Food used for Ceriodaphnia dubia in culture and toxicity testing should be uniform, adequate, and easily prepared. Using as a control the current standard food, YCTF, the authors tested a variety of foods made with algal species singly and in combination, prepared with several methods of freezing and freeze-drying. The measure of food usefulness was a combination of survival and reproduction over a 7-day period. Foods based on single algal species were not as useful as those with a mix of species, and the easily used freeze-dried foods were better than the frozen preparations. Several commercial plankton foods, including yeast, algae, microcapsules and microparticulates, failed to support Ceriodaphnia adequately. In a separate series of experiments, the authors tried freeze-dried YCTF mixtures as a food. The preparation proved consistently capable of supporting good growth and reproduction of Ceriodaphnia.