Mammals nurse their young. A mother whale's milk is rich in fat, so the calves develop a thick layer of blubber. Mammals breathe air. Whales breathe air through nostrils called a blowhole, located on top of the whale's head. When it needs oxygen, a whale surfaces, thrusts its blowhole clear of the water, exhales, and takes a deep breath of air into its lungs.
Mammals have hair.
Although adult whales rarely have hair, young whales may have sparse hairs along the rostrum. Although whales five in the sea and have a body shape similar to fish, whales are not fish. Fish take oxygen from the water with gills. Fish have scales. Fish are cold-blooded.