Effects of dietary carbohydrate to lipid ratios on growth, biochemical indicators, lipid metabolism, and appetite in Chinese perch ( Siniperca chuatsi )

An 8-week feeding trial was conducted to evaluate the effects of dietary carbohydrate to lipid (CHO:L) ratios on growth performance, body composition, serum biochemical indexes, lipid metabolism, and gene expression of central appetite regulating factors in Chinese perch ( Siniperca chuatsi ) (mean initial weight: 12.86 ± 0.10 g). Five isonitrogenous and isoenergetic diets (fish meal, casein as main protein sources) were formulated to contain different graded CHO:L ratio diets ranging from 0.12, 0.86, 1.71, 3.29, and 7.19. Each diet was assigned to triplicate groups of 18 experimental fish. Our results revealed that final body weight (FBW), weight gain rate (WGR), specific growth rate (SGR), and protein efficiency ratio (PER) increased with dietary CHO:L ratio from 0.12 to 1.71 and then decreased with further increases in dietary CHO:L ratio. A two-slope broken-line regression analysis based on WGR showed that the optimal dietary CHO:L level for maximum growth performance of fish was 1.60. Crude lipid and crude protein content in the liver and glycogen concentration in the muscle and liver were significantly influenced by the dietary CHO:L ratios ( P < 0.05). The lowest crude lipid content in the liver was observed in fish fed the diet with a CHO:L ratio of 1.71( P < 0.05). Dietary CHO:L ratios significantly induced the glucose concentration of serum ( P < 0.05). The relative expression levels of genes involved in lipid metabolism, such as srebp1 and fas in the liver, showed a trend of first decreased and then increased with the increase of dietary CHO:L ratio levels. Appropriate CHO:L ratio in the diet can effectively reduce the accumulation of liver fat. We observed in fish fed the 1.71 CHO:L ratio diet showed higher feed intake, up‐regulated mRNA expression of neuropeptide Y ( npy ) and agouti gene-related protein ( agrp ), and down‐regulated mRNA expression of cocaine- and amphetamine-regulated transcript ( cart ) and pro‐opiomelanocorticoid ( pomc ) significantly as compared to control group. Thus, these results provide the theoretical basis for feed formulation to determine the appropriate CHO:L ratio requirement of Chinese perch.