Daphnia (Water Fleas)

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Despite being a staple in aquaculture (especially in the far east), Daphnia has begun to make strides here in the U.S. only in recent times. Even so it is not as widely used in commercial aquaculture here as much as back in the far east. This is probably partially due to its relatively low nutritional value compared to the easily available commercially produced foods here. But still, for the small time hobbyist, it is a relatively easy live food to culture and is useful for an occasional treat and EXTREMELY useful in getting wild caught fish and fish that have gone off their feed to start eating again. Their jerking motion triggers a predatory strike in even the most finicky fish. Their tolerance to a variety of harsh water conditions make daphnia one of the easier live foods for the hobbyist to culture. In the words of a fish farmer in Singapore (translated from the local dialect "Hokkien") "If you cannot keep daphnia alive... I won't even trust you with my pet rock!"

There are several species of daphnia, of which Daphnia Magna and Daphnia Pulex are the most readily available to hobbyist. Also readily available is Moina, which is a cousin of Daphnia. All three will be collectively referred to as "Daphnia" in this article. Of the three, Magna being the largest size with females growing to 3 - 5 mm, Pulex being the medium sized with females ranging from 2.5 - 3.5 mm. Moina are smaller or comparable to Pulex with females growing to 1 - 1.5 mm. Males of these species are generally smaller than females.

Obviously you want to culture larger species for larger fish and smaller species for smaller fish.

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Culturing

Daphnia is fairly simple to culture. They may be cultured in anything from 1 gal jars to 55 gal drums. They can tolerate a wide range of temperatures. They can even sit outside or in the garage during winter as long as the water doesn't freeze over. I have them in a 10 gal aquarium sitting outside in the Texas sun so I know that they can take fairly high temps also. For Magna, i find that to reach an acceptable population density to be able to harvest regularly, that they should be cultured in at least a 10 gal aquarium. Pulex and Moina may be cultured easily in 2-1/2 gal aquariums or mason jars. Or if you have some space and you want a really low maintenance culture, just fill an old plastic wading (baby) pool and leave it out where it gets direct sunlight. As soon as the water turns green, seed the culture with daphnia and just leave it alone.

Although it is not absolutely required that you provide agitation to the water, but i find that some agitation helps keep the food in suspension and also helps aerate the water a little bit more. This is usually easily done using a rigid airline tubing and a steady stream of air. The water should not be turbulent such that the poor daphnia are being tumbled too aggressively. Just enough air to move the water around. No filtration is needed.

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Feeding

By far the cheapest and most easily obtainable food for daphnia is greenwater (freshwater microalgae). To grow greenwater you can either do purposeful culturing with the same method as culturing saltwater microalgae, or simply set a bucket, wading pool or aquarium of water out in the sun, add some grass clippings, pond water or even old aquarium water and just leave it alone. Or better still, If you have a friend that is struggling with greenwater problems in his aquarium, you can ask him for some water to seed your culture. He'll look at you weird but just smile back at him an thank him.

When the water is nice and green, you can use some of it to "feed" your daphnia. Just add enough green water such that the daphnia's water has a nice green tint to it. Feed them again when the water turns clear.

The other (not so free but still pretty cheap) method is to feed them activated yeast. Simply head over to your local big box grocery store and buy a jar of activated dry yeast. I prefer the jars over the pre-portioned packets because I almost never use the entire packet for a single feeding. Which pretty much means I have an opened packets of yeast sitting in my fridge. With a screw top jar, i can store the entire jar in the fridge and simply remove portions as I use them.

Dissolve a pinch (or spoon full if you have lots of mouths to feed) of yeast in some water such that you get a cloudy yeast suspension. Feed enough of this suspension to the daphnia such that the water is only just cloudy. Feed again when the water once again becomes clear.

Here's a vid of my 2-1/2 gal daphnia culture and feeding them:

Water Quality / Harvesting

Although daphnia are quite tolerant of bad water conditions, they still appreciate water changes. If you have your culture aquarium / bucket / pool outside and exposed to the rain, then you probably won't have to worry too much about WC's. But if you culture them in little jars, you might have to keep up those water changes. When water quality deteriorates to a point where the daphnia becomes stressed, they'll start producing ephippia or resting "eggs". You will notice little black "egg sacs" either on the bottom of the jar or that they have black "tumors" growing in their bellies. This is your signal that they don't like the water and they are producing dormant eggs that will hatch again when the rainy season comes along bringing fresh water.

The method i use to keep the water in the jars fresh is simply every time i harvest the daphnia, I either scoop a large cup or siphon the water out of the culture aquarium and into a brine shrimp net or rotifer sieve. The water that passes through the net gets dumped and the contents of the net go to feeding the fish. Then simply top up the water in the daphnia jar with dechlorinated aged tapwater.

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Plug

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