The dependence of the assimilation efficiency in Daphnia magna on the 14C-labeling period of the food alga Scenedesmus acutus

The efficiency of carbon assimilation in Daphnia magna was estimated as a function of the 14C-labeling time of the food alga Scenedesmus acutus. The assimilation efficiency of 14C was up to 24% higher at low labeling times (≤ 1.4 generations) (P < 0.05) than at high labeling times (≥ 4.2 generations). In uniformly labeled cells the assimilation efficiency in D. magna was 71 ± 2% SE. Variation in the assimilation efficiency with labeling time is associated with change in the relative distribution of 14C among the different cell compartments in the food alga. Uniform labeling of algae is achieved effectively via exponential growth over several generations in batch cultures from sparse inocula.