Sodium Transport In the Brook Trout,Salvelinus fontinalis: Effects of Prolonged Low pH Exposure in the Presence and Absence of Aluminum

Abstract

This study examined the effects of prolonged exposure (.gtoreq.10 wk) to low Ca2+ (25 versus 400 .mu.equiv/L), low pH (pH 5.2 versus 6.5) with and without Al (150 .mu.g/L) on Na+ uptake in adult brook trout (Salvelinus fontinalis). Na+ uptake (JinNa+) was assessed by measuring radiotracer disappearance from the medium at ambient Na+ (79 .mu.equiv/L) and in response to acute increases in ambient Na+. The relationship between JinNa+ and [Na+] was best described by a linear model with the slope of the line a measure of transport activity. Transport activity increased as a result of prolonged low Ca2+ exposure at pH 6.5, but declined in fish maintained at pH 5.2. These fish showed no compensation in response to low pH; there was no recovery in transport activity when pH was acutely raised to 6.5, and lower pH''s further inhibited uptake. In contrast, the Na+ transport activity of fish maintained at pH 5.2 and 150 .mu.g Al/L was significantly greater than that of fish acclimated to pH 5.2 alone and indeed greater than pH 6.5 controls. This indicates that Al exposure induced a compensatory mechanism in the gills that was not seen with low pH exposure alone.