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

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Abstract
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+, Ca2+, and Mg2+ 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+, Ca2+, and Mg2+. 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 ENa+ decreased but ECl− remained unchanged. EK+ was correlated with plasma hyperkalemia. No changes in plasma levels or excretion of Ca2+ or Mg2+ 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.

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