Long-term sublethal acid exposure in rainbow trout (Salmo gairdneri) in soft water: effects on ion exchanges and blood chemistry

Long-term sublethal acid exposure (3 mo, pH 4.8) in adult rainbow trout acclimated to soft water caused transient net losses 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 Ca²⁺ 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. Despite stabilization at a new steady state, rainbow trout were physiologically affected in a deleterious manner by chronic sublethal acid exposure in soft water. -from Authors