Metabolic response of fishes when coping with temperature fluctuation: Thermal adaptation of salmonids

Abstract

Body temperature has a profound influence on animal activity through its thermodynamic effects on metabolism. The body temperature of ectotherms depends on the external temperature environment and, in contrast to the autonomous thermoregulation of endotherms, ectotherms adjust their body temperature using behavioral responses. Although behavioral thermoregulation is useful against daily temperature variations, it is not capable of coping with seasonal or annual temperature fluctuations. Under temperature fluctuations, ectotherms adjust their thermal sensitivities through plastic and/or genetic physiological changes. In the present review, salmonids are introduced as examples of the thermal adaptations of ectotherms. Most salmonids show strong fidelity to their natal streams for spawning, and this fidelity has resulted in genetically and geographically distinct populations within species. Salmonids are generally recognized as stenothermic and cold-adapted fishes but the temperature environments experienced by different populations are diverse. Indeed, it has been shown that in some salmonid species each population becomes locally adapted through the alteration of metabolic traits. I will review the thermal adaptation of fishes based on studies that clarify the links between the thermal performance of metabolic traits and environmental temperature in salmonids.