Although sharks are boneless, they are still heavier than sea water and must swim to avoid sinking. Bony fish have air bladders to help make them buoyant. Sharks rely, instead, on enlarged livers. These livers are filled with as much as 18 gallons of an oil that is lighter than sea water. This along with their fins, gives them lift.

Sharks which range across the open seas have large livers compared with their body size. Bottom dwelling Sharks have smaller livers because they do not need to travel as far off the sea floor. The only shark that uses air for additional buoyancy is the sand shark which gulps air to allow it to hover. A swimming shark is very much like a well designed air craft in-flight. Coordinated movements of the dorsal and pectoral fins allow it to move smoothly. But because of their streamlining, sharks pectoral fins are less flexible and don’t rotate like those of a bony fish. Fish can reverse, and sharks can not.

Instead, the shark has to fall away from obstacles instead of just reversing. Sharks are infamous for their menacing front teeth. In actuality, little know that the sharks entire body is covered with teeth. How is that for a shock! They are called dermal-denticles or skin teeth. They are pointed backwards to smooth the flow of water over the body and reduce drag. This in turn helps to increase speed. It is however, the sharks tail that controls its speed, these tails are designed to suite the sharks way of life. Bottom dwelling sharks feed on slow moving prey, so their tails are designed to give them more stability rather than speed. In open water sharks the tails are designed for great burst of speed and power to catch fast moving prey.

One of the most powerful swimmers is the hammerhead. Located at each side of its anvil shaped head is an eye, a nostril, and sensory organs, which help them to steer, and to detect prey more easily.