Continuous Culture of Daphnia Magna

What is Daphnia Magna?


Daphnia Magna lives in freshwater. They are cladoceran crustaceans and their common name is “water fleas.” They are tiny and hop in the water while they move. Thus, they get the name water flea. Daphnias are available almost all over the world and are famous for their two types Magna and Moina. The body of Daphnia Magna comprises a head and a chest. They have two antennae which they use for locomotion. The eyes, located on both sides of the head and are covered with thin skin. Their chest is enclosed with an external skeleton that sheds periodically. The females have a brood pouch in the belly.

It is brought up as live food for pet fish. These keep the fish in excellent health and ideal size. Fish, especially cyprinids get the essential nutrients from daphnia for spawning.

How to Culture Daphnia

Daphnia Magna culture is easily possible in any non-toxic water-filled container at home. Use dechlorinated water or let the tap-water age before you use it for the culture. An aquarium is more suitable for beginners to track the progress of the culture. Keeping the water at up to 20° Celsius temperature is ideal. Temperature above this level can obstacle reproduction. Culture can be more successful in warmer days of summer but not much yield is expected.

a. Feeding the Daphnia Culture

• Spirulina algae
• Chlorella algae
Green water rich with Scenedesmus or Ankistrodesmus algae
• Baker’s Yeast
• Microfeast
• Split pea soup mix in powdered form
• Artificial Plankton, Rotifer
• Whole-wheat flour

Practically, the active baker’s yeast and chlorella algae are the most effective and easy foods for the culture. To improve the colors of pet fish, add powder form of paprika to flour or soup mix. The ratio is paprika is 1:10 flour or soup mix. Daphnias that consumed paprika will provide fish the necessary nutrients to improve coloration.

The method of feeding the culture is as follows:

Monitor the population of daphnia in the tank. A cuvette with a wooden rod or a test tube can be useful to count the daphnia. Knowing the number of daphnia per millimeter will help to determine the amount of food. For 0 to 1 daphnia per millimeter in 80 liters of a water tank, add 1/8th teaspoon of powdered food, 1 to 4 daphnia ¼th teaspoon per day and so on. Do not overfeed because leftover food can root and encourage the growth of bacteria which can eventually lead to the death of many daphnias.

Amount of the food can be also determined by experience in the home culture of daphnia. The hint is not to overfeed the culture. Feeding less will always be better than overfeeding. So, the amount can be considered by the trial and fail method starting with a small amount of food.

To feed the culture, add the powdered food directly to the water container until it becomes cloudy. The next day it should be crystal clear again if the food amount is at the proper level. If the water is still opaque after one day, this is a sign that the culture fed too much. In case, the water is cleared in lesser than one day then this means the food amount is insufficient to the culture.

b. Changing the Water

Changing water at harvesting time is the ideal way to make water changes and refreshing the environment. For changing water use a fine screener able to harvest all the daphnia, including babies. Drain the water from the culture tank over the screener until the tank becomes empty. Try also not to drain the debris at the bottom. Feed some part of the daphnia to the fish or deep freeze to feed later. Drain the bottom level into a separate bucket or container. Add some fresh, chlorine-free water to this container to make siphoning the left daphnia easier. Wait for the debris to settle and siphon the remaining daphnia and screen them. Combine them with the previously harvested.

Clean the culture tank and fill fresh water. Make sure that the new water is chlorine-free or it will be lethal for the daphnia. Release the remaining water fleas after feeding in the refreshed and cleaned culture tank. Keep feeding them as per your usual routine.

c. Health and Care of the Culture

Daphnia tank must stay clean from any infestation for healthy growth. If daphnia count is not reaching 10+ per 20 ml after several weeks of starting the culture, there is possibly a bacterial growth in the tank exists. Hydra, flatworms, and other tiny insects can be also lethal for daphnia. If anytime these appear in the tank, discard the culture; clean and disinfect the tank for making a new culture and selectively collect the healthy daphnia.

The number of daphnia per 20 ml must be above 10. When they reach a higher density, the culture is ready for harvesting, but 10+ per 20 ml should remain in the culture. Since in the home cultures, it is not possible to count daphnia, it requires to have the practice to determine the correct density of daphnia. You can visually try to observe the amount in the culture when it tops.  Then, try to not exceed this amount after each harvest and culturing period. The best method for the starters is to harvest the culture after one week but no more than half of the daphnia.

Culture tank needs a thorough cleaning if the culture has become quite old. The debris collected on the walls and bottom of the tank is a sign of alarm for a possible collapse. Scrap the bottom of the tank and empty it in another container. The debris will settle and daphnia will be hopping in the water. Pour them into the newly changed water and throw away the debris. Excessive dirt in the tank does not let the culture grow properly.

Introduce some snails or any type of oligochaete worms in the culture tank. They keep the tank clean and eat left-over food. Overabundant snails or worms need to be removed. They can be also another source of food for some aquarium fish. Some kinds of worms that stay at the bottom of the tank can be cultured together with daphnia. For instance, these can be such as tubifex and California blackworms. In this case, slightly more food will be necessary, so that worms can also get feed on what settles in the bottom.

Strong aeration of the tank is essential as it keeps the feed suspended in the water where daphnia can easily feed on it. If it settles down in the bottom, only the snails and the worms can consume it.

All the above care tips help the culture growing fast. 110 to 140 grams yield of Daphnia can be obtained every week from a culture tank of 150 liters.

Important Notes


• Baker’s dry yeast keeps the culture reproducing more rapidly while the soup-mix gives the daphnia health and strength.

• Many other unconventional types of food like alfa alfa meal, powdered trout chow, live phytoplankton, yeast, soy flour or apple-snail manure are a good feed for daphnia culture. Often the microorganism that grows on decomposing of these foods serves the purpose of being a suitable feed for the culture.

• The quantity of the decomposing food must not grow large otherwise it will bring the water quality down. Oxygen may deplete; nitrates, phosphates, ammonia, and nitrites will increase and daphnia will die.

• Overgrowing phytoplankton in the water consumes the phosphorus in the water. They eat phytoplankton and the low levels of phosphorus indicate daphnia abundance of food and hence they reproduce more. That is why, change the water, keep it clean and low in phosphorus level to encourage culture growth.

• It is strongly recommended to keep snails or oligochaete worms in the culture tank to consume uneaten food, not leave it to rot and create harmful bacteria. Also, the shells of the snails do the work of bio-media to host nitrify bacteria.

• To succeed stick to this schedule strictly: feed > water change > harvest. Forgetting any of these steps on time can reduce the yield and make your efforts not worth it.

• When daphnia is going to be collected from outdoor water sources, pick only a few of them and make sure you do not pick any planaria or hydra with them. These organisms are the enemy of daphnia and can kill your entire culture in a short time. Contaminated water can also contain flatworms, hydra or the eggs of these. So, pick daphnia enough only for a new culture setup.

• Micro-sporidean is a type of parasite. If the daphnia gets this, it becomes opaque or white. In this case, discard your entire culture, clean the tank and equipment, then set a new culture.

• A colony of daphnia comprises of young, adults and grown-ups. No age level should overgrow the other levels. If you have more grown-ups, harvest them and feed them to the fish. They eventually die after 21 to 28 days of their birth. And the population of too many adults may be a sign of possible collusion of the culture. So, harvesting, water change and feeding at that time will be a good practice.

• In suitable conditions, daphnia reproduces by parthenogenesis. This way the females need no male and from their eggs, all-female colonies develop. If the conditions are bad like lack of food, unclean water, unsuitable temperature, etc. the female daphnia gives birth to a few males also. These males mate with the female and after this mating female lays eggs that are extremely tolerant of hard conditions. The name of this king of eggs is ephippium. They rest on the back of the female and can easily be seen from close observation. That kind of development in culture is a clear and serious indication that the tank needs a proper schedule of feed –> water change –> harvest. Otherwise, the culture will collapse and all the females will die after developing resting eggs.

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