Mechanisms Regulating the Feeding Rate of Daphnia Magna Straus

Feeding regulation by the plank tonic crustacean Daphnii magna was studied in increasing concentrations of two foods: Chlorella vulgaris and Saccharomyces cerevisiae. Direct observation studies show that feeding rate is proportional to concentration of food only below a 'critical concentration'. Above this critical value further increase in concentration of food has little or no effect on feeding rate. Daphnia was shown to regulate collection and ingestion of food by decreasing pumping rate and rejecting excess food from the food groove. The amount of food present in the animals' gut prior to an experiment also affects feeding rate of Daphnia in food suspensions above the critical concentration. Results show that animals, prefed at a very low rate (1/10 maximum rate) do, for a short time, feed more rapidly than those prefed at the maximum rate. These results are considered in relation to those of Ryther and Rigler for free-swimming Daphnia magna.