Experimental Observations on the Effects of Predation by Goldfish (Carassius auratus) on the Zooplankton of a Small Saline Lake

Abstract

The short-term effects of various intensities offish predation on zooplankton communities were examined. Field studies indicated that fish predation was, as expected, size-selective: in the presence of fish, size distributions of the principal prey, Daphnia pulex, were skewed toward the smaller size-classes and the minimum size of egg-bearing D. pulex was also smaller. Fecundity of Diaptomus ashlandi, and probably also of Daphnia pulex, was greater with fish present. This caused the abundance of these two dominant species to increase initially with increasing predation. Subsequently, the species declined at higher predation levels in order of their interest to fish, with large D. pulex[Formula: see text] declining before small D. pulex (< 1.35 mm) and both groups doing so at lower predation levels than Diaptomus ashlandi.