Artemia

Artemia, or brineshrimp, are a good source of food for many fish and can be bought live, freeze dried, or frozen (frozen is often preferable as you get more for your money). Brineshrimp can also be raised artificially by purchasing the eggs and adding them to oxygenated saltwater at the right temperature.

Due to the tough nature of brineshrimp, hatching and raising is easy to do and can be a very cost effective (and interesting) way of providing food for your fish. It is so easy to do this that Artemia eggs are often sold, along with hatching kits as 'sea monkeys' for children.