Branchial and Renal Acid and Ion Fluxes in the Rainbow Trout, Salmo Gairdneri, at Low Environmental pH

Abstract

Rainbow trout were exposed for 4 days to an environmental pH averaging 4.2, an exposure which resulted in a continuous net branchial influx of acid. The influx provoked a progressive depression in blood pH and [HCO₃⁻], virtually complete by 48 h, and a marked increase in renal acid excretion, also complete by 48 h. The increase in the latter was sufficient to remove, at maximum, about half of the protons entering at the gills; those remaining were buffered in body fluids. The low pH exposure also impaired gill ion regulation as indicated by continuous net branchial losses of Na⁺, Cl⁻ and K⁺ and by a progressive decline in plasma Na⁺ and Cl⁻ levels. Evidence is presented which indicates that there was a significant contribution by the intracellular compartment both to the total body ion losses and to the buffering of the body acid load.