Daily Feeding Periodicities, Food Uptake Rates, and .Dietary Changes with flour of Day in Sorne Lake Fishes'

The feeding periodicities of five common cohabiting fish species in Lake Opinicon, Ontario, were defined for the early summer period of accelerated feeding by determining the mean weights of stomach contents per gram of body weight at intervals of 2–3 hr throughout the 24-hr cycle. Two, and in sunfish three, feeding peaks per 24-hr period were indicated. Perca flavescens was diurnal; Lepomis macrochirus, L. gibbosus, and Fundulus diaphanus were largely diurnal (with a nocturnal component); and Ambloplites rupestris was equally nocturnal and diurnal. In the two sunfish there were clearcut differences in the organisms eaten by day and night. The technique developed here is a useful method for determining the mean minimum daily ration for a population of fish in the field. The results are comparable with those obtained by other workers in aquarium feeding experiments.