Any fish of the class Osteichthyes (Teleostei or bony fish), the largest group of fishes. They have an ossified or bony skeleton and well developed jaws, usually bearing teeth. There is a single gill opening on both sides, covered by a complex of bones forming the operculum or gill cover. The skin is covered by partly embedded bony plates, the scales, which are thought to have formed during evolution when fishes spread out into freshwater. Ordinarily a gas bladder is present. These fishes usually have external fertilization and are, with a few exceptions, oviparous.