Consequences of circadian fluctuations in water temperature on the standard metabolic rate of Atlantic salmon parr (Salmo salar)

Abstract

Fish that inhabit rivers may experience important daily fluctuations in water temperature. Bioenergetic models have the potential to simulate the effects of such fluctuations on fish growth; however, bioenergetic components are traditionally modeled using fish kept at constant water temperatures. This study tested the hypothesis that circadian fluctuations in water temperature increase the standard metabolic rate of fish. The standard metabolic rate of Atlantic salmon parr (Salmo salar; 5.96–36.20 g wet blotted mass) estimated at 20 ± 0.5 °C was 25% to 32% lower for fish held at a relatively constant water temperature (20.2 ± 0.5 °C) than for fish maintained under fluctuating thermal regimes (19.8 ± 2.0 °C; 19.5 ± 3.0 °C). This study suggests that a rise in standard metabolic rate may explain how temperature fluctuations affect fish growth. It also indicates that the traditional approach used to estimate and model components of the bioenergetic equation may substantially underestimate the standard metabolic rate of fish that are subjected to such fluctuations.