LI, T.*; ROER, R.D.: Effect of salinity on gill Na⁺, K⁺-ATPase activity in juvenile and adult Callinectes sapidus

Juvenile and adult blue crabs, Callinectes sapidus, were collected from Cape Fear River and acclimated in the laboratory for two weeks to either sea water (1050 mOsm) or dilute sea water (150 mOsm). Gills were removed from crabs, homogenized, and assayed biochemically for Na⁺, K⁺-ATPase activity. For adult crabs, individual anterior and posterior gills were assayed individually. For juveniles, anterior gills from individual crabs were pooled, as were posterior gills. Both anterior and posterior gills were also fixed and prepared for transmission electron and light microscopy. Gills from adult crabs acclimated to sea water showed low levels of Na⁺, K⁺-ATPase activity, although the posterior gills had twice that of anterior gills. Juvenile crabs (<5g in weight) had enzyme levels 11 times higher than those in the anterior gills of adults and 7.5 times higher in posterior gills in sea water. Upon acclimation to 150 mOsm, adult anterior gills displayed a 3-fold increase in Na⁺, K⁺-ATPase activity; posterior gills had a 4.3-fold increase. In contrast, the anterior gills of juvenile crabs had a 4.3-fold increase, while the posterior gills demonstrated an 11-fold increase relative to sea water. Specific activity of Na⁺, K⁺-ATPase in juvenile gills at 150 mOsm was 15 times and 19 times higher than that of anterior and posterior gills of adults, respectively. Preliminary microscopic examination of anterior gills from 150 mOsm-acclimated juvenile crabs failed to reveal morphology typical of the transport epithelium of posterior gills.