Breeding Daphnia

Author: Caryl Simpson
First published in Aquarium World August 2006

Despite being commonly known as water fleas, daphnia are not fleas – or insects for that matter. They are crustaceans. Less than 3mm, they are the most common crustacean found in lakes, ponds and small streams. An important part of the food chain, daphnia harvest algae cells that convert sun energy into food then pass this energy on to other animals, like fish.

Daphnia swim in a jerky manner by thrusting their powerful 2nd antennae forwards. This moves it towards the surface. It then pauses for a short while before the next stroke, slowly falling downwards again before the next stroke propels it forward again.

Breeding your own daphnia outside is a great way to get good, free food for your fishes. They are also good for clearing green water (but only if no fish are present as they will eat the daphnia before the daphnia get the chance to eat the algae).

Finding live cultures can be difficult so try to find an aquarist with a culture they are willing to share. I have found daphnia do not travel well, probably due to lack of oxygen. Visit a nearby farm and look in stock troughs, always a good source of daphnia. Watch you don’t get parasites, predators, or other nasties in with them too like blanket weed.

You will need a container in which they can breed. I use fibreglass ponds, a bath, and half a mussel float for mine. Larger containers are better as they keep a more constant temperature in summer. A good surface area is ideal as daphnia, although not demanding, appreciate a good oxygen supply. I am lucky where I live as I just fill my container with water and wait. The daphnia seem to find their own way into the container, along with other creatures like mosquito larvae.

Once you have your container, fill it with green water and add the daphnia. They will live and breed in this. You will find the water clears very quickly as the daphnia feast on the algae so you will need to feed the daphnia to keep them alive and breeding in large enough numbers to feed regularly to your fish. Green water and activated yeast are the best foods. About 5g of yeast per 10 litres every 5 days is sufficient.

Bacteria found in dried sheep, horse or cow dung is another food source. Put it in a nylon bag and hang in the container. The water will turn cloudy after a time which is the bacteria multiplying. A fast way to culture bacteria is to throw in some trout pellets or dog biscuits.

Other foods suggested are dried blood, blood meal, bran, wheat flour and sweet potato baby food mix. Try them out and see which suits you best. DO NOT OVERFEED, it will just foul the water. Experiment as amounts vary depending on the size of the container and the number of daphnia present.

To harvest the daphnia, and it is important to do this at least once a week to keep numbers in check, catch them with a fine net.

Make sure pesticides are not used anywhere your daphnia containers.

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