Prey selection byGalaxias vulgarisin the Hawkins River, New Zealand

Abstract

Abstract To determine the extent of prey selection by the nocturnally active fish Galaxias vulgaris, samples of fish, drift, and benthos were collected over a 24‐h period in summer in a stream draining the foothills of the Southern Alps in New Zealand. Feeding started after sunset, peaked by midnight, and virtually ceased by midday. Both drifting and benthic foods were consumed, and timing of peak feeding was synchronous with the period of greatest abundance of aquatic drift. Larvae of Austrosimulium spp., Deleatidium spp., and Aoteapsyche colonica comprised the major proportion of the prey eaten. Prey selection was indicated by the over‐representation of Austrosimulium spp. and under‐representation of both the smaller size classes of Deleatidium spp. and other aquatic invertebrates in the diet of fish. With the exception of the coleopteran Costelytra zelandica, terrestrial organisms were not eaten by fish, but several aquatic taxa were. Foraging by Galaxias vulgaris on drift and benthos may provide fish with greater prey options for feeding efficiently throughout the night.