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.
Large species may eat seals, turtles and penguins. Some sharks, like the whale shark feed on plankton. Blue sharks swim in leisurely circles when they are hungry and become increasingly excited when they sense food. Most fish lay eggs in the water which are then fertilised by the male. But shark eggs are fertilized inside the female's body.