Culturing Daphnia (Water Fleas) as Live Food

How to culture Daphnia, a nutritious live food and natural roughage for juvenile and adult fish, covering container, feeding, aeration, harvesting and avoiding population crashes.

What Daphnia are

Daphnia, commonly called water fleas, are small planktonic crustaceans about 0.2 to 6.0 mm long. The two species most used in the hobby are Daphnia magna (larger) and Daphnia pulex (smaller). They are filter feeders that eat unicellular algae, bacteria, protists and fine organic detritus, and they reproduce rapidly, mainly by parthenogenesis, so populations can boom and then crash quickly.

Why feed Daphnia

Daphnia are a nutritious live food popular for juvenile and adult fish, and their chitinous shells act as roughage that can help fish digestion. Because cultured Daphnia are raised in a controlled container rather than collected from wild waters, they avoid the disease and parasite risks associated with wild-caught live foods such as tubifex.

Setting up a culture

Use a container with more surface area than depth, filled with aged, dechlorinated water, and keep it at a moderate temperature around 20 deg C (68 deg F). Daphnia are attracted to light, so a light kept on the culture helps. They are sensitive to water quality, so a partial water change (for example replacing about half) every few weeks helps keep the culture stable.

Feeding

Feed Daphnia on suspended foods such as active dry yeast, spirulina powder or green water (live algae). A useful rule is to feed only once the water has cleared, which shows the previous feeding has been consumed; overfeeding fouls the water and is a common cause of crashes.

Aeration and harvesting

Gentle aeration helps keep food suspended; a coarse air stone giving medium-sized bubbles is suitable, positioned so the Daphnia can move to a calmer area, whereas very fine bubbles can lodge under the carapace and harm them. Harvest by drawing a fine-mesh net through the dense population near the surface; a healthy culture tolerates frequent, heavy harvesting.