Branchial Sodium-Potassium ATPase Activity and Growth of Rainbow Trout in Seawater

Abstract

Changes in branchial Na-K ATPase activity and growth in two size groups of rainbow trout (Salmo gairdneri) – small with initial mean weight of 17.9 g and fork length of 11.9 cm and large, with an initial mean weight of 55.4 g and fork length of 17.2 cm – were investigated to determine if failure of small trout to adapt to salinity increases was due to low gill ATPase activity during seawater acclimation and culture in an estuary of Prince Edward Island. Increases in ATPase activity in the smaller trout followed salinity increases and were not significantly different from those of the larger trout. Growth rates for the smaller trout were not different from those for the larger trout, and were correlated with ATPase levels over 24 µMol P_i/mg protein per hour. ATPase levels were not affected by seawater temperatures above 15°C in July and August.