Sharks are fish. However, they do not have bones like other fish. Their skeleton is made of cartilage. This is the same bendable material that is in your ears!
They also do not have a swim bladder, the air filled balloon-like organ that keeps most fish upright.
Sharks have gill slits but no gill-cover, which is common to most bony fish. Because they have no swim bladder to keep them buoyant, sharks sink when not swimming. Shark's bodies are heavier than water and most sharks are constantly on the move. By moving forward with their mouths open,sharks move water across their gills for breathing. The larger species produce live young that arefully formed, miniature versions of their parents. Mother sharks offer no food or protection for theiryoung. Young sharks do have a fighting chance, though, as they are born with a full set of teeth and the ability to swim