There are probably as many methods for culturing daphnia as there are people making the attempt. But what most agree on without question is that daphnia makes an excellent (although not exclusive) food for tropical fish, including killifish.
There are two species of these small free-swimming shelled crustaceans, Daphia pulex (fairly small and dark colored), and D. magna (larger and pale colored). Daphnia can be collected from the wild or they can be cultured, although cultures do tend to experience normal “bloom and bust” cycles. This problem can best be dealt with by having several cultures active at any one time, so when one fails another is still producing.
Daphnia have long been a staple of the aquarium hobby, and have been successfully cultured in a variety of containers, from small buckets and indoor aquaria to outdoor stock tanks, ponds, and children’s wading pools.
Proper water for daphnia culture is not a major concern; they have been raised in hard well water and in soft rainwater.
“I keep my daphnia in a 300 gallon stock tank,” says Barry Cooper. “I [first] filled it with tap water (well water, 180 ppm, pH 7.5), added some soluble fertilizer, and watched it go green. Then I added a culture of mixed Daphnia species.” The next year it filled with rainwater and had lots of dead leaves, mostly ash and maple, fairly clear, reddish brown water, and it teemed with daphnia. Resting eggs had survived over the winter and hatched when the tank filled in the spring.
Gary Sutcliff uses small plastic wading pools kept outside. He feeds the daphnia in the spring with yeast and pea flour, which gets them off to a good start. “It’s important to harvest heavily when they bloom,” he says. “In any culture you want the population to be on the growing part of the curve.” His daphnia occasionally disappear for about a month, but then came back.
Robert Nahn uses a slightly different setup. “I have three big 32 gallon plastic containers, one with green water and about 10 comets [goldfish].” The other two containers are for daphnia culture. Every few days, he collects daphnia from the culture tanks, feeds the daphnia cultures with green water fom the comet tank, and then feeds the comets with flake food. The cycle works.
Opportunistic filter feeders, daphnia have been successfully raised on green water, yeast, powdered pea soup mix, alfalfa meal, skim milk, and a variety of other foods, commercial and homemade, as well.
Charley Grimes, writing in Aquarium Fish Magazine (“Feeding Live Foods”), found that his best results with daphnia occurred when he fed mashed sweet potato baby food mixed with water, up to twice a day. “I prefer the baby sweet potatoes [because] they make the daphnia a reddish color that I like.” Neither the daphnia nor the fish they’re fed to seem to have a particular color preference. Charley’s daphnia culture tanks have an airstone for water movement and receive 50% water changes weeky. When doing water changes, use a strainer, a piece of old tee-shirt, or a fine mesh net to recover any daphnia, then return them to the tank. Eventually, you’ll have to remove the mulm buildup. Siphon it into a bucket, let it settle , then recover any daphnia you’ve missed.
Many feel that greenwater is the best food for daphnia cultures. It can be produced by keeping the containers in sunlight and feeding them with well composted cow or horse manure or fertilizer. Other foods that will help keep a daphnia culture producing include:
Powdered milk (produces a 5-15 day daphnia population curve).
Soy flour recipe. Blend together 2 tsp. soy flour, 1 multivitamin tablet, 1 spirulina vitamin tablet (from a health food store) and 6 oz. water. In a separate container put 8 oz. tank water and a pinch of yeast; allow to sit for 20 minutes. Add two teaspoons of the soy flour mix to the tank water, then feed some of this mixture to the daphnia. The rest can be stored in the refrigerator.
Vegetable juice mix. Juice together some spinach, a carrot, and a beet (optional). Feed about 1 teaspoon of the mixture at a time. Store the balance in the refrigerator, or freeze in ice cube trays; feed a cube as required.
One critical thing that daphnia need, besides a steady food source, is plenty of light. Recommendations vary, but lighting may reach 24 hours per day without harm, as long as the water temperature remains below the mid-70s (F). At higher temperatures the daphnia may go dormant. With cooler temperatures, the daphnia usually will resume active growth and reproduction.
— G.C.K.A. Newsletter, January 1998