Most sharks have their mouths on the underside of the head. The mouth has rows of sharp teeth that are replaced as they wear out. Sharks vary greatly in size and habit. Whale sharks are the largest of all fish and can grow up to 12 m long and weigh up to 14 tons. The smallest sharks are the tiny pygmy sharks which are fully grown at 25 cm long.
Sharks have a skeleton made up of a tough, elastic substance called cartilage.
Some sharks can swim very fast. They have a highly developed sense of smell, hearing and sight. They can scent their prey in the water from a great distance. Their sensitive eyes can see clearly even in the dim light of the ocean depths. Sharks are carnivorous and eat fish, including other sharks.