Effects of low pH exposure on the osmo-respiratory compromise in banded killifish (Fundulus diaphanus)

Abstract

Low pH affects freshwater fish in several ways, with the effects on gas exchange and ion regulation being particularly important. These processes are connected through the osmo-respiratory compromise, the trade-off between gas exchange and ion regulation. Exercise exacerbates this trade-off, and low pH may further amplify these effects. This study explored the osmo-respiratory compromise in the acid-tolerant banded killifish (Fundulus diaphanus). Fish were acclimated to pH 7 (control) and pH 5 for 14 d and then subjected to trials measuring Na+ net flux and oxygen consumption rate (MO₂) following exhaustive exercise. I tested the hypothesis that low pH would exacerbate ion loss following chase, in accordance with the osmo-respiratory compromise. Contrary to expectations, fish acclimated to low pH exhibited more positive Na+ net flux rates and showed no reduction in aerobic capacity. These results suggest that banded killifish can quickly acclimate to low pH conditions, maintaining Na+ regulation and aerobic scope.