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. Mg²⁺ and Ca²⁺ 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, Ca²⁺) and osmolality was reduced, at a low pH, to a greater extent than trout.

• 6.

  6. At reduced pH Ca²⁺-ATPase and HCO₃⁻-ATPase enzyme activities were lower in suckers, whereas the increases in Na⁺-K⁺-ATPase, Na⁺-NH₄⁺-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.