Seasonal Energy Budget of Brook Trout in Streams: Implications of a Possible Deficit in Early Winter

Abstract

The seasonal diet and energy budget of brook trout Salvelinus fontinalis were investigated in three southern Ontario streams in 1983–1984. Stomach analyses were performed and the calculated energy value of prey items was compared with the calculated energy required for maintenance metabolism (both sets of calculations were based on literature values). Brook trout continued to feed throughout the winter, consuming a variety of prey species, especially insect larvae. Condition (weight˙length−3) declined markedly from late summer (August) to early winter (November-December) and remained low until spring (May), indicating a depletion of reserves despite the continued feeding. It appeared that low winter temperatures restricted the rate of food consumption (due perhaps to a direct effect on gastric evacuation rates) which thereby limited energy intake. This restriction is believed to be responsible for the metabolic deficit condition when minimal costs of maintenance metabolism could not be offset by energy intake. In November and December, this deficit occurred in two of six instances for immature brook trout and in four of six instances for mature brook trout. In the stream, where groundwater minimized temperature fluctuation, winter deficits only occurred in reproductively spent brook trout. Acclimatization to rapidly declining temperatures in early winter, coupled with reproductive costs for mature fish and an insufficient energy intake, resulted in the depletion of energy stores. In November-December, such a condition may limit the extent to which fish can survive unusually long winters or atypical environmental perturbations.