ENZYME-ACTIVITIES OF GILL, HEPATOPANCREAS, MANTLE, AND ADDUCTOR MUSCLE OF THE OYSTER (CRASSOSTREA-VIRGINICA) AFTER CHANGES IN DIET AND SALINITY

We examined the effects of exposure to low salinity (1/3 seawater) on the maximal activities of enzymes of lipid oxidation, amino acid and ketone body metabolism, gluconeogenesis, and glycolysis in gill, mantle, hepato-pancreas, and adductor muscle of the oyster (Crassostrea virginica). No significant metabolic reorganization occurred after 4-6 wk in low salinity. The few significant differences which were found between enzyme activities of high- and low-salinity treatment groups were always due to lower activities in the low-salinity group. In particular, hexokinase, fructose bisphosphatase, and 3-hydroxyacyl CoA dehydrogenase declined in gill, hepato-pancreas, and adductor muscle. Since high ionic strength depresses the activity of many enzymes, the reduced ionic strength in the cells of the low-salinity group may perturb metabolism by elevating rates of enzyme activity. As indicated by the present study, part of the response to low salinity by euryhaline molluscs may involve reducing the activity of certain enzymes to achieve a homeostasis of metabolic function.