Energetics of locomotion in warm-bodied fish.

Most fishes are poikilothermic-Le. their body temperature is within a few degrees of ambient unless ambient is changing rapidly. The exceptions are certain sharks and true tunas. Little is known about the locomotion and energetics of warm-bodied sharks. Our review focuses on a few species of tunas but draws on information from other fish (especially salmonids) to fill in the gaps in our understanding. Of interest here is a measure of the metabolic cost of producing known amounts of work per unit time; but there are problems with both sides of this equation, especially in the aquatic environment. Webb (30) has used a scheme similar to that in Figure 1 to show how total metabolic costs are partitioned. Since this approach is appropriate for sustained swimming in steady-state (i.e. oxygen supply keeping up with demand), especially when experiments are performed for short periods (hours), it is used here. Energy input or metabolic cost has been successfully estimated by measuring oxygen uptake and calories ingested. We focus our discussion on estimates based on these measurements. Other techniques for measuring metabolic costs have either been tried unsuccessfully or are yet to be tried. For example, few measurements have been made of C 0 2 production in fish (15, 16) and none for tuna. Knowledge of heat exchange rates and excess temperature has permitted some specula-