Water fleas live in stationary freshwater regions. They have a strong sense of smell via their special antennae. For example, they can even smell where their enemies are hiding. They are born with two eyes which later fuse together into one eye. Water fleas are eaten by many animals, such as fish and aquatic insects. Because there are so many of them, they form an important source of food. Water fleas are not found in the sea. Other small crustaceans serve as an important source of food there, such as the copepod.