The main taxonomic groups of fish, structural features and representatives.

The Pisces superclass is represented by 2 classes: Cartilaginous and Bone. The most common representatives of the Cartilaginous are sharks and rays. They do not have a swim bladder, their skeleton is cartilaginous, most are covered with scales with spines. The Bone class, in turn, is subdivided into bone-cartilaginous ones – they have a bone-cartilaginous skeleton, as well as a swim bladder, and they have gill covers (beluga, Russian sturgeon); lungs – have both gills and lungs (Australian horntooth); cartilaginous – have a paired lung, which is formed from a swim bladder and have a cartilaginous skeleton (coelacanth) and bony – have an ossified skeleton, a swim bladder, as well as bone scales (salmon, pink salmon).