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 photoperiod) affect rates of food intake in fish. In species with variable life-history patterns, individual appetite might vary with the developmental strategy adopted in response to differing nutritional requirements. There may also have been selection for appetite to vary with the anticipated natural availability of food. 2. This study examines how appetite 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 marked peak in food intake in May of their second summer followed by a sudden loss of appetite (measured both as appetitive behaviour and as actual food intake); this anorexia was unrelated to temperature and may be an adaptation to anticipated seasonal variation in natural food availability. 4. Fish compensated for a reduction in the fat content of the diet by increasing their intake rate (after a period of reduced appetite). Early in the winter, fish with a low lipid content had an enhanced appetite, but this response disappeared as the winter progressed, probably because the need to maintain energy reserves diminishes as the winter progresses. 5. Sexual maturation in males had no consistent effect on appetite, although there was some evidence for a reduced intake a few months prior to spawning.