Despite the widespread use of Daphnia magna as a test organism in bioassay studies, little attention has been devoted to conditions necessary for culturing healthy animals in the laboratory or to the quality and quantity of foods required during chronic life-cycle bioassays. Growth, reproduction, and survival in daphnids are very dependent upon the quality and quantity of their food. Different algal species and artificial diets have been recommended as foods for Daphnia but the impact of these foods on the health and reproduction of test organisms has not been carefully analyzed. We used the appearance of individuals (including the presence of lipid reserves), growth, reproduction, and mortality as criteria for evaluating the suitability of three different food types and food concentrations for chronic life-cycle tests and for determining the maximal duration for chronic life-cycle tests that will consistently yield reliable results. The three foods used were (a) a 1:1 mixture of two algal species, Ankistrodesmus falcatus and Chlamydomonas reinhardtii; (b) Selenastrum capricornutum, a green alga often used in bioassay tests; and (c) trout chow (PR-11) and baker's yeast, an artificial food diet.

We recommend that a diet of green algae be used in the culture and feeding of animals in life-cycle tests and that a food concentration of 1.25 mg dry weight of algae per litre of test water be provided for individual cultures daily. If the animals are fed three times a week, then 2.5 mg of algae should be used. We further recommend that lifecycle tests be run for 21 rather than 28 days to minimize the chance of low survival rates in control vessels. Methods are also described for culturing both D. magna and its food for use in life-cycle tests.