Ammonia-nitrogen excretion in Daphnia pulex

Abstract

Ammonia-nitrogen excretion rates were measured in natural summer and cultured populations of Daphnia pulex from Silver Lake, Clay County, Minnesota, USA during 1973. The mean rate of ammonia-nitrogen excretion for the summer populations was 0.20 µg N animal−1 day−1 or 5.11 µg N mg−1 dry body weight day−1 (N = 80) measured at 15°, 20°, and 25°C. These rates appear to be temperature and weight dependent, but they are probably affected by factors other than temperature and dry body weight. Ammonia-nitrogen excretion rates of Daphnia pulex cultured on Chlamydomonas reinhardi yielded the following relationship with temperature: Log10E = (0.061) T 1.773, where E is µg N animal−1 day−1 and T is temperature °C. The ammonia-nitrogen excretion on a mg−1 dry body weight day−1 basis was related to temperature according to the following similar expression Log10E = (0.043) T + 0.153, where E is µg N mg−1 dry body weight day−1, and T is temperature °C. The length-weight relationship of Daphnia pulex for the summer populations (N = 1583) was log10W = (0.526) Log10L + 1.357, where W is weight in µg and L is length in mm.