Diel foraging and shelter use of large juvenile brown trout (Salmo trutta) under food satiation

The natural partitioning of juvenile brown trout Salmo trutta foraging behavior is controlled by a number of factors including predation risk, competition, temperature and food availability. The present study uses PIT-tagging and visual observation to assess the use of shelter and foraging behavior of Danish wild juvenile brown trout (13.5–15.6 cm). The experiment was conducted in a fluvarium and the fish were fed to satiation. It was hypothesized that food satiation would promote nocturnal foraging and increase daytime shelter use. Our results showed a significant difference in shelter use between day and night with a significant increase in shelter use during daytime conditions. Visual observations showed a significant preference for nocturnal feeding. Together with the significantly reduced shelter use during the night, our results support the hypothesis that young stream living trout only feed during the day to the extent needed to sustain growth.