Daphnia

Daphnia magna is a species of Daphnia (a cladoceran freshwater water flea) which is native to northern and western North America. It is also widely distributed in Eurasia and in some regions of Africa.

D. magna is specified to be used in the OECD Guidelines for the Testing of Chemicals, Tests No. 202 "Daphnia sp., Acute Immobilisation Test and Reproduction Test", and Test No. 211 "Daphnia magna Reproduction Test". Test No. 202 is a 48 hour acute toxicity study, where young Daphnia are exposed to varying concentrations of the substance under test and the EC₅₀ determined. Other Daphniaspecies than D. magna may occasionally be used, but labs mostly use D. magna as standard.