The effect of pH on plasma electrolytes, carbonic anhydrase and ATPase activities in rainbow trout ( Salmo gairdnerii) and largescale suckers ( Catostomus macrocheilus)

Abstract

1. 1. Rainbow trout ( Salmo gairdnerii) and largescale suckers ( Catostomus macrocheilus) were exposed to water at pH 4.9, 5.6, 6.8 and 6.2 (control) for 21 and 14 days respectively. 2. 2. Changes in plasma electrolytes and activities of blood and gill carbonic anydrase and various ATPase enzymes in selected tissues were measured. 3. 3. Plasma Na +, K +, Cl −1 and osmolality in trout exposed to low pH increased in 2–7 days and decreased to less than control levels by 21 days. Mg 2+ and Ca 2+ in trout plasma showed little change. 4. 4. Increases in trout Na +-K +-, Na +-NH + 4- and HCO − 3 -ATPase activity, in gill tissue and carbonic anhydrase activity, in gill and blood of trout exposed to lower pH, suggested some compensation for electrolyte losses or imbalances. 5. 5. Suckers lost plasma ions (Na +, Cl −1, Ca 2+) and osmolality was reduced, at a low pH, to a greater extent than trout. 6. 6. At reduced pH Ca 2+-ATPase and HCO 3 −-ATPase enzyme activities were lower in suckers, whereas the increases in Na +-K +-ATPase, Na +-NH 4 +-ATPase and blood carbonic anhydrase did not increase as much as in trout. 7. 7. Trout thus appear to regulate plasma ion levels to a greater extent than suckers. That might indicate a basis for differential rates of disappearance of these species from acidified environments.