Intraspecific divergence of ionoregulatory physiology in the euryhaline teleost Fundulus heteroclitus: possible mechanisms of freshwater adaptation

We examined intraspecific variation in ionoregulatory physiology within euryhaline killifish, Fundulus heteroclitus, to understand possible mechanisms of freshwater adaptation in fish. Pronounced differences in freshwater tolerance existed between northern (2% mortality) and southern (19% mortality) killifish populations after transfer from brackish water (10 g l(-1)) to freshwater. Differences in Na(+) regulation between each population might …