Sharks have five to seven gill slits located on each side of their heads. They use their gills to filter oxygen from the water and do not have gill covers.
There are more than 465 species of shark in the ocean. Their skeletons are made of cartilage, a tissue that is more flexible than bone. Sharks have many rows of teeth, and they grow new teeth to replace lost ones. They eat fish, crustaceans, mollusks, plankton, krill, marine mammals and other sharks. Sharks can detect blood in the water from miles away. They can live in various temperatures, and some species of shark can swim in salt, fresh and brackish waters.