Daphnia is also known as “water bugs” or “water fleas” due to their jerky motion. They live in freshwater and are really easy to cultivate at home. Daphnia can be used regularly to provide your fish with more variation, or seasonally to induce breeding. It can also be used as fry food for bigger fish. Unlike uneaten dried or frozen food, Daphnia will not foul the water – they will stay alive in the aquarium until the fish decides to eat them. Cultivating Daphnia at home is economical and will provide you with a constant source of disease-free live food.
To start your own Daphnia culture you need to buy a starter culture from your local fish store. If your LFS do not have any Daphnia, contact your nearest aquarium club, somebody will probably be willing to sell or donate a started culture to you.
Place the container that you plan to use for cultivating Daphnia in a light spot, because Daphnia are more active when it is light. Artificial light works just as well as sun light, so you can for instance place them under a lamp in your basement. Add water to a container and pour in your Daphnia culture. Add a slow bubbling air stone to keep the water from becoming stagnant and oxygen depleted. Keep the water temperature around 72-75 degrees F.
Mixing one package of dry yeast with one cup of soy flour will provide you with a great source of food for your Daphnia. Stir 1/8-1/4 teaspoon of this mixture into a cup of warm water and pour it into your Daphnia container. This will cloud the water and there is no need to feed your Daphnia again until they have filtered out and consumed all the yeast-flour (i.e. when the water has become clear again). Avoid over-feeding, since this will cause the water to go foul and kill the Daphnia.
You should ideally avoid using a filter in your Daphnia container because a filter will catch a lot of tiny life forms that the Daphnia likes to feast on. Regular water changes are a better way of keeping the water quality up. You can combine water changes with harvesting by using a siphon to suck up a part of the water and filter it through a shrimp net. The removed water can then be replaced with new, fresh water and the shrimp net will be filled with Daphnia for your fish. You will also need to remove mulm from the bottom of the container every other week.
If you keep small fish and big fish in separate aquariums, you can use fish nets to size your Daphnia accordingly. This way, you will have big Daphnia for your big fishes, small Daphnia for small fishes and tiny Daphnia for fry aquariums.