Osteichthyes (/ˌɒstiːˈɪkθiːz/ ost-ee-IK-theez; from Ancient Greek ὀστέον (ostéon) 'bone' and ἰχθύς (ikhthús) 'fish'),[2] also known as osteichthyans or commonly referred to as the bony fish, is a diverse superclass of vertebrate animals that have endoskeletons primarily composed of bone tissue.

The vast majority of extant fish are members of Osteichthyes, being an extremely diverse and abundant group consisting of 45 orders, over 435 families and 28,000 species.

[5] However, since 2013 widely cited ichthyology papers have been published with phylogenetic trees that treat the Osteichthyes as a clade including tetrapods.

[6][7][8][5] Bony fish are characterized by a relatively stable pattern of cranial bones, rooted, medial insertion of mandibular muscle in the lower jaw.

Early bony fish had simple respiratory diverticula (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 swim bladders, the changing sizes of which help to alter the body's specific density and buoyancy.

In elpistostegalians, a crown group of lobe-finned fish that gave rise to the land-dwelling tetrapods, these respiratory diverticula became further specialized for obligated air breathing and evolved into the modern amphibian, reptilian, avian and mammalian lungs.

[12] Under this classification system, Osteichthyes was considered paraphyletic with regard to land vertebrates, as the common ancestor of all osteichthyans includes tetrapods amongst its descendants.

While the largest subclass, Actinopterygii (ray-finned fish), is monophyletic, with the inclusion of the smaller sub-class Sarcopterygii, Osteichthyes was regarded as paraphyletic.

[17] Coelacanthiformes Ceratodontiformes Tetrapoda Polypteriformes Acipenseriformes Lepisosteiformes Amiiformes Elopiformes Albuliformes Notacanthiformes Anguilliformes Osteoglossiformes Hiodontiformes Clupeiformes Alepocephaliformes Gonorynchiformes Cypriniformes Characiformes Gymnotiformes Siluriformes Lepidogalaxiiformes Argentiniformes Galaxiiformes Salmoniformes Esociformes Osmeriformes Stomiatiformes Neoteleostei All bony fish possess gills.

Bony fish can be any type of heterotroph: numerous species of omnivore, carnivore, herbivore, filter-feeder, detritivore, or hematophage are documented.