Making your own fish food can feel extremely rewarding, especially when you see how much your fish enjoy the treats you’ve provided. There are recipes all over the internet for creating different types of food for your fish, even age-specific food like foods appropriate for growing fry and foods that are best for grown fish. What many people may not realize, though, is that when it comes to treating your fish, you don’t have to actually make anything. Some foods make themselves, with a little support on your end. This is where daphnia come into the picture. Keep reading for more information on daphnia and how to culture them at home.
What are Daphnia?
Daphnia, sometimes also called water fleas, are tiny crustaceans that you have potentially seen in your tank before. They can get into your tank with new fish, plants, or invertebrates, and they are harmless to your tank’s inhabitants. Many fish, like goldfish, loaches, and cichlids, and amphibians, like salamanders, frogs, and tadpoles, all think daphnia are a delicacy and will happily gobble them up.
Image Credit: Ian Alexander, Wikimedia Commons
Daphnia are hardy crustaceans that can reproduce both sexually and asexually, so whether you have one or many, they’re able to reproduce in the right conditions. They are egg layers, and their eggs can withstand very harsh tank conditions, ensuring the survival of the next generation. Like shrimp, these crustaceans molt their hard exoskeletons as they grow. Each time females molt, they usually lay a clutch of eggs. Daphnia molt approximately every 8 days, so they can reproduce exponentially very rapidly.
They are very small but visible to the naked eye. They reach up to 3 mm in length when fully grown, but it isn’t uncommon for them to stay smaller than that. They are cute in their own unique way and watching their unusual swimming patterns can be a lot of fun.
These creatures are filter feeders, meaning they pull small debris and organisms from the water itself to eat. They are at an extremely low risk of “taking over” your tank or outcompeting anyone in the tank for food, especially if there are predators present in the tank that will eat them.
Image Credit: Rosser1954, Wikimedia Commons
How to Culture Daphnia
Get a Tank: In order to maintain a daphnia population, it’s best to have them in a separate tank from the predators they’re intended to feed. They can share a tank with dwarf shrimp and snails, though. In fact, this is encouraged. Daphnia tend to feed from the upper levels of the water, so having tankmates that will help keep things clean down below will help maintain the tank. It’s best to keep daphnia in a tank that’s at least 5 gallons. They don’t need a lot of depth, but they do require a large water surface area, so long tanks are recommended.
Set up the Tank: In nature, daphnia live in streams and creeks, so gently moving water will keep them happiest. Some people have success culturing daphnia in stagnating tanks, but this will lead to more upkeep for you, the potential for stinky aquarium smells, and potentially lower daphnia population density. An air stone, bubble line, or sponge filter is recommended for daphnia tanks to aerate the water and help with movement. Floating plants are a great addition to daphnia tanks since they like to spend time near the upper portions of the water level.
Treat the Water: Daphnia are extremely sensitive to chlorine. Any water you add to your daphnia tank should be treated before you add it to the tank. Like many invertebrates, daphnia are also sensitive to copper, so avoid using the hot water tap to fill your tank since this can lead to heavy metal leaching from the water pipes and avoid any copper-containing medications or fertilizers.
Get Your Starter: Daphnia starters can be purchased from multiple outlets online. You may even luck into a daphnia culture starter in your LFS. If you have a tank that has daphnia in it already, you could catch them and transfer them to a culture-specific tank and allow them to reproduce there. It’s not advisable to attempt to catch daphnia in the wild, even if you’re certain of the identification, since you also risk catching other crustaceans, invertebrates, and even parasites.
Feed Your Daphnia: Feeding your daphnia is extremely easy. There are a couple of ways you can feed them. Allowing algae growth in their tank can help maintain natural food stores. Some people allow the water in their daphnia tank to turn green with algae blooms before adding the daphnia. You can allow the water to green with the daphnia in the tank, but they are efficient eaters and cleaners and will likely not allow it to get very green. The best way to ensure your daphnia are eating enough is by adding yeast to the tank. Active dry yeast should be added to a little water to activate the yeast before being added to the tank. Daphnia can also be fed spirulina algae in wafer, powder, or flake form.
Harvest the Daphnia: Once your culture is established with a breeding population, you’re ready to start harvesting daphnia. You can easily harvest them with a fine mesh fish net swept through the upper levels of the tank a couple of times.
Image Credit: Nina Schlotz, Wikimedia Commons
Things to Avoid
Putting the tank outdoors: Some people prefer to keep their daphnia tank outdoors, and there isn’t necessarily anything wrong with doing it that way. However, outdoor tanks allow for the potential introduction of mosquito larvae, dragonfly larvae, and other parasites and dangerous creatures. You also have far less control over the temperature of outdoor tanks, making it harder to ensure survival and reproduction of your daphnia.
Not harvesting: Like any other animal, if daphnia overproduce, you’ll end up with a population crash. This is caused by limited access to food, overcrowding, increased waste production, and lower dissolved oxygen in the water. Even if you aren’t currently feeding your daphnia to anything, it’s a good idea to harvest them from time to time anyway to prevent problems with your population.
Too hot or too cold: Daphnia prefer to be kept in slightly cooler temperatures, usually around 64-72˚F, give or take. If they are kept too hot or too cold, they will stop reproducing. In extreme temperatures, you may even have a die off of your adult and juvenile population, leaving you with unhatched eggs as your only hope of the culture continuing. If you live in an area where your temperature stays stable most of the year, you may consider keeping your daphnia tank in a garage or similar structure. These tend to stay cooler than the outdoors, are more protected than the outdoors, and are less likely to experience rapid temperature changes than the outdoors.
Stagnant water: As previously mentioned, some people feel their daphnia do best with stagnant water. However, stagnant water can lead to issues with smells and is a harsh environment that is unlikely to support life for extended periods of time. Allowing your daphnia culture to live in stagnant water may lead to a population crash.
Culturing your own daphnia tank can be a fun project that allows you to treat your aquatic friends. Once the tank is set up and running, there is little maintenance you will need to do since the daphnia will work hard to keep the water clean. If you decided to culture daphnia, be ready to cull the population from time to time, whether that involves throwing some of them out, giving them away, or selling them. These fascinating, tiny creatures can be enjoyable to watch all on their own due to their feeding antics and rapid growth and changes.
Oliver (Ollie) Jones — A zoologist and freelance writer living in South Australia with his partner Alex, their dog Pepper, cat Steve, and 3 large aquariums full of fish and other aquatic creatures. Ollie, originally from the USA, holds his Master's Degree in wildlife biology and moved to Australia to pursue his career but has found a new love for marine life and writing about animals of all types. He hopes to share his aquatic knowledge and expertise with people so they can share in his passion.