Metabolic rate increases with thermal acclimation and is associated with mitochondrial function in some tissues of threespine stickleback

The metabolic rate (ṀO2) of eurythermal fishes changes in response to temperature, yet it is unclear how changes in mitochondrial function contribute to changes in ṀO2. We hypothesized that ṀO2 would increase with acclimation temperature in the threespine stickleback (Gasterosteus aculeatus) in parallel with metabolic remodeling at the cellular level but that changes in metabolism in some tissues and organs, such as liver, would contribute more to changes in ṀO2 than others. Threespine stickleback were acclimated to 5, 12 and 20°C for 21 weeks. At each temperature, standard and maximum metabolic rate (SMR and MMR, respectively), and aerobic scope (AS) were quantified, along with mitochondrial respiration rates in liver, oxidative skeletal, and cardiac muscles, and the maximal activity of citrate synthase (CS) and lactate dehydrogenase (LDH) in liver, and oxidative and glycolytic skeletal muscles. SMR, MMR and AS increased with acclimation temperature, along with rates of mitochondrial p...