DAILY FEEDING RHYTHMS IN ATLANTIC SALMON .1. FEEDING AND AGGRESSION IN PARR UNDER AMBIENT ENVIRONMENTAL-CONDITIONS

Daily feeding patterns of tank-reared Atlantic salmon Salmo salar parr under ambient conditions and their relationship with patterns of aggr ession were investigated during spring and autumn. A single, early aft ernoon feeding peak was observed during spring but no consistent patte rn emerged from the autumn trial (fish did tend to feed in synchrony, even though the population's feeding pattern varied between days). Agg ression was highest at first light during both spring and autumn, redu cing thereafter throughout the day. Feeding and aggression were out of phase during spring, with the level of feeding increasing as aggressi on decreased. It is suggested that the high levels of early morning ag gression are associated with re-establishment of the social order that breaks down after a period of darkness; in the spring this may have i nhibited feeding. (C) 1997 The Fisheries Society of the British Isles.