Filtering rates on [ 3 H]thymidine-labelled natural unattached bacteria and that on [ 14 C]bicarbonate-labelled natural plankton which pass through the 25 μm-mesh-size screen were measured for Daphnia longispina and Eodiaptomus japonicus in Lake Biwa. Errors associated with the radioisotope technique, i.e the loss of labels after feeding trials and the self-absorption of the beta emittance of 3 H, were checked and corrected for the calculation of the filtering rates. It was suggested that Daphnia collects bacteria efficiently, although the efficiency is somewhat variable depending on food particle composition (i.e. presence and absence of larger particles) and feeding condition (i.e. animal density and physical disturbance). By contrast, copepodites of Eodiaptomus were suggested to be less efficient bacteria feeders. Food resource exploitation strategies of these two co-existing zooplankters are discussed.
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Nagata et al. (1988) studied this question.