PRONOUNCED SEASONAL DIFFERENCES IN APPETITE OF ATLANTIC SALMON PARR, SALMO-SALAR - EFFECTS OF NUTRITIONAL STATE AND LIFE-HISTORY STRATEGY

1. External environmental influences (such as temperature and photoper iod) affect rates of food intake in fish. In species with variable lif e-history patterns, individual appetite might vary with the developmen tal strategy adopted in response to differing nutritional requirements . There may also have been selection for appetite to vary with the ant icipated natural availability of food. 2. This study examines how appe tite in Atlantic salmon parr varies seasonally, and how this seasonal variation is influenced by (a) diet quality, (b) nutritional status of fish and (c) sexual maturation in male pan: 3. All fish showed a mark ed peak in food intake in May of their second summer followed by a sud den loss of appetite (measured both as appetitive behaviour and as act ual food intake); this anorexia was unrelated to temperature and may b e an adaptation to anticipated seasonal variation in natural food avai lability. 4. Fish compensated for a reduction in the fat content of th e diet by increasing their intake rate (after a period of reduced appe tite). Early in the winter, fish with a low lipid content had an enhan ced appetite, but this response disappeared as the winter progressed, probably because the need to maintain energy reserves diminishes as th e winter progresses. 5. Sexual maturation in males had no consistent e ffect on appetite, although there was some evidence for a reduced inta ke a few months prior to spawning.