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Journal of Experimental Biology 133,183-197 (1987)
Published by Company of Biologists 1987

Compensation of Progressive Hypercapnia in Channel Catfish and Blue Crabs

JAMES N. CAMERON ¹ and GEORGE K. IWAMA ¹

¹ Departments of Zoology and Marine Studies, The University of Texas Marine Science Institute Port Aransas, TX 78373, USA

Channel catfish (Ictalurus punctatus Rafinesque) were progressively acclimated to CO₂ partial pressures of 7.5, 15, 30, 45 and 58 mmHg (1, 2, 4, 6 and 8% CO₂ in air) and blue crabs (Callinectes sapidus Rathbun) to 15, 30 and 45 mmHg, with 24 h at each partial pressure. Measurements of both conventional acid-base parameters (pH, P_CO2. total CO₂) and ‘strong’ ion concentrations (Na⁺, K⁺, Mg²⁺, Ca²⁺ and Cl^-) were made at various times during each treatment. Intracellular [Na⁺], [K⁺] and [Cl^-] were determined for red and white muscle in control and hypercapnic (8%) catfish. Extracellular [HCO₃^-] and strong ion difference (SID) both rose during hypercapnic compensation, with correlation coefficients (r) of 0.97 (P<0.01) for catfish and 0.41 (NS) for blue crabs. Since [HCO₃^-] is calculated from two rapid measurements, and SID from four separate procedures, the former appears to be the measurement of choice. The results also dispel the notion of a 30 mequiv1^-1 upper limit to bicarbonate compensation: [HCO₃^-] values over 50mequiv1^-1 were achieved in both animals, and %pH regulation remained around 70% at the highest P_CO2 Due to superior intracellular buffering, the large change in extracellular SID did not lead to a measurable change in the concentrations of the major intracellular ions. The primary gill filaments of hypercapnic catfish showed a 30% increase in numbers and a 75% increase in area of apical crypts of chloride cells. The chloride cell ‘patches’ in crab gills increased in staining density after hypercapnia but did not enlarge.

Note:

Present address: Department of Biology, Dalhousie University, Halifax, NS, Canada B3H4JI.

Key words: acid-base, fish, hypercapnia, electrolyte.

Accepted on June 24, 1987

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