Osteichthyes /ˌɒstiːˈɪkθi.iːz/, 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
ago, which are also transitional fossils, showing a tooth pattern that
is in between the tooth rows of sharks and bony fishes.
Osteichthyes can be compared 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, whereas on a traditional
Osteichthyes includes only fishes and is therefore paraphyletic.
However, recently published phylogenetic trees treat the Osteichthyes
as a clade.
6 Comparison with cartilaginous fishes
7 See also
Guiyu oneiros, the earliest known bony fish, lived during the Late
Silurian, 419 million years ago). It has the combination of
both ray-finned and lobe-finned features, although analysis of the
totality of its features place it closer to lobe-finned
Bony fish are characterized by a relatively stable pattern of cranial
bones, rooted, medial insertion of mandibular muscle in the lower jaw.
The head and pectoral girdles 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 otoliths. The braincase, or
neurocranium, is frequently divided into anterior and posterior
sections divided by a fissure.
Early bony fish had simple lungs (a pouch on either side of the
esophagus) which helped them breathe in low-oxygen water. In many bony
fish these have evolved into swim bladders, which help the body create
a neutral balance between sinking and floating. (The lungs of
amphibians, reptiles, birds, and mammals were inherited from their
bony fish ancestors.)  They do not have fin spines, but
instead support the fin with lepidotrichia (bone fin rays). They also
have an operculum, which helps them breathe without having to swim.
Bony fish have no placoid scales. Mucus glands coat the body. Most
have smooth and overlapping ganoid, cycloid or ctenoid scales.
Osteichthyes is considered a class, recognised on
having a swim bladder, only three pairs of gill arches, hidden behind
a bony operculum and a predominately bony skeleton. Under this
classification systems, the
Osteichthyes are paraphyletic with regard
to land vertebrates as the common ancestor of all Osteichthyes
includes tetrapods amongst its descendants. The largest subclass, the
Actinopterygii (ray-finned fish) are monophyletic, but with the
inclusion of the smaller sub-class Sarcopterygii,
This has led to an alternative classification, splitting the
Osteichthyes into two full classes. Paradoxically,
under this scheme monophyletic, as it includes the tetrapods, making
it a synonym of the clade Euteleostomi. Most bony fish belong to the
ray-finned fish (Actinopterygii).
Actinopterygii, or 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
Sarcopterygii which also
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). In terms of numbers,
actinopterygians are the dominant class of vertebrates, comprising
nearly 99% of the over 30,000 species of fish (Davis, Brian 2010).
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, to at least 11 m (36 ft).
Sarcopterygii (fleshy fin) or lobe-finned fish constitute a clade
(traditionally a class or subclass of fish only, i.e. excluding the
tetrapods) of the bony fish, though a strict cladistic view includes
the terrestrial vertebrates. The living sarcopterygians are the
coelacanths, lungfish, and the tetrapods. Early lobe-finned fishes had
fleshy, lobed, paired fins, joined to the body by a single bone.
Their fins differ from those of all other fish in that each is borne
on a fleshy, lobelike, scaly stalk extending from the body. Pectoral
and pelvic fins have articulations resembling those of tetrapod limbs.
These fins evolved into legs of the first tetrapod land vertebrates,
amphibians. They also possess two dorsal fins with separate bases, as
opposed to the single dorsal fin of actinopterygians (ray-finned
fish). The braincase of sarcoptergygians primitively has a hinge line,
but this is lost in tetrapods and lungfish. Many early lobe-finned
fishes have a symmetrical tail. All lobe-finned fishes possess teeth
covered with true enamel.
The phylogeny of living bony fishes is shown in the
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
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,
swordfish 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 or
detritivore are documented.
Some bony fish are hermaphrodites, and a number of species exhibit
parthenogenesis. Fertilization is usually external, but can be
internal. Development is usually oviparous (egg-laying) but can be
ovoviviparous, or viviparous. 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
The ocean sunfish is the heaviest bony fish in the world, while
the longest is the king of herrings, a type of oarfish. Specimens of
ocean sunfish have been observed up to 3.3 metres (11 ft) in
length and weighing up to 2,303 kilograms (5,077 lb). Other very
large bony fish include the Atlantic blue marlin, some specimens of
which have been recorded as in excess of 820 kilograms
(1,810 lb), the black marlin, some sturgeon species, and the
giant and goliath grouper, which both can exceed 300 kilograms
(660 lb) in weight. In contrast, the dwarf pygmy goby measures a
minute 15 millimetres (0.59 in).
Arapaima gigas is the largest species of freshwater bony fish. The
largest bony fish ever was Leedsichthys, which dwarfed the beluga
sturgeon, ocean sunfish, giant grouper, and all the other giant bony
fishes alive today.
Comparison with cartilaginous fishes
Cartilaginous fishes can be further divided into sharks, rays and
chimaeras. In the table below, the comparison is made between sharks
and bony fishes. For the further differences with rays, see sharks
Comparison of cartilaginous and bony fishes 
Marine and freshwater
Usually dorso-ventrally flattened
Usually bilaterally flattened
Separate dermal placoid scales
Overlapping dermal cosmoid, ganoid, cycloid or ctenoid scales
Heterocercal or diphycercal
Mostly anterior, occasionally posterior.
Males use pelvic fins as claspers for transferring sperm to a female
Do not use claspers, though some species use their anal fins as
gonopodium for the same purpose
Large, crescent shaped on the ventral side of the head
Variable shape and size at the tip or terminal part of the head
Hyostylic and autostylic
Usually five pairs of gill slits which are not protected by an
Five pairs of gill slits protected by an operculum (a lateral flap of
Type of gills
Larnellibranch with long interbranchial septum
Filiform with reduced interbranchial septum
The first gill slit usually becomes spiracles opening behind the eyes.
Afferent branchial vessels
Five pairs from ventral aorta to gills
Only four pairs
Efferent branchial vessels
Present in heart
A true cloaca is present only in cartilaginous fishes and lobe-finned
In most bony fishes, the cloaca is absent, and the anus, urinary and
genital apertures open separately 
Shape variable. Absent in some.
Short with spiral valve in lumen
Long with no spiral valve
Usually has two lobes
Usually has three lobes
Has large olfactory lobes and cerebrum with small optic lobes and
Has small olfactory lobes and cerebrum and large optic lobes and
Present in brain
Opens on top of head
Does not open to exterior
Most fish have double cones, a pair of cone cells joined to each
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
Ampullae of Lorenzini
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
Ovoviviparous types develop internally.
Oviparous types develop
externally using egg cases
Normally develop externally without an egg case
Wikimedia Commons has media related to Osteichthyes.
Wikispecies has information related to Osteichthyes
Ostracoderm - armoured jawless fish.
Bony fishes SeaWorld. Retrieved 2 February 2013.
^ Jaws, Teeth of Earliest Bony
^ Betancur-R, Ricardo; et al. (2013). "The Tree of Life and a New
Classification of Bony Fishes". PLOS Currents Tree of Life (Edition
Archived from the original on 2013-10-13.
palaeoblog.blogspot.com. Retrieved 2014-01-25.
^ "Descubrimiento de fósil de pez óseo en China aporta nuevos
conocimientos clave sobre origen de los
vertebrados_Spanish.china.org.cn". spanish.china.org.cn. Retrieved
^ Zhu, M; Zhao, W; Jia, L; Lu, J; Qiao, T; Qu, Q (2009). "The oldest
articulated osteichthyan reveals mosaic gnathostome characters".
Nature. 458: 469–474. doi:10.1038/nature07855.
^ Coates, M.I. (2009). "Palaeontology: Beyond the Age of Fishes".
Nature. 458: 413–414. doi:10.1038/458413a. PMID 19325614.
^ Post details: Critical transitions in fish evolution lack fossil
documentation Archived 2013-05-12 at the Wayback Machine. Science
Literature, 27 March 2009.
^ Pharyngula Archived 2012-03-09 at the Wayback Machine.Science blogs,
1 April 2009.
^ Clack, Jennifer A. (27 June 2012). Gaining Ground, Second Edition:
The Origin and Evolution of Tetrapods. Indiana University Press.
p. 23. ISBN 0-253-00537-X. Retrieved 12 May 2015.
^ Laurin, Michel (2 November 2010). How Vertebrates Left the Water.
University of California Press. p. 38.
ISBN 978-0-520-94798-6. Retrieved 14 May 2015.
^ Benton, Michael (4 August 2014).
Vertebrate Palaeontology. Wiley.
p. 281. ISBN 978-1-118-40764-6. Retrieved 22 May 2015.
^ Parsons, Alfred Sherwood Romer, Thomas S. (1986). The vertebrate
body (6th ed.). Philadelphia: Saunders College Pub.
^ Clack, J. A. (2002) Gaining Ground. Indiana University
^ Betancur-R; et al. (2013). "The Tree of Life and a New
Classification of Bony Fishes". PLOS Currents Tree of Life (Edition
Archived from the original on 2013-10-13.
^ Betancur-R; et al. (2013). "Complete tree classification
(supplemental figure)" (PDF). PLOS Currents Tree of Life (Edition 1).
Archived from the original (PDF) on 2013-10-21.
^ Betancur-R; et al. (2013). "Appendix 2 – Revised Classification
for Bony Fishes" (PDF). PLOS Currents Tree of Life (Edition 1).
^ Ricardo Betancur-R; Edward O. Wiley; Gloria Arratia; Arturo Acero;
Nicolas Bailly; Masaki Miya; Guillaume Lecointre; Guillermo Ortí
(2017). "Phylogenetic classification of bony fishes". BMC Evolutionary
Biology. 17: 162. doi:10.1186/s12862-017-0958-3.
^ Helfman 1997.
^ 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..."
^ Fritsches, K.A., Brill, R.W., and Warrant, E.J. 2005. Warm Eyes
Provide Superior Vision in Swordfishes. Archived 2006-07-09 at the
Wayback Machine. Current Biology 15: 55−58
^ Hopkin, M. (2005).
Swordfish heat their eyes for better vision.
Nature, 10 January 2005
^ Sepulveda, C.A.; Dickson, K.A.; Bernal, D.; Graham, J.B. (1 July
2008). "Elevated red myotomal muscle temperatures in the most basal
tuna species, Allothunnus fallai" (PDF). Journal of
Fish Biology. 73
(1): 241–249. doi:10.1111/j.1095-8649.2008.01931.x. Archived from
the original (PDF) on February 7, 2013. Retrieved 2 November
^ "Tuna — Biology Of Tuna". Retrieved September 12, 2009.
^ "Mola (Sunfish)". National Geographic. Retrieved 28 October
^ Based on: Kotpal R. L. (2010) Modern Text Book Of Zoology
Vertebrates Archived 2016-04-22 at the Wayback Machine. Pages 193.
Rastogi Publications. ISBN 9788171338917.
^ Romer, Alfred Sherwood; Parsons, Thomas S. (1977). The Vertebrate
Body. Philadelphia, PA: Holt-Saunders International.
pp. 396–399. ISBN 0-03-910284-X.
^ Schwab, IR; Hart, N (2006). "More than black and white". British
Journal of Ophthalmology. 90 (4): 406. doi:10.1136/bjo.2005.085571.
PMC 1857009 . PMID 16572506.
Helfman, G.S.; Facey, D.E (1997). "The Diversity of Fishes". Blackwell
Extant chordate classes
Ascidiacea (sea squirts)
Thaliacea (pyrosomes, salps, doliolids)
(Vertebrates + Myxini)
(fish + Tetrapods)
Agnatha (jawless fish)
Chondrichthyes (cartilaginous fish: sharks, rays, chimaeras)
Actinopterygii (ray-finned fish)
Squamata (scaled reptiles)²
¹subclasses of Sarcopterygii
²orders of class Reptilia (reptiles)
³traditionally placed in Anapsida
italic are paraphyletic groups
Evolution of fish
Lists of prehistoric fish
List of transitional fossils