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Journal of Experimental Biology 113,237-252 (1984)
Published by Company of Biologists 1984

Whole Body Calcium Flux Rates in Freshwater Teleosts as a Function of Ambient Calcium and pH Levels: a Comparison Between the Euryhaline Trout, Salmo Gairdneri and Stenohaline Bullhead, Ictalurus Nebulosus

HELVE HBE ¹, PIERRE LAURENT ², and BRIAN R. MCMAHON ³

¹ Laboratoire de Morphologie fonctionnelle et ultrastructurale des adaptations, Centre National de la Recherche Scientifique, 23 Rue de Loess, Strasbourg, Cronenbourg 67037 France.; Department of Biology, Lakehead University, Thunder Bay, Ontario, Canada P7B 5EI.
² Laboratoire de Morphologie fonctionnelle et ultrastructurale des adaptations, Centre National de la Recherche Scientifique, 23 Rue de Loess, Strasbourg, Cronenbourg 67037 France
³ Department of Biology, University of Calgary, Calgary, Alberta T2N 1N4, Canada

The exchange of calcium between the blood and external medium following intravascular injection of ⁴⁵Ca was investigated in adult fresh water rainbowtrout (Salmogairdneri) acclimated to ambient [Ca²⁺] of 0.18, 0.65 and 5.0 mequivl^-1, and in bull heads (Ictalurus nebulosus) at external [Ca²⁺] of 0.17 mequivl^-1, each at near-neutral ambient pH, 11-12°C and constant Na⁺ and Cl^- levels of 0.06 and 0.03 mequivl^-1, respectively.

The dispersal volume of isotope exhibited a slow exponential increase with 8-9 h required for 95% of the radiospace to be filled, irrespective ofthe acclimation medium or fish species. Equilibrium radiospaces in trout (range 1600-2000 ml kg^-1) were independent of ambient [Ca²⁺] but 1.4 -fold higher than in bullheads. In all cases, whole body exchangeable calciumcontent was low, representing 3 % of total body calcium content. The whole body calcium exchange rates (mean ranges; influx or efflux) in trout of 7-22µequiv kg^-1 h^-1 were largely independent of ambient Ca²⁺ levels; lower values of 2-10µequiv kg^-1 h were found in bullheads.

Acute exposure (24 h) to low ambient pH 4.0-4.2 at external [Ca²⁺] 0.18 mequivl^-1 resulted in whole body ion loss in both species. Net Ca²⁺ losses in trout were due to a reduction in influx whereas both increased efflux and depressed influx accounted for the response in bullheads. These changes were transitory (12 h) and minor in comparison with concomitantnet Na⁺ and Cl^- losses which unlike Ca²⁺, exhibited no recovery within 24 h of acid exposure.

Possible mechanisms of Ca²⁺ regulation in fresh water fish are discussed.

Key words: Fish, calcium, radiospaces, unidirectional exchanges, low pH

Accepted on May 9, 1984

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