Long-Term Sublethal Acid Exposure in Rainbow Trout (<i>Salmo gairdneri</i>) in Soft Water: Effects on Ion Exchanges and Blood Chemistry

Abstract

Long-term sublethal acid exposure (3 mo, pH 4.8) in adult rainbow trout (Salmo gairdneri) acclimated to artificial soft water (Ca 2+ = 50, Na + = 50, Cl − = 100 μeq∙L −1 ) caused transient net fosses of Na + and Cl − . Net flux rates of both ions were returned to control levels after 30–52 d of acid exposure through a new equilibrium between unidirectional influx and efflux, where both were lower than control rates. K + balance remained negative and Ca 2+ balance at zero throughout the exposure. No changes in net acidic equivalent flux occurred, indicating the absence of acid–base disturbance, but ammonia excretion increased over time. Muscle K + , Na + , and Cl − fell and Ca 2+ increased. Plasma Na + , Cl − , and osmolality decreased, while plasma protein, glucose, and blood hemoglobin increased during the first few weeks of acid exposure. Plasma K + and Ca 2+ did not change. General stabilization of plasma parameters occurred in concert with the stabilization of Na + and Cl − flux rates, but no recovery to control levels was observed for any of them. We conclude that despite this stabilization at a new steady state, rainbow trout were physiologically affected in a deleterious manner by chronic sublethal acid exposure in soft water.