Contrasting effects of temperature acclimation on mechanisms of ionic regulation in a eurythermic and a stenothermic species of freshwater fish ( Rutilus rutilus and salvelinus alpinus)

Abstract

1. 1. Effects of temperature on aspects of ionic regulation in kidney and gills of Rutilus rutilus and Salvelinus alpinus were studied by a variety of techniques. 2. 2. In the kidney tissue of cold acclimated R. rutilus, the maximal number of binding sites per mg protein (Bmax) and the activity of Na +, K +-ATPase, as well as tissue respiration increased significantly, whereas in S. alpinus no changes in these variables were observed. On the other hand, 86Rb + efflux from kidney tissue was unaffected by temperature in R. rutilus, whereas it was about 60% lower in 5. alpinus acclimated and measured at 5°C, than in specimens acclimated and measured at 15°C. 3. 3. In both species, the activity of gill Na +, K +-ATPase was 1.5- to 2-fold higher in cold-acclimated than in warm-acclimated fish although Bmax decreased in R. rutilus, but remained constant in S. alpinus. 4. 4. Problems of ionic regulation are discussed with regard to differences in temperature sensitivity of passive flows and primary active transport of ions in the tissues of poikilothermic animals.