Daphnia are an excellent addition to your fish’s diet. They are packed with protein and are particularly good for getting fish into breeding condition.
They’re also a popular food for fish fry as they grow.
You can buy frozen or freeze dried Daphnia, but the most nutritious are fresh, live ones.
Luckily, they’re not hard to culture. Today, I’ll go over what you need to know to raise your own Daphnia to feed to your fish.
What are Daphnia?
Daphnia is a genus of tiny freshwater crustaceans, also known as common water fleas. There are over 200 species of Daphnia, but the most common are Daphnia pulex and Daphnia magna.
These little critters are less than ½ inch (1.25 centimeters) long. They have large, round eyes and a pointed mouth that looks almost like a short beak. Their bodies are shaped like an oval that’s pointed on one end.
5-6 pairs of legs jut from beside their heads. They flail these around to propel themselves through the water.
The jumpy, jerky motion of their swimming resembles the movement of terrestrial fleas, hence their common name.
Daphnia are filter feeders. As they swim through the water column, they siphon water through their mouths straining out bacteria, algae and other detritus that they consume as food.
How to Culture Daphnia
It’s a good idea to start more than one Daphnia culture. Even experienced aquarists have had cultures get out of balance and suddenly crash, causing a mass die off. Having a backup can be helpful.
Equipment
Container
You can culture Daphnia in something as small as a 5 gallon (19 liter) bucket, but the larger the container is, the more stable the water parameters will be.
For a total novice, a 10 gallon (39 liter) container or larger would be best. It can be an aquarium, a plastic tote or a large bucket. It doesn’t need to be super fancy.
Heater
As long as you are keeping your culture indoors, you really shouldn’t need a heater.
They’ll do fine at room temperatures between 60°-80°F (16°-27°C).
Filtration
OK this is a matter of some debate.
Yes, technically, you don’t have to filter your Daphnia colony. But, this does mean that you will have to dedicate more time to water changes especially as the population grows.
I would recommend using a small, seasoned sponge filter in your Daphnia cultures.
Just like fish or shrimp, Daphnia produce waste that can cause a buildup of toxic substances, like ammonia and/or nitrite.
The beneficial bacteria in a sponge filter can help process those wastes and lessen the need for water changes.
Light
Daphnia are attracted to light. You don’t necessarily need to add a light to a Daphnia culture, but they shouldn’t be in darkness all the time either.
Make sure the culture is getting at least ambient light throughout the day.
Plants and Decor
Daphnia don’t absolutely require plants and decor, but plants like duckweed and frogbit, can help keep your water cleaner. Plus, Daphnia will eat any infusoria that grows on them.
Make sure that you dechlorinate all water for your Daphnia culture. Chlorine/chloramine will kill Daphnia.
Starter Culture
Once you’ve got your tank all set up, it’s time to add some Daphnia to get your culture going.
You can try to collect some from a local pond, but this can be hit or miss, especially in the middle of winter or during a hot summer.
Also, you can inadvertently bring in other critters that you don’t want, like hydra, planaria, damselfly larvae or anchor worms.
I think it’s a safer bet to order a starter culture from a reliable source.
You might be able to get some Daphnia from a local aquarist, or you can order some.
If I’m going to order a live product like this, I like to use Carolina Biological Supply Company. They’re pretty much the gold standard for the industry.
They supply labs and schools throughout the country and have rigorous quality controls in place.
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Feeding Daphnia
Daphnia need tiny food that can float in the water column. The most popular things to feed them are:
- Yeast
- Spirulina powder
- Pea powder
- Soy flour
I personally would use a mix of yeast and spirulina. Both yeast and spirulina are great sources of protein and the spirulina contains a wide variety of vitamins.
The more nutrient-rich the Daphnia’s food is, the more nutritious they will be for your fish.
You can mix up a 50/50 mix of dry yeast and spirulina powder.
Then, mix a ¼ to ½ teaspoon of the powder with a cup of water.
Drip this mixture over the surface of the water in your Daphnia culture until the water becomes cloudy.
How Often to Feed
Feeding a Daphnia culture is probably the biggest pitfall that aquarists run into.
Too little food and your Daphnia could starve to death.
Too much food and it can foul the water, killing your culture.
How often you feed your Daphnia will change based on the size of the culture.
The water should be fairly cloudy when food is added to the tank. You don’t want to add more food until the water starts to clear up again.
If there isn’t much water flow in your Daphnia tank, you should stir the water up every day. Stirring will kick up any food that has sunk to the bottom, suspending it in the water column again, where Daphnia can access it.
Once the water starts to clear up again, it’s time to put in some more food.
Water Changes
Daphnia excrete waste, just like any other animal. Even if you have a sponge filter running in the tank, nitrate will still build up and need to be removed.
Cultures usually need 25% water changes twice a week.
You can do this one of two ways:
- Put a screen over the intake for your siphon to prevent them getting sucked up
- Strain daphnia out of water coming out of the siphon with something like a brine shrimp net
It’s up to you to figure out which one will be easier for you and your setup.
Just make absolutely sure to dechlorinate your replacement water.
Harvesting Daphnia
This part is really simple. You can just swirl a brine shrimp net in the Daphnia tank to scoop some out.
You can then just place the net in the tank with your fish.
Or, if you have multiple tanks to feed. You can suck up Daphnia with turkey baster and dole them out to your tanks.
Final Thoughts
Daphnia are a very nutritious addition to your fish’s diet. They have a very high protein content that’s especially great if you’re trying to get fish conditioned for spawning.
They’re not hard to culture, they just require some care and attention.
You can raise them in something as simple as a large bucket with a little sponge filter. There’s no need for an elaborate setup or expensive equipment.
I hope you find this article helpful.
I wish you and your fish the very best!
