Daphnia (daff-NEE-ah) are small freshwater crustaceans belonging to the order Cladocera and are found nearly everywhere in the world. They are an important food source for most aquatic insects, amphibians, birds, and of course, fish. High in protein and vitamins A and D, daphnia also have an exoskeleton composed of indigestable chitin (KITE-un), which aids in digestion. Aquarium fish that are offered live daphnia will display more vivid coloration and increased activity, and even notoriously finicky eaters like bettas find daphnia difficult to resist!

There are hundreds of species of daphnia in a wide variety of sizes, but the most important for the purposes of fish food culturing are the three most commonly available.

Daphnia magna: Excellent adult fish food. When most people think of daphnia, they think of Daphnia magna. D. magna are 2 to 5 mm in size.
Daphnia pulex: Probably the most widely distrubuted daphnid and also the most variable, ranging from 1.5 mm to 3.5 mm.
Moina: Closely related to daphnia, except they are much smaller in size (0.5 mm) and are fairly translucent.
Note: Adult D. magna or D. pulex can be used as automatic feeders in fry tanks. Simply place some daphnia in the fry tank; as new daphnia hatch out, they will feed the fry and as the fry grow out, they will eventually eat the adult daphnia.

Daphnids have a nearly bulletproof reproductive strategy. When condition ...

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