Most fish breathe by drawing water over four or five pairs of gills that are located in chambers covered by a protective flap, the operculum. Some fish breathe air while a few may even absorb air through their skin if they lack scales. Reproduction Details in reproduction of bony fishes vary extensively. Most species are oviparous, reproducing by external fertilization after the female sheds large numbers of small eggs. However, internal fertilization and live birth characterize other species.
Some bony fishes display complex mating rituals.
The skin of bony fishes is often covered by flattened bony scales that differ in structure from the toothlike scales of sharks. Glands in the skin of a bony fish secrete a mucus that gives the animal its characteristic sliminess, an adaptation that reduces drag during swimming and acts as a barrier to infections. The Swim Bladder Another adaptation of most bony fishes not found in sharks is the swim bladder, an air sac that helps control the buoyancy of the fish. Bony fishes are generally maneuverable swimmers, their flexible fins better for steering and propulsion than the stiffer fins of sharks. Nearly all the families of fishes familiar to us are ray-fins.