DAILY AND SEASONAL PATTERNS IN THE FEEDING-BEHAVIOR OF ATLANTIC SALMON (SALMO-SALAR L) IN A SEA CAGE

The diurnal and seasonal variation in behavioural indices of appetite in one-sea-winter Atlantic salmon in a sea cage was investigated in relation to environmental variables and fish swimming activity, from autumn to spring. There was marked seasonal variation in feeding behaviour, indicating a reduction in appetite from autumn to winter and a rapid increase in appetite from late winter onwards. Seasonal variation in behavioural indices of appetite was more closely related to day length and change in day length, than to other environmental variables, including water temperature. A feeding regime based on the assumption that water temperature is the most important environmental determinant of the appetite of salmon in sea cages could lead to food wastage in autumn and early winter and under-feeding in late winter and early spring. The responsiveness of salmon to food varied significantly throughout the day, but the diurnal pattern of appetite was different at different times of year. In contrast to a previous study at the same site in summer, there were not marked morning and evening peaks of appetite, and pre-feeding swimming speed was not closely related to appetite.