Skeleton - a set of hard and cartilaginous formations in the body of fish, serving as a support for the body or its individual parts and protecting it from mechanical damage. There is a distinction between internal (supporting) and external (protective) skeleton. The internal skeleton consists of the axial skeleton (spine), the skeleton of the head (skull and visceral apparatus), the skeleton of the thoracic (shoulder) and abdominal (pelvic) belts and the skeleton of the fins (paired and unpaired). The internal skeleton in cartilaginous fish (sharks, rays) is cartilaginous for life, in bony fish - bony. In roundheads, sturgeons, bipedal fish, the main supporting element is the chorda, preserved in them for life, in all other fish it is replaced by a bony spine consisting of vertebrae. The external skeleton is placoid scales of sharks, ganoid scales of multipers and panfish.