Size Selection of Daphnia pulicaria by Yellow Perch (Perca flavescens) Fry in West Blue Lake, Manitoba

Abstract

Prior to mid-July, Daphnia pulicaria in yellow perch (Perca flavescens) fry stomachs were smaller than those in plankton collections but after this date mean lengths of D. pulicaria in stomachs and collections were similar indicating an initial selection for small D. pulicaria by the fish. The relation between D. pulicaria body depth and perch mouth gape width indicated that perch fry less than 18 mm long, a length attained in mid-July, could not readily ingest D. pulicaria with body depths greater than 0.7 mm (1.3 mm long). The heterogenic relation between growth in mouth and body size enabled perch fry in West Blue Lake to quickly utilize, as an energy source, the abundant D. pulicaria population.