Like other Cladocerans, Daphnia are an important link in the food chain. Most species of Daphnia are found in freshwater habitats, but a few occur in marine environments. The microscopic organisms feed upon the microscopic particles and phytoplankton they encounter in their aquatic surroundings. In turn, Daphnia act as food for juvenile fish. These tiny crustaceans are one of the most popular live food for aquarium fishes, but are also important on a much grander scale. In the Great Lakes of North America, water fleas are the basic food of nearly all commercial fish species.