Daphnia are a small freshwater crusteans are found most places in the world. They are an easy to raise as a live food for fish. There are two species that are mainly used for tropical fish. The larger one is Daphnia magnus. It is about 1/5 of an inch long and a pinkish color. The other species is D. pullex which is smaller and either whitish or clear.  In both species the females give birth to about fifteen babies every three days. This is in ideal conditions. The babies grown and start producing babies in a few days. All  Daphnia are females except during special circumstances. Just before a tank crashes a few male are born and the females will produces cysts or eggs. You can go from a few to a tank full in less than a month. The other species is D. pulex which is about 1/4 the size and a clear or white color.  It reproduces at a similar rate. It is easier for smaller fry to eat. You must be careful with the amount of Daphinia that you feed to fish. The shells of the bodies can give the fish digestion problems if given too regularly. They should be fed to fish only once or twice a week.

Daphnia are filter feeders. They are constantly straining the micro-organism from the water. They live off bacteria, algae and other small animals. The easiest source of food is green water. You can either buy green water or start your own. Place a pea in a quart of water. It will turn green as the algae absorb the nutrients from the decaying pea. When the water has turned a nice cloudy green color. You can add some to a ten gallon fish tank. You can add lettuce leaves or pea to fertilize this tank. When the water has become so green that you can see through it to can add a few Daphnia. I had three tank going this way using a flourescent light turned 24 hours a day. There are two ways to keep the tanks going. I have used old aquarium water. This fed the green water. Some sources state that you must use clean spring water. You can buy some cheap at your local grocery store. Daphnia are very sensitive to pollution in water. They are used to test the toxicity of water by environmental labs all over the country. If you try using your tap water and they all die you know something is wrong with your water.

After you add the Daphnia there will be a population explosion in your tank. In a short time the water will become clear. You can start harvesting your Daphnia with a shrimp net. When you dump them in your tanks the fish will usually eat them all in minutes. The Daphnia population will approximately quadruple every day. You can harvest every day for some time. You will need to do partial water changes to keep the water from getting too dirty. At some point the population will crash. This is the reason to have three tanks going when one crashes another one will be coming online to do the work. Share these with your friend so if you lose them all  you can always get more. I went for a year and half once I figured out how to keep them alive.

search for daphnia
look in the pet supplies catagory
search for green water.