DAILY FEEDING RHYTHMS IN ATLANTIC SALMON IN SEA CAGES

The swimming activity and feeding behaviour of 1-kg one-sea-winter Atlantic salmon were investigated in a production sea cage during June-July 1989. The fish were fed at feed manufacturers' recommended rates using automated feeders that dispensed food regularly throughout the daylight hours. The routine swimming speed of the fish and the number of fish that responded to a standardised food presentation were measured using an underwater video camera. Both appetite and swimming speed showed the same marked daily rhythm, being highest in early morning and evening, and lowest in early afternoon. The state of the tide had little effect on either variable. A combination of swimming speed, time of day and time of tide explained 59.3% of the variation in appetite. The results suggest that feeding efficiency could be improved markedly if feed delivery was tailored to daily rhythms in appetite.