The Impact of Acclimation on Standard and Maximum Metabolic Rate in a Small Freshwater Fish

AbstractThe ability of freshwater fish to acclimate quickly to water temperature variation is imperative when living in shallow changeable environments. However, while it has often been assumed that maximum metabolic rate is constant and therefore that metabolic scope (the difference between maximum and standard metabolic rates) decreases with ambient temperature, this assumption is weakly supported and remains controversial. We investigated acclimation in a temperate, shallow-dwelling Australian freshwater fish, the Pacific blue-eye (<i>Pseudomugil signifer</i>), to rising water temperatures. We placed wild-caught fish into three acclimation treatments (24°C, 28°C, and 30°C) and measured metabolic rate at three test temperatures (24°C, 28°C, and 30°C). We found that fish acclimated (recovered standard metabolic rate) to housing temperatures before the first measurement at 10 d. Moreover, we found that regardless of acclimation temperature, standard metabolic rate, maximum metabolic rate, and aerobic scope all increased with test temperature. Our findings suggest that maximum metabolic rate and metabolic scope can adjust rapidly to ambient temperature. More research is needed to understand the generality of these effects, as well as their consequences for fitness.