The Maximum Power Principle in Behavioral Thermoregulation by Fishes

The maximum power principle suggests that successful biological systems maximize the flow of useful energy. Using this principle in conjunction with Fryˈs metabolic scope concept, we have developed a model of behavioral thermoregulation for fishes that reasonably predicts frequency distributions and swimming speeds of fish in thermal gradients: fish respond to temperature gradients by swimming at speeds that are proportional to the rate of change of metabolic scope with respect to temperature. As a result, reduced thermoregulatory swimming power occurs at temperatures that give higher levels of metabolic scope; this maximizes both available surplus power and residence time under conditions of high surplus power availability. Within the zone of high residence time (=preferred temperature zone), fish respond to changes in the gradient of metabolic scope with increased turning, thus increasing their frequency of occurrence near the temperature that permits maximum metabolic scope.