Osteichthyes

Bony fish Temporal range: 420–0 Ma PreЄ Є O S D C P T J K Pg N
Atlantic herring
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
clade:	Craniata
Subphylum:	Vertebrata
Infraphylum:	Gnathostomata
Superclass*:	Osteichthyes Huxley, 1880
Classes
Actinopterygii Sarcopterygii

Osteichthyes ( /ˌɒstiːˈɪkθi.iːz/), also called bony fish, are a taxonomic group of fish that have bony, as opposed to cartilaginous, skeletons. The vast majority of fish are osteichthyes, which is an extremely diverse and abundant group consisting of over 29,000 species. It is the largest class of vertebrates in existence today. 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.^[1]

In most classification systems the Osteichthyes are paraphyletic with land vertebrates. That means that the nearest common ancestor of all Osteichthyes includes tetrapods amongst its descendants. Actinopterygii (ray-finned fish) are monophyletic, but the inclusion of Sarcopterygii in Osteichthyes causes Osteichthyes to be paraphyletic. Paradoxically, Sarcopterygii is considered monophyletic, as it includes tetrapods.

Most bony fish belong to the ray-finned fish (Actinopterygii); there are only eight living species of non-tetrapod lobe-finned fish (Sarcopterygii), including the lungfish and coelacanths.

Traditionally, the bony fish had been treated as a class within the vertebrates, with Actinopterygii and Sarcopterygii as subclasses. However, some recent works have elevated Osteichthyes to superclass, with Actinopterygii and Sarcopterygii as classes.^{[citation needed]}

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.^[2]

Osteichthyes are primatively ectothermic (cold blooded), meaning that their body temperature is dependent on that of the water. But some members of the family scombridae such as the swordfish and tuna have achieved various levels of endothermy. They can be any type of heterotroph: omnivore, carnivore, herbivore, or detritivore.

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 female.

Examples

The ocean sunfish is the largest 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 (5,080 lb). Other very large bony fish include the Atlantic blue marlin, some specimens of which have been recorded as in excess of 820 kilograms (1,800 lb), the black marlin, some sturgeon species, the giant grouper and the goliath grouper, both which can exceed 400 kilograms (880 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.

See also

• Ostracoderm - armoured jawless fishes.
• Acanthodians - relatives of the bony fishes
• Fish - fish
• Prehistoric fish

References

1. ^ Jaws, Teeth of Earliest Bony Fish Discovered
2. ^ Helfman G.S., B.B. Collette and D.E. Facey. The Diversity of Fishes. Blackwell Sciences, 1997