Common carp Cyprinus carpio were fed at a constant feeding rate for 30 days on isoenergetic diets containing different levels of carbohydrate (4-58%) and protein (65-27%), and activities of several hepatopancreatic enzymes together with growth performance were determined. Dietary inclusion of adequate levels of carbohydrate improved the growth and feed conversion and exerted a protein-spar ing effect. With increasing dietary carbohydrate levels and decreasing protein levels, the activities of hepatopancreatic glucosephosphate isomerase, glucose-6-phosphate and phosphogluconate de hydrogenases, and malic enzyme as well as hepatopancreatic glycogen and serum triglyceride contents increased, while those of glucose-6-phosphatase, arginase, GOT, and GPT together with serum free amino acid concentrations decreased. Therefore, high correlation coefficients were obtained between dietary carbohydrate levels and these biochemical parameter concentrations. The results suggest that dietary carbohydrate stimulates glycolysis and lipogenesis and depresses gluconeogenesis and amino acid degradation in the hepatopancreas. This comprehensive regulation of nutrient metabolism may ac count for the protein-sparing effect exerted by dietary carbohydrate.
Common carp Cyprinus carpio were fed a commercial diet for 30 days at different feeding rates (100, 90, 80, 70, 50, 30, and 0% of satiation), and the activities of hepatopancreatic enzymes and body composition were determined. It is well known that dietary composition and starvation affect body composition and enzyme activities in various fishes, and the authors have reported in previous papers1-4) that the activities of glycolytic and lipogenic enzymes in the livers of yellowtail and carp decreased not only with decreases in dietary carbohydrate but also with starvation and decreases in feed intake in winter. In the natural environment, most fish species con front various kinds of feed restrictions caused by seasonal fluctuations in food supply or by de creases in water temperature.However, there is limited information on the effect of feed restriction on the nutrient metabolism in fish.5)In the present study, carp were fed a diet at dif ferent feeding rates for 30 days, and the activities of hepatopancreatic enzymes relating to glycoly sis, gluconeogenesis, lipogenesis, and amino acid degradation and the contents of constitutents in the serum, hepatopancreas, and whole body were determined.From the results, metabolic re sponse to feed restriction is discussed.
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