Adaptation of Chinese perch (Siniperca chuatsi) to different levels of dietary carbohydrates

The objective of the study was to investigate the effects of dietary carbohydrate on growth performance, feed utilization, proximate compositions, and hepatic glucolipid metabolism in Chinese perch. Triplicate groups of Chinese perch (29.51 +/- 0.24 g) were fed five isonitrogenous and isolipidic diets containing graded levels of carbohydrate (2.4%, 9.7%, 16.5%, 23.9%, and 30.1%) for 8 weeks. The results based on second-order polynomial regression analysis of specific growth rate (SGR) proved that Chinese perch obtained the best growth performance at the 10.93% dietary carbohydrate level. Compared to 2.4%-carbohydrate group, 9.7%-carbohydrate group exhibited the increase in daily weight gain (DWG) and protein retention ratio (PER) and the decrease in feed conversion efficiency (FCR). Moreover, 9.7%-carbohydrate group showed the increase in the mRNA levels of pfk and cs involved in aerobic oxidation pathway, the content of liver glycogen increased significantly, and no change in glucose level. Above results suggested that a part of carbohydrates may be converted into energy for growth by aerobic oxidation pathway, or converted into glycogen for storage to maintain glucose homeostasis in Chinese perch fed with moderate-carbohydrate diet. Differently, 23.9%-carbohydrate and 30.1%-carbohydrate groups showed the decrease in DWG and PER, and the increase in FCR, compared to 2.4%-carbohydrate group. Additionally, 23.9%-carbohydrate and 30.1%-carbohydrate group presented the increase in the mRNA levels of g6pca and pc involved in gluconeogenesis, which caused the increase in plasma glucose level. However, other plasma indices related to TG-metabolite and its transport (total cholesterol, and low-density lipoprotein) did not show difference, which combined with elevated fatty acid synthesis-related gene acc alpha mRNA level resulted in excessive liver lipid deposition. Above results indicated that unregulated gluconeogenesis and invalid outward transportation of liver TG-rich metabolites may account for the glucose intolerance of Chinese perch fed with carbohydrate-rich diet. Furthermore, compared to the results from the 4th week, the expression of gk, pfk, pc, cs, and acc alpha genes significantly increased in the 30.1%-carbohydrate group at the 8th week. Both liver and muscle exhibited a significant elevation in crude fat content, while Daily DWG experienced a noticeable decrease. These results indicated that the glucose metabolism and growth of Chinese perch in the high-carbohydrate group are influenced by the interaction of feeding duration and carbohydrate levels. And within a certain time frame, Chinese perch can tolerate a diet rich in carbohydrates.