Sharks are fish with replaceable teeth. Sharks include species ranging from the hand-sized pygmy shark, a deep sea species that is only nine inches in length, to the whale shark, the largest fish, which grows to a length of approximately 39 feet.

Sense of Smell:
Sharks have an amazing sense of smell, with some species able to detect as little as one part per million of blood in seawater, up to a quarter of a mile away. They are attracted to the chemicals found in the guts of many species, and as a result often linger near or in sewage outfalls. Some species, such as nurse sharks, have external barbels that greatly increase their ability to sense prey.

Sense of Sight:
Sharks have eyelids, but they do not blink because the surrounding water cleans their eyes. To protect their eyes some have membranes, which cover the eyes during predation, and when the shark is being attacked. However, some species, including the great white shark, do not have this membrane, but instead roll their eyes backwards to protect them when striking prey.

Sense of Hearing:
Sharks also have a sharp sense of hearing and can hear prey many miles away. A small opening on each side of their heads leads directly into the inner ear through a thin channel.