Springer Online Journal Archives 1860-2000
Summary Wild populations of white suckers (Catostomus commersoni) were exposed to a fluctuating ambient pH regime (pH 7 to 4 to 7 to 4) in natural soft water. Blood and muscle ionic composition together with the net flux rate of acid-base equivalents, other ion transfers as well as unidirectional Na+ and Cl− exchanges were measured simultaneously in intact fish. Exposure to a shift in water pH from 7 to 4 for 12 h resulted in a marked net influx of both H+ (or loss of base) and SO 4 2− concomitant with net losses of other major body ions (Na+, Cl−, K+, Ca2+, Mg2+) as well as inhibition of gill NaCl influx and stimulation of gill diffusional efflux, depressed plasma ion levels (Na+, Cl−, Ca2+) and epaxial white muscle intracellular ion loss (K+, Mg2+). These responses slowly reversed when the water pH was elevated back to pH 7 for 12 h. Complete recovery was not achieved for some variables, however, even by 48 h. The responses upon re-exposure to water pH 4 for 12 h paralleled those seen during the initial acid exposure period, indicating that the introduction of a short period of neutral pH between two periods of acid exposure, was not ameliorative. Exposure to a fluctuating ambient pH regime, therefore, seemed to be more detrimental to the fish than continued, gradual or prior acid exposure. A regression analysis was performed on the ion transfer rates measured simultaneously in individual fish over the fluctuating pH regime. The results showed that exchange diffusion appears to be an important mechanism of NaCl transfer in white suckers and that the net flux rate of acid/base equivalents via the gill is closely correlated with the difference between all major cation (Na+, K+, Ca2+, Mg2+) and anion (Cl−, SO 4 2− ) net transfer rates.
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