Daphnia, small planktonic crustaceans sometimes called "water bugs," are at the base of many fresh water food webs and are commonly consumed by small fish. They are also eaten by many aquarium fish and pet fish.
Some fish of economic importance, including young Sockeye salmon and perch, eat them too. They are very nutritious as they are high in protein and vitamins A and D. Their use as fish food, whether live or in dehydrated flakes, is widespread, particularly for tropical pet fish. As they are zooplankton, they are also eaten by filter feeders, such as larger crustaceans, and invertebrate predators little bigger than the daphnia themselves.