Seasonal Variations of Carbohydrate-Metabolizing Enzyme Activity and Lipid Content in Carp Reared Indoors

Abstract

Carp, Cyprinus carpio, were fed to satiation with a commercial diet in an indoor aquarium for more than ten months, and seasonal changes of carbohydrate-metabolizing enzyme activities and general composition were investigated. Though the activity of glucose-6-phosphatase was nearly constant throughout the experimental period, those of glucosephosphate isomerase, fructose diphosphatase and aspartate aminotransferase were high in spring and summer and low in winter, reflecting changes of the food comsumption. On the other hand, activities of glucose-6-phosphate and phosphogluconate dehydrogenases in pentosephosphate cycle were increased in autumn and decreased in winter. These seasonal changes of the dehydrogenase activities coincided with those of the hepatopancreas and body fat contents, although the body fat increment was somewhat late. These changes suggest that decrease of environmental temperature in early autumn causes an activation of pentosephosphate cycle dehydrogenases to accelerate fatty acid synthesis in spite of a lowered feeding rate, resulting in marked accumulation of body fat. These results suggest that, in the poikilothermic animal, environmental temperature causes various and reasonable changes in the levels of carbohydrate-metabolizing enzymes and body components through changing their feeding rates.