Hopefully you already know that dolphins are not fish. Dolphins are warm blooded mammals like us. They breath air through a nostril on the top of their heads called a blowhole. Because dolphins breath air, they must surface periodically. Fish, however, breath by using gills underwater, and therefore do not need to surface. Many fish also have scales, which dolphins do not have. Instead, the skin of a dolphin feels rubbery. A layer of fat, called blubber, under their skin keeps them warm. The locomotion of fish and dolphins is also different. Fish swim by moving their tails from side to side (horizontally). However, dolphins swim by moving their tails up and down (vertically).