| Summary: | Fish provide some of the best-studied examples of marked intraspecific variation in metabolic rate: after accounting for variation in size and age, there can typically be a 2-3 fold variation among individual fish for both standard and maximum metabolic rate (SMR and MMR), and also in their aerobic scope (AS, the difference between SMR and MMR and hence a fish’s capacity to increase its aerobic metabolism). These differences are relatively stable over time, although individual fish differ in the extent to which they can alter their metabolism when environmental conditions change. In this presentation I will briefly consider the extent and causes of individual variation in SMR, MMR and AS, considering both the mechanistic basis (e.g. individual variation in mitochondrial performance) and its origins, including a consideration of genetic and maternal effects. I will then describe both documented and potential links between metabolism, behaviour and performance. Intraspecific variation in metabolism has been found to be related to other traits. As an example, fish with a relatively high SMR tend to be more dominant, digest food faster and grow faster than those with a low SMR, but these advantages only apply in environments where the food supply is high and predictable; in less favourable environments they lose their advantage, and are more prone to risk-taking when conditions deteriorate. Less is known about the ecological consequences of individual variation in MMR and AS, although fish with a higher AS are known to have advantages in some contexts. This is especially important in the context of climate change, since it has been suggested that constraints on AS may underlie the poor performance of fishes at higher temperatures. Given these links between metabolism and measures of performance, understanding the metabolic responses of individuals to changing environments will be a key area for future research.
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