Limited adaptation to non-natal osmotic environments at high water temperature in euryhaline wanderer fishes

Gradual transfer experiments were conducted to see whether Japanese dace Tribolodon hakonensis (freshwater species) and Japanese black porgy Acanthopagrus schlegelii (marine species) could acclimate to high and low temperatures in natal and non-natal osmotic environments. Two groups of each species, one acclimated to their natal osmotic environment and the other to a non-natal osmotic environment, were exposed to gradual temperature changes. Under high temperature conditions, the plasma osmolality (Posm) of both species approached the osmolality of ambient water, and high mortality was observed in the non-natal osmotic environments but not in the natal osmotic environments. In contrast, there was no clear evidence that the osmoregulatory capacity of either species had declined under low temperature conditions in the natal and non-natal osmotic environments. Limited adaptation of these fishes to non-natal osmotic environments at high temperature suggests that global warming may impair their entry to non-natal habitats.