Cardiac mitochondrial plasticity and thermal sensitivity in a fish inhabiting an artificially heated ecosystem

Some evidence suggests that cardiac mitochondrial functions might be involved in the resilience of ectotherms such as fish to environmental warming. Here, we investigated the effects of acute and chronic changes in thermal regimes on cardiac mitochondrial plasticity and thermal sensitivity in perch (Perca fluviatilis) from an artificially heated ecosystem; the "Biotest enclosure" (similar to 25 degrees C), and from an adjacent area in the Baltic Sea with normal temperatures (reference, similar to 16 degrees C). We evaluated cardiac mitochondrial respiration at assay temperatures of 16 and 25 degrees C, as well as activities of lactate dehydrogenase (LDH) and citrate synthase (CS) in Biotest and reference perch following 8 months laboratory-acclimation to either 16 or 25 degrees C. While both populations exhibited higher acute mitochondrial thermal sensitivity when acclimated to their natural habitat temperatures, this sensitivity was lost when Biotest and reference fish were acclimated to 16 and 25 degrees C, respectively. Moreover, reference fish displayed patterns of metabolic thermal compensation when acclimated to 25 degrees C, whereas no changes were observed in Biotest perch acclimated to 16 degrees C, suggesting that cardiac mitochondrial metabolism of Biotest fish expresses local adaptation. This study highlights the adaptive responses of cardiac mitochondria to environmental warming, which can impact on fish survival and distribution in a warming climate.