Lentic waters of the Gulf-Atlantic Coastal Plain include some of the most acidic environments found in subtropical latitudes. Fishes of this ecoregion have adapted to life in hyperthermal, hypoxic, and hyperacidic conditions, and natural selection may have influenced the physiology of independent lineages in a similar fashion. We are examining the evolution of the Electron Transport Chain to assess the functional consequences of extraordinary mtDNA variation observed in certain lentic fishes of the GACP>