Recent studies have demonstrated that Daphnia, a cladoceran (anomopod) zooplankton species with a high phosphorus content, can become P limited when fed algae deficient in phosphorus. Bosmina is another common anomopod zooplankter, but its body has a lower percentage of P than does that of Daphnia, and Bosmina might therefore be less susceptible to P mineral limitation. To test for this hypothesized interspecific difference in nutrition, Bosmina and Daphnia were raised on two food types: P-deficient or P-sufficient Scenedesmus acutus in two concentrations (0.2 or 1.0 mg C L-1). As predicted by its lower P content, Bosmina growth and fecundity were not affected by the P content of algal food, even though P-deficient food caused significant declines in these life history parameters for Daphnia. Results suggest that Bosmina has a lower P requirement than does Daphnia and that Bosmina may process phosphorus more efficiently or be better able to survive losses in body P content. The outcome of competition between Bosmina and Daphnia therefore might shift in favor of low-P-content zooplankton such as Bosmina under conditions of seston P mineral limitation.