But in truth a shark can be one of over 370 different types and range in size from the whale shark, the largest of all fish that measure up to forty feet long, to the smallest shark, the spined pygmy shark that only grow to a length of about six inches. Harder - Sharks are found in all types of oceans including the arctic, but most are found in warm seas. Some prefer the spacious ocean depths, others are found in coastal waters, a few enter rivers and lakes that empty into the sea, and one species found in India and Pakistan lives only in freshwater rivers. Sharks are different from most other kinds of fish. They have a unique boneless skeleton that is composed of tough, elastic cartilage.
Most sharks have a rounded tough-skinned, streamlined shaped body, somewhat like a torpedo.
This helps them to swim. Unlike most fish, sharks do not have a swim bladder. Instead their oversized liver is filled with an oil that is lighter-weight than water. This also aids their swimming ability. Even so, most sharks must constantly swim or their body would sink.