Mitochondrial oxidative phosphorylation genes play critical role in energy metabolism, aerobic potential and thermogenesis. These genes were thought to evolve neutrally, however increasing evidence suggests that mitogenome is susceptible to selection and adaptive variation. Organisms that have encountered selective forces to improve their metabolic potential or adapt to cooler environment can be suitable candidates to study the pattern and impact of selection on mitochondrial genome. Tunas, billfishes, butterfly mackerel and opah are the only teleost fishes to exhibit regional endothermy. They might have experienced strong selective forces to enhance their metabolic potential making them a suitable candidate group to search for positive selection. Mitochondrial protein coding genes of 16 regionally endothermic teleosts retrieved from NCBI GenBank were used to examine the pattern of selection using different ω-based approaches implemented in DATAMONKEY and TreeSAAP to analyze the changes in physicochemical properties of the amino acids. We found evidence for positive selection in different mitochondrial protein subunits across several branches of the phylogeny. Changes found in the subunits ND5 and ND6 might have modified the proton pumping efficiency and assembly of complex I respectively and the substitutions found in the subunit ATP6 might have an impact on the rotor performance of the complex V. Further studies on assessment of metabolic consequences of OXPHOS substitutions are essential to understand the importance of these substitutions on the performance of the fishes

Positive selection, regional endothermy, mitochondrial genome, oxidative phosphorylation (OXPHOS), adaptive variation