Physiological Evidence of Acclimation to Acid/Aluminum Stress in Adult Brook Trout (Salvelinus fontinalis). 1. Blood Composition and Net Sodium Fluxes

Abstract

Brook trout (Salvelinus fontinalis) adapt to chronic sublethal acid/Al stress. The accompanying acclimiation confers greater resistance to short-term increases in Al and acidity. Adult trout were exposed in flowing soft water to eight combinations of pH (6.5, 5.2) .times. Ca2+ (25, 400 .mu.equiv/L) .times. Al (0, 75, 150 .mu.g/L=0, 2.8, 5.6 .mu.mol/L). After 10 wk, blood sampling by caudal puncture revealed no significant variations in osmolality, plasma protein, or hemoglobin and only minor differences (.ltoreq.15%) in plasma Na+ and Cl-. Overall, most electrolytes were higher in fish exposed to higher water Al and/or Ca2+; only plasma Ca2+ was directly depressed by low pH. Hematocrit was raised by both low pH and elevated Al. When trout naive to both acid and Al were challenged with pH=4.8, Al=333 .mu.g/L under flow-through conditions, there were large negative whole-body Na+ fluxes and marked depressions of plasma Na+ and Cl-, hemoconcentration, and substantial mortality over 48 h. Prior exposure for 10 wk to pH = 5.2 plus either 75 or 150 .mu.g Al/L prevented mortality and ameliorated or abolished these effects through a more rapid recovery of net Na+ balance. Prior exposure to pH=5.2 alone ameliorated these effects only slightly.