Toward a standard Daphnia juvenile production test

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Abstract
The Daphnia 21‐d juvenile production test was ring tested in 1985. The results showed maximum variability, that is, the effective concentration ranged from less than the lowest concentration to greater than the highest concentration. At a workshop on this subject in 1989 several contributory factors to this variability were identified. This paper describes two experiments designed to investigate these factors, specifically the species of algae supplied as food, the ration, the age of algal culture used to feed the daphnids, and the influence that daphnid medium renewal frequency had on fecundity. The results show that, at comparable feeding rates (as milligrams of carbon per liter of culture medium or milligrams C per daphnid), a diet of Selenastrum resulted in higher fecundity than one of Chlorella or Scenedesmus. However, the use of either species of algae at rations between 0.5 and 1.0 mg C per liter (equivalent to 0.1‐0.2 mg C per daphnid) would meet the revised Organization for Economic Cooperation and Development (OECD) test acceptability criterion for mean control fecundity of ≥60 juveniles. Furthermore, animals experiencing renewal of their medium three times each week produced significantly more juveniles than animals whose medium was renewed less often. The age of the algal culture used as food did not influence fecundity.