Alternate feeding between high- and low- carbohydrate based diets improves the growth digestive capacity, liver glycometabolism for common carp (Cyprinus carpio)

Use of high-concentrate carbohydrate in fish diets will bring negative influence on the growth and glycometabolism. The current research, with common carp, was designed to investigate the efficiency of alternate feeding between high- and low- carbohydrate based diets in weakening these negative effects. Two control groups were, respectively, fed to the low carbohydrate diets (LC group, 100 g/kg cassava starch) and the high carbohydrate diets (HC group, 400 g/kg cassava starch) for 56 d, meanwhile other groups were subjected to every 1 d, 7 d, 14 d and 28 d alternation between the HC and LC diets, respectively (referred as R1, R7, R14 and R28). All experimental diets were fed to triplicate groups of 30 common carp (initial weight 1.17 +/- 0.03 g). All four alternate groups achieved optimal growth and feed efficiency compared to the HC group. The R14 group possessed significantly higher weight growth rate, protein efficiency ratio, specific growth rate, intestinal index and condition factor, and significantly lower feed conversion ratio compared to the HC group. Fish in that group had higher protein content in whole body, higher expressions of growth hormone and insulin-like growth factor 1 in hepatopancreas and elevated intestinal activities of trypsin, amylase and alkaline phosphatase. Relative expressions of rapamycin, phosphatidylinositol 3-kinase, protein kinase B, Forkhead frame protein 1 A/1B, hexokinase, pyruvate kinase, glucokinase, phosphofructokinase, glucose transporter 2, glucose transporter 4, and sodium glucose cotransporter were also enhanced in the R14 group compared to HC group. Additionally, there was no difference in growth parameters between the LC group and four alternate groups. Alternate feeding between different carbohydrate level diets could enhance the growth, improve the digestive capacity and strengthen the glycometabolism to heighten the utilization ability of fish to high-carbohydrate diets, but this alternate cycle should be within reasonable limits. Briefly, it was concluded that the alternate cycle of 14 d was best.