Culturing Daphnia for Tropical Fish and other Critters
Daphnia can be a great food for may species of fish and small aquatic critters. They are relatively easy to culture if you know a few things about them. Their cultures tend to crash when the water temperatures go outside of a certain range and the water quality declines too far. They can be fun to culture on their own as a school project as well!
In the photo above, the yellow is the digestive tract. The black is a forming egg. The second photo is the top view. The antennae they use to swim with can be seen.
Tips 1 to 3:
1. For a steady supply, always have at least two cultures going, each placed in a different location. That way, if one culture crashes, you can rely on the other until the crashed one is back up and running.
2. Once you have an established culture, collect the tiny black triangular eggs that float on the surface before they sink. Dry them and save them in a container at room temperature. When immersed in water, they should hatch within 2 weeks.
3. You don't need many live daphnia or eggs to start a new culture. At 10-22C (50-75F), the culture can grow quickly if daphnia have constant access to an appropriate amount of food.
Setting up a New Culture
Larger Containers Are Better
Like with fish, larger-sized containers do better since the water parameters will change more slowly. The great thing is that all you need are plastic tubs. No need for glass aquariums. I have four containers going at any one time as I like a steady supply. In the winter, a 5 gallon one is outside on the grass, a 7 gallon, and two one gallon ones are in the garage. The 7 gallon is on the floor to take advantage of the cement floor's temperature moderating effects and the smaller two are on a shelf to take advantage of warmer air. In the winter, I have another 10 gal one against the house in the shade. Right now (early Nov.) the outside one is decreasing in population. No eggs are being produced as the cooler temperature has slowed the growth and there are few adults.
Used Aged Water
If you have water from an existing aquarium, use the water changes to fill the daphnia container. You can also squeeze out the filter floss from a mature hang on back or canister filter as food for them (just be sure there are no predatory cyclops or hydra in the tank it comes from as they will eat the daphnia). You can use rainwater. If you are starting with new tap water, let it sit for a month or so to start the aging process and for algae to start growing. Use a chemical to remove chloramines. I would rather start with a small amount of aquarium water and gradually add more as you do water changes that fill up a container right from the start. That way you add water volume as the culture grows.
Tip 4:
If filling from a garden hose, let the hose run for awhile to make sure no toxins from the hose are introduced to the water. Hoses heated in the sun release chemicals into the water and can kill the daphnia.
No Fancy Equipment is Needed
The daphnia tank does not need to have a bubbler or heater unless they are in warm temperatures above 22C (75F) or below 5C (40F). Use a bare tube (not an air stone- the tiny bubbles get caught in the carapace and cause them to float.) Toss in some duckweed, water lettuce or aquatic moss if you have it. This provides some shade and also a place for infusoria to live.
The photo above is a 4L glass jar seen from the side. The brown dots are daphnia. You can see the black eggs forming in some of them.
Feeding the Daphnia
As mentioned before, the amount of food is important when raising daphnia. Ideally, they need steady access to fine food particles and infusoria. Many people get frustrated trying to grow "green water" which is diatom algae that grows so thick the water turns a bright green color. This is not necessary. You can feed them the particles from an old filter or daphnia food.
A good recipe for food is equal parts of spirulina powder, wheat flour, rice flower, garbanzo bean flour, and tapioca flours. These flours are very fine particles and can be eaten the the daphnia. I also feed quick rise instant yeast activated yeast to vary the diet. Soak the yeast for about 5 minutes before feeding to start it's growth.
The key to feeding is to make sure there is enough food to feed the number of daphnia without it spoiling. Lots of food grows them fast, too much food kills them. Too little food starves them.
I feed them twice a day, just like my other fish. How much depends on how many daphnia are in the container. For the 7 gal culture, I use a 1/8 tsp measuring spoon and start by filling it with 1/4 of the spoon. Add more as the daphnia population grows.
Tip:
If you treat your cultures similar to your fish, feeding and checking them twice a day, doing water changes every other week or so, and carefully selecting tank mates, you can keep an eye on the population and overall health of the water.
Water Quality
It's pretty amazing for critters who thrive in temporary seasonal (ephemeral or vernal) ponds and literally puddles how sensitive they can be to water quality in a container.
Stirring the water can help to get the food particles in the water column for the daphnia to eat before adding more if you mis-calculate. If you notice a build up of stuff on the sides or bottom of the container over time, or a thick scum on the surface that may be an indication of poor water quality. Or the debris in long piles might mean you have blood midges!
If you notice there is a thick scum on the water surface, use a folded paper towel to pull the scum off. That usually means it is past time to change off some of the water. In nature, puddles are filled up with rain which dilutes the pollution and causes the scum (which is usually bacteria growth from organic material, pollens and microscopic dust) to drain off.
I check the water level weekly and top the container up in the summer when warmer water evaporates and also to replace the water I remove when collecting to feed.
Temperature can be a factor in causing daphnia to die off. Too high or too low or rapid daily temperature swings can do it too. If you locate your cultures where the temperature is relatively stable or change slowly over time, you will have more success. Temperatures over 22C (75F) can quickly kill your daphnia.
Culture Mates
Many people add a few ram's horn or bladder snails to the culture as the clean up crew. I feel this helps reduce the amount of extra food in case you miscalculate. The snail poop becomes food for infusoria. Daphnia also do well in blackworm cultures too.
In the spring to summer, uncovered containers will attract mosquitoes who lay their eggs in tiny black rafts on the surface. They look like tiny pieces of charcoal. If you are diligent to check their stage of growth, you can use them as free food for your fish. If you let them progress too far, they will add to the mosquito population. Covering the bin with a clear cover will prevent them and predators like dragonflies from laying eggs.
You may also notice small red wiggly insect larvae that make tiny houses of debris on the walls and bottom of the bin. Once they grow larger, they are easier to see and wiggle up to the surface to get air, then drift downwards. These are the much sought after "bloodworms". They start as jelly egg masses attached on the edge of the container or to floating plants. The adults are insects called "midges" looking much like mosquitoes but they do not bite. The babies are not worms at all, but insect larvae! Use a hand lens or microscope to see their tiny head and 6 front feet and two tiny false legs on the back end.
Avoid Introducing Predators
If you add water or plants from an wild source like a pond without observing it for a week or so for small critters, you risk adding the eggs or larvae of daphnia predators. These include: predatory copepods, hydra, ghost midges, some types of caddisfly larvae, damselfly larvae, dragonfly larvae and others. All of these can make great fish food, depending on the size of fish you are feeding.
Harvesting Daphnia
Once the population starts to build, you can remove small amounts of daphnia using a turkey baster from the dollar store or running a fine net through the container and putting them into water. Once established, I tend to feed my fish every other day. This allows the daphnia time to grow and reproduce. This keeps the daphnia from overpopulating and crashing.
Remember to turn off any external filter you have while feeding your fish or the daphnia will be sucked up. If you feed at the other end of the tank, and your filtration system is not very strong, you might might be able to get away with leaving it on. Sponge filters can usually be left running unless you have a very strong flow. Test a few first to find out.
My Observations on Daphnia Life Cycle
I am not convinced that our local temperate daphnia (west coast of BC, Canada) follow the same life pattern that the commercial daphnia from tropical environments. Tropical daphnia tend to hatch from eggs (ephippium which can overwinter and dry out contain many eggs) as females and the females reproduce themselves by having live babies (called parthenogenesis). Only when water quality declines are males born to the females. Those then mate with the females who then produce eggs. The adults die. The eggs first float to the surface, then sink to the bottom of the tank. They survive the drying out of the pond or puddle in the egg form and when the rains fill the ponds, the eggs hatch as tiny female daphnia.
So far, in my observations, the temperate eggs hatch as both male and female and the females do not produce live young either in our tanks or in the ponds and puddles they live in. They live and grow until adult size and then produce the eggs that float, then sink. We can have different-aged daphnia but that is likely because the eggs do not hatch all at the same time. By adding a few more eggs, we get different-ages of daphnia. Once the culture is producing well, it maintains a variety of sizes and ages of daphnia and eggs hatch into tiny daphnia. I suspect there are both male and female daphnia in all seasons for the eggs to be present. The males would look like immature females (like smaller adult females without a brood pouch). Can you find any photos or diagrams of male daphnia?
Update: I have started small cultures with just one adult daphnia. Each one did produce live babies, not eggs and the population grew from those. It is worth taking the time to experiment and find your own answers to questions like these!
Need a starter culture? Check out our live daphnia for sale for local pick up and our daphnia egg packs that we can mail within Canada.
