Cl−, K+, and acid–base balance in rainbow trout during exposure to, and recovery from, sublethal environmental acidification

Abstract

A review of pertinent literature is provided. Previous research showed that fish exposed to sublethal environmental acidification have reduced blood pH, plasma [HCO₃⁻], and [Cl⁻] and increased plasma [K⁺]. Simultaneous sampling from blood and water was used to characterize changes in Cl⁻, K⁺, and acid–base regulation in rainbow trout during a 5-day exposure to pH 4 followed by a 24-h recovery period at pH 7. At pH 4, there was a continuous loss of Cl⁻ (49.8 μmol/kg per hour), and K⁺ (23.0 μmol/kg per hour) to the water. Blood ion concentrations did not change in a corresponding manner. Blood pH and plasma [HCO₃⁻] decreased continuously owing to a net uptake of acid from the water. Recovery at pH 7 involved uptake of Cl⁻ from, and loss of K⁺ to, the water. Plasma [K⁺] returned to normal but there was no significant change in plasma [Cl⁻] during this 24-h period. Internal acid–base parameters recovered much more quickly owing to a net excretion of acid into the water. The more rapid recovery of acid–base balance suggests that branchial acid–base and ionoregulatory mechanisms may be only loosely linked. The irregular changes in blood ion concentrations indicate that considerable ionic and osmotic exchanges between the plasma, the remainder of the extracellular space, and the intracellular space must result from exposure to pH 4.