Why do sharks sink when they don't move in water?

Fish are divided into two as boned and cartilaginous. Sharks and stingrays are cartilaginous fish. These are non-bony fish olds. One of the differences between them is the so-called swim bladder. Boned fish have a gas-filled swimming pouch. This structure allows the fish to stop without moving in the water. Cartilage fish have no swimming pouch. Another difference is the structure of the gills. Although the muscles around the gills of the sharks are active, they are not strong enough to pump water. For these reasons, sharks have to swim constantly.