Scientists classify about 360 species of fish as sharks. These fish live in oceans throughout the world but are most common in warm seas. Sharks vary greatly in size and habits. Some kinds of sharks live in the depths of the ocean. Others are found near the surface.
Some species of sharks live in coastal waters, but others dwell far out at sea.
A few species enter rivers and lakes that have outlets to the sea. Scientists believe that one species, the Ganges River shark of India and Pakistan, lives only in rivers. Most of them eat live fish, including other sharks. In fact, a shark's most common natural enemy is a larger shark. Most sharks eat their prey whole, or they tear off large chunks of flesh.