FILTRATION-RATES OF DAPHNIA-CUCULLATA ON ALCALIGENES-EUTROPHUS JMP134ESTIMATED BY A FLUORESCENT-ANTIBODY METHOD

The fluorescent antibody (FA) technique was employed to estimate the f iltration rates of Daphnia cucullata on the Alcaligenes eutrophus JMP1 34 strain introduced into lake water. We investigated the effect of an imal density and food concentration on the filtration rates in 0.2-mum filtered and autoclaved lake water. The individual filtration rates w ere 0.08-1.12 ml animal-1 h-1. Filtration rates decreased with increas ing grazer density and with increasing food concentrations. The grazin g impact on indigenous and introduced bacteria was compared in experim ents with 2-mum filtered lake water. Filtration rates of D. cucullata on A. eutrophus were greater than on indigenous bacteria. These differ ences were explained by size-selective grazing, implying that this mec hanism is important in the elimination of introduced bacteria from lak e water when the introduced bacteria are in the larger size-range of t he indigeneuos bacterial flora.