Learn a lot about water life and water by growing Daphnia.

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If you want something to keep you amused for a long time try breeding Daphnia. They are also known as water fleas but they are not fleas! They are Cladocerans a type of crustacean. I grow them in my lab because every now and again someone wants to know if their water is OK to drink. I figure that if the Daphnia survive then it must be OK because Daphnia are the proverbial 'canary in a coal mine'. Because they are usually found mainly in clean water it is assumed that they don't like chemicals or pollutants.

Where to find them: Look in any fresh water dam or creek. Daphnia can be picked out easily because they move reasonably quickly, sometime with jerky movements but sometimes with quick smooth movements. There are a few different species and some Cladocerans that are closely related to Daphnia are worth collecting as well.

Daphnia with eggs

Daphnia with eggs. I think this is Daphnia carinata.

Housing: They do well in a tallish container like a plastic bottle with the neck cut off. Put a little soil or old compost in the bottom. The soil adds a few plant nutrients, salts and food for the daphnia. Then put in some tap water that has no Chlorine (let it stand for a day or so) or use clean creek water. The Daphnia will grow to about 3 mm. Every now and again top up their water with some fresh water. If they start to multiply well put a few into a new container. It is better to use several smaller containers so you won't lose the lot if something goes wrong.

Feeding: Feed then yeast or single celled algae or a little left over liquid from some vegetable soup. Make up the yeast by adding a little dry or frozen yeast to some warm water with a little sugar. Let the yeast multiply for a few hours then feed a little to the Daphnia. They also might like some single celled algae that often thrive in containers left outside. If the daphnia are feeding you should notice some darker colouring through the length of their gut. Because they need Calcium to build their shells, add a little crushed eggshell to the water.

Observing: Get out a magnifying glass and have a close look. They have a shell (carapace) with two sides and open at the bottom. You should see the front legs with very fine bristles that sweep the food towards the daphnia's mouth. They have an eye spot and gills always moving underneath the carapace.

Daphnia with live young.

Breeding: Most of the time daphnia produce live young that are just miniatures of the adults. If there are young then you know they are thriving. Sometimes particularly if water quality decreases they make eggs that you will see under the carapace along the daphnia's back. They will shed these off and the eggs will rest on the bottom. The eggs are tough and hatch when conditions are favourable.

Handling: Daphnia can be moved using a large diameter tube with a bulb like a large dropper. Or, pour some water out through a fine strainer then tip them back into a new home. They have to be handled gently because they can get air under their shells and will then float.

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