Acid–base balance, ionic status, and renal function in resting and acid-exposed white suckers (Catostomus commersoni)

Renal function was investigated in the stenohaline Catostomus commersoni held at water pH 7.3 for 5 days. Urine displayed remarkably low levels of Na + , Cl − , K + , Ca 2+ , and Mg 2+ and was very acidic (mean pH 6.5). Renal electrolyte conservation was characterized by almost complete reabsorption of NaCl and to a lesser degree, K + , Ca 2+ , and Mg 2+ . Net H + excretion was + 11.2 μequiv∙kg −1 ∙h −1 , resulting primarily from a high titratable acid content. The physiological consequences of exposure to ambient pH 4.3 for 4 days included disturbances in plasma acid–base status with relatively minor changes in both plasma ion levels and renal output (E). A mixed metabolic and respiratory acidosis developed, which was not compensated for by increased renal H + excretion. Both plasma NaCl levels and E Na + decreased but E Cl − remained unchanged. E K + was correlated with plasma hyperkalemia. No changes in plasma levels or excretion of Ca 2+ or Mg 2+ occurred. These findings provide some physiological evidence supporting the contention that suckers are relatively acid tolerant. It is suggested that the copious amounts of mucus covering their gills may have served a protective role by retarding proton entry and limiting branchial ion loss.