The most popular and desirable of live foods for aquarium fishes is Daphnia. this generic name includes several species, the most common of which are D.pulex, D. longispina, and D. magna. this listing is according to their size, an important factor when baby fishes must be fed. All species breed in the same manner and require the same general care.

Raising Daphnia is a simple matter if their life cycle and requirements are completely understood. Sex in the Daphnia is rather easily ascertained as the female carries eggs in a brood sac. These eggs appear as tiny dark spots when the animal is held in a small glass container and light is allowed to pass through it. Initial cultures should have a dozen pairs as a starter, at least. Experience has shown that a culture will reach its peak of productivity about 3 weeks after the culture has been initiated.

Outside cultivation of Daphnia is much easier. Pools should be fertilized with sheep, cow, or horse manure. A week or so later some Daphnia should be introduced. If the pool does not freeze, the culture should be available all year round. Frequent addition of lettuce leaves is helpful. Earth-bottom pools or all-concrete pools are used to equal advantage. the parasite problem is manifest in the outdoor situation.

(source from: http://www.brooklands.co.nz/wardley/wgold.htm)