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 re lation to environmental variables and fish swimming activity, from aut umn to spring. There was marked seasonal variation in feeding behaviou r, indicating a reduction in appetite from autumn to winter and a rapi d increase in appetite from late winter onwards. Seasonal variation in behavioural indices of appetite was more closely related to day lengt h and change in day length, than to other environmental variables, inc luding water temperature. A feeding regime based on the assumption tha t water temperature is the most important environmental determinant of the appetite of salmon in sea cages could lead to food wastage in aut umn 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 differe nt 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, a nd pre-feeding swimming speed was not closely related to appetite.