HEAD, J.M.*; PEQUEUX, A.: Salinity and temperature effects on Na+/K+-ATPase and cytochrome c oxidase activity in the gills of Eriocheir sinensis.

Eriocheir sinensis is exposed to wide variations in temperature and salinity. The effects that they have on the gill function of E. sinensis play a major role in determining the crab’s distribution and success. The enzymatic activity of Na+/K+-ATPase indicates the degree of osmoregulation in the gills, while the activity of cytochrome c oxidase (COX) reflects oxidative activity. Crabs were acclimated for two weeks at three temperatures (5°,15°,and 25°C) in either fresh or salt water. Na+/K+-ATPase and COX activity of the anterior and posterior gills were measured spectrophotometrically. In FW crabs, Na+/K+-ATPase activity in posterior gills was always significantly higher than that of anterior gills. Activity was inversely related to acclimation temperature. In SW crabs, activity was significantly more elevated in the posterior gills at 5°C and 15°C compared to the anterior gills. Activity in the posterior gills was significantly higher at 5°C compared to 15°C and 25°C. Posterior gills of FW crabs always had significantly higher Na+/K+-ATPase activity than SW crabs. COX activity was significantly higher: in the posterior gills of all groups, in FW crabs compared to SW crabs, and at lower temperatures. Increases in Na+/K+-ATPase activity seen in FW crabs convey the need to actively pump ions across respiratory surfaces in FW. The lower activity of anterior gills reflects their more respiratory function. As pumping ions is an oxidative process, COX activity increases in FW crabs and in the posterior gills. The effect of temperature on the enzymatic activity of the gills suggests thermocompensation after two weeks of acclimation. Supported by a Fulbright Grant to J.M. Head