EFFECTS OF ENVIRONMENTAL ALKALINITY ON CALCIUM-STIMULATED DEPHOSPHORYLATING ENZYME-ACTIVITY IN THE GILLS OF POSTMOLT AND INTERMOLT GIANT FRESH-WATER PRAWNS MACROBRACHIUM-ROSENBERGII (DE MAN)

Evidence of calcium-stimulated dephosphorylating enzyme activity was f ound in the gills of the giant freshwater prawn Macrobrachium rosenber gii. The activity of the enzyme was influenced by environmental alkali nity. Branchial enzyme activity was measured in postmoult and intermou lt prawns exposed to low (25 mg/l) and high (250 mg/l) alkalinity wate rs maintained at 20 mg/l total hardness. At low environmental alkalini ty, the enzyme activity was higher in postmoult (2.11 mu mol Pi mg/pro tein/hr) than in intermoult prawns (0.58 mu mol Pi mg/protein/hr) whil e at high alkalinity enzyme activity was equally high in both postmoul t and intermoult prawns (1.29 and 1.30 mu mol Pi mg/protein/hr respect ively). The activity in postmoult prawns did not differ significantly at the low and high alkalinities.