Seasonal variations in carbohydrate-metabolizing enzyme activity and body composition of Japanese pearl oyster Pinctada fucata martensii in pearl culture

In order to investigate the seasonal variations of carbohydrate-metabolizin g enzyme activities and body compositions in the adductor muscle and intern al organ of Japanese pearl oyster Pinctada fucata martensii, the bivalve we re cultured from May 1996 to July 1997. The glycogen content in adductor mu scle varied seasonally with the accumulative quantity of phytopigment conce ntration in environmental water, and decreased with increases in the activi ties of phosphorylase, phosphofructokinase, and pyruvate kinase in the tiss ue from September to October. Thereafter, the glycogen content reached a po or level in November, when the activities of their glycolytic enzymes decre ased remarkably. The activity of glucose-6-phosphate dehydrogenase in inter nal organ coincided seasonally with reproductive cycle and the absolute qua ntity of crude fat in this tissue, suggesting the provision of NADPH for th e synthesis of fatty acids and sterols. These results suggested that the se asonal variations in carbohydrate-metabolizing enzyme activity and body com position of pearl oyster are influenced mainly by feed quantity and sexual maturity.