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Journal of Experimental Biology 121,77-94 (1986)
Published by Company of Biologists 1986

Responses of a Stenohaline Freshwater Teleost (Catostomus Commersoni) to Hypersaline Exposure : I. The Dependence of Plasma pH and Bicarbonate Concentration on Electrolyte Regulation

P. R. H. WILKES ¹ and B. R. MCMAHON ²

¹ Department of Biology, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada; Department of Internal Medicine, Health Sciences Centre, University of Calgary, Calgary, Alberta T2N 1N4, Canada
² Department of Biology, University of Calgary, 2500 University Drive NW, Calgary, Alberta T2N 1N4, Canada

The effects of exposure to 0.94% (300 mosmol1^-1) sodium chloride on plasma electrolyte and acid-base status were examined in the freshwater stenohaline teleost Catostomus commersoni (Lacépède), the white sucker. Four days' exposure to this maximum sublethal salinity resulted in an increase in plasma concentrations of both sodium and chloride but a decrease in the Na⁺/Cl^- ratio. Since the plasma concentrations of free amino acids and other strong ions - Ca²⁺, Mg²⁺ and K⁺ - remained unchanged, plasma strong ion difference (SID) decreased. Additionally, plasma pH and bicarbonate concentration decreased at constant P_coco2 The changes in electrolyte and acid-base status that occurred after the 96 h were not appreciably altered after a further 2-3 weeks of saline exposure. The ambient calcium concentration had no influence on these results.

Haemolymph non-bicarbonate buffer capacity () calculated as [HCO₃^-]/ pH, increased in saline-exposed fish. Consequently H⁺, the apparent proton load, was zero despite the apparent change in acid-base status. Although was directly proportional to the haemoglobin concentration in both control and experimental fish, this could not account for the increase in since haemoglobin remained at control values. These results can be explained solely by the change in plasma SID and serve to illustrate the dependence of plasma acid-base status on the prevailing electrolyte characteristics, weak acid concentration and P_coco2.

Key words: electrolyte, acid-base, strong ion difference

Accepted on October 11, 1985