Many people fear sharks. But most sharks are harmless. In fact, the biggest sharks of all, the whale shark and the basking shark, eat only small fish and plankton.
Great white sharks and tiger sharks are more dangerous. They eat almost anything, from rubbish to big fish, seals, and sea turtles. Another dangerous shark is the hammerhead. It has a wide head shaped like a hammer, with an eye at each end. These sharks have been known to attack people.
Sharks are different from most other fish in several ways. Their skeletons are made of a tough, rubbery substance called cartilage, not bone. And the scales of sharks are not smooth like those of other fish. They are like millions of tiny, rough teeth that protect the animal. Shark’s gills are open, not covered like those of other fish. They look like slits on each side of the shark’s body. Sharks don’t have an air bladder like other fish, either. Instead, their livers are filled with oil, which is lighter than water. Also, gulping air helps them stay afloat. Even so, if a shark stops swimming, it will sink!
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