Nocturnally constrained foraging of a lotic minnow (Rhinichthys cataractae)

Abstract

Diel periodicity in foraging activity of the longnose dace (Rhinichthys cataractae) was determined by measuring dace activity over the stream bed, gut fullness, and the digestive state of prey items. Although most species of minnows are either diurnally or crepuscularly active, dace began foraging within 1 h after sunset with light levels near 10 lx and ceased before sunrise throughout the ice-free period. During the day few prey were taken as the dace remained under the shelter of stones. This nocturnal foraging pattern did not appear to be affected by spawning or seasonal changes in prey composition. Nocturnal foraging in dace is not likely a response to prey availability, but may be a response to avoid diel periods when salmonid competitors or visual predators are active.