Sharks are fish with a full cartilaginous skeleton and a streamlined body. They respire with the use of five to seven gill slits. Sharks have a covering of dermal denticles to protect their skin from damage and parasites and to improve fluid dynamics; they also have replaceable teeth. Sharks include species ranging from the hand-sized pygmy shark, a deep sea species of only 22 centimetres (9 in); in length, to the whale shark, the largest fish, which grows to a length of approximately 12 metres (39 ft); and which, like baleen whales, feeds only on plankton through filter feeding. The bull shark, is the best known of several species to swim in both salt and fresh water and in deltas.