Water flea is the common name of certain tiny animals that live primarily in freshwater ponds and lakes. A few species (kinds) of water fleas live in the ocean. Water fleas are a major source of food for many fish. Water fleas measure about 1/125 to 3/4 inch (0.2 to 18 millimeters) long. They received their name because their jerky swimming motions resemble the jumping of a flea. They swim by making a rowing movement with their antennae (feelers), which extend from the front of the head.
A water flea’s body is covered by a transparent carapace (shell). The action of the heart and other organs can be seen through the carapace. As a result, water fleas are often used in scientific experiments to observe the effects of drugs on body organs. The water flea’s head is not covered by the carapace. Water fleas use their four to six pairs of legs, called appendages, for filtering food particles from the water.
