Plasticity, repeatability and phenotypic correlations of aerobic metabolic traits in a small estuarine fish.

Standard metabolic rate (SMR), maximum metabolic rate (MMR), absolute aerobic scope (AAS) and critical oxygen tension () were determined for the Gulf killifish, , an ecologically dominant estuarine fish, acclimated to lowered salinity, elevated temperature and lowered oxygen concentration. Acclimation to low salinity resulted in a small, but significant, elevation of (suggesting lower tolerance of hypoxia); acclimation to elevated temperature increased SMR, MMR, AAS and ; acclimation to low oxygen led to a small increase in SMR, but substantial decreases in MMR, AAS and Variation in these metabolic traits among individuals was consistent and repeatable when measured during multiple control exposures over 7 months. Trait repeatability was unaffected by acclimation condition, suggesting that repeatability of these traits is not context dependent. There were significant phenotypic correlations between specific metabolic traits: SMR was positively correlated with MMR and ; MMR was positively correlated with AAS; and AAS was negatively correlated with In general, within-individual variation contributed more than among-individual variation to these phenotypic correlations. The effects of acclimation on these traits demonstrate that aerobic metabolism is plastic and influenced by the conditions experienced by these fish in the dynamic habitats in which they occur; however, the repeatability of these traits and the correlations among them suggest that these traits change in ways that maintain the rank order of performance among individuals across a range of environmental variation.