Аннотация:Behaviour and microhabitat selection by brown trout in two streams presenting severe winter conditions, were investigated in south-central Norway. Fish were studied by direct underwater observation in different habitat types, during day and night, and with simultaneous sampling for dietary analysis and invertebrate drift. During the day in winter, brown trout exhibited two different behavioural strategies, depending on fish size. Smaller fish (<25 cm) sheltered passively in the substrate or in submerged vegetation, and were almost never active during daylight hours. This behaviour was consistent throughout the winter until water temperatures rose in spring. Larger trout (25-60 cm) were actively aggregating in deep-slow stream areas during the day. During the night the trout exhibited a third behavioural strategy. The trout were active throughout the night from dusk to dawn, and this behaviour was consistent throughout the winter
