Daphnia (water flea) (Daphnia magna) care guide

Group
Other invertebrates
Other names
Water flea, Giant daphnia, Daphnia
Family
Daphniidae
Origin
Widespread across the Northern Hemisphere, in lakes, ponds and rock pools; also brackish water
Water
freshwater
Maximum size
0.5 cm
Temperature
10–24°C
pH
7–8.5
Hardness
moderate to hard
Minimum tank
10 litres
Care level
beginner
Temperament
peaceful
Lifespan
Under 0.5 years

Care

Daphnia magna is a large water flea, a tiny crustacean of 1.5–5 mm in a see-through shell, with two branched antennae it uses to swim in jerks and one large eye. Females reach about 5 mm, males about 2 mm. It lives in still water across the Northern Hemisphere, from lakes and ponds to pools by the sea, and tolerates more salt than other Daphnia. It is the standard animal used in water-toxicity testing. Use: it is one of the best live foods for small and young fish, and it is sold as live cultures and frozen. A live culture keeps fish busy and helps clear green water. Culture: a container of 10 litres or more of dechlorinated, aged water, gentle or no aeration and light. Feed green water, a little dried spirulina or a pinch of active yeast every few days, just enough to keep the water slightly cloudy; overfeeding crashes cultures. Change some water weekly. Room temperature suits it; the figures here are general guidance. Wild collecting: Daphnia occur in British ponds, but collecting from the wild can bring in pests such as hydra, dragonfly larvae, leeches and fish diseases, and it is not allowed on many waters. Buy starter cultures instead. Copper: copper-based medicines and some plant fertilisers are toxic to shrimp, snails and most other invertebrates. Never treat a tank holding them with copper, check the label of any fertiliser or medicine, and keep nets and buckets used for copper-treated tanks separate. Daphnia are extremely sensitive to copper and other pollutants. Sources: Wikipedia (en.wikipedia.org/wiki/Daphniamagna). Checked October 2026.

Diet

A filter feeder on suspended algae, bacteria and detritus. It can also graze algae films and sediment. In culture feed green water, spirulina powder or a little yeast.

Breeding

Reproduces very quickly by cyclical parthenogenesis: in good conditions females produce clutches of up to 100 eggs every three to four days without males, and the young are female copies. When conditions worsen, males appear and females make resting eggs inside a tough case (ephippium), which survive drying and cold and hatch later into females.

Compatibility and tank mates

Harmless. Almost all fish eat it; add it to fish tanks as food. Keep cultures in a separate container.

Last updated 8 October 2026. Community-edited care guide on Aquatic-Auctions.

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