FACTORS AFFECTING THE FOODS AND FEEDING PATTERNS OF LAKE-DWELLING RAINBOW-TROUT (SALMO-GAIRDNERII) IN THE NORTH ISLAND OF NEW-ZEALAND

Differences in feeding between age classes, males and females, and hatchery reared and wild rainbow trout (S. gairdneri) in Lake Rotoma are described. Analysis of results, in conjunction with other published data on trout foods and feeding, showed that there was a summer increase in epibenthic feeding which , in Lake Rotoma, was most apparent in the species of forage fish predated upon. When trout feeding on forage fish was examined in a variety of lakes, 2 trends emerged. In large, clear, oligotrophic lakes trout fed predominantly on smelt (Retropinna retropinna) which are shoaling, epipelagic fish. Trout in small turbid lakes fed mainly on the solitary, benthic bully (Gobiomorphus cotidianus). These differences in feeding on forage fish were associated with the effects of water temperature and turbidity on trout distribution and foraging behavior.