Diel patterns of feeding and prey selection in giant kokopu (Galaxias argenteus)

We examined diel variation in prey selection by giant kokopu, Galaxias argenteus, in relation to diel variation in the abundance of drifting invertebrates in a second order stream in Otago, New Zealand in summer. Clear differences in both the quantity and composition of prey consumed was evident. Greater numbers of aquatic insects were consumed at night relative to the day, whereas more terrestrial insects were consumed by day relative to the night. Giant kokopu were selective in the prey consumed. Trichoptera dominated giant kokopu diet at night even though drift samples collected at night were dominated by Deleatidium mayflies. Results suggest that giant kokopu feed actively during night and day in summer, and that prey selection is influenced by interactions between factors including prey availability, prey characteristics and light.