous types develop externally using egg cases Normally develop externally without an egg case
See also
Sources
(1997). 9780865422568, Blackwell Sciences. ISBN 9780865422568
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