Dietary bile acids reduce liver lipid deposition via activating farnesoid X receptor, and improve gut health by regulating gut microbiota in Chinese perch (Siniperca chuatsi).

The aim of this study is to explore the effects of dietary bile acids (BAs) supplementation on lipid metabolism and gut health of Chinese perch (Siniperca chuatsi), and its possible mechanisms. Two isonitrogenous and isolipidic diets were formulated to supplement different levels of BAs (0 and 900 mg BAs kg-1 diet, respectively). All fish (Initial mean body weight: 171.29 ± 0.77g) were randomly divided into 2 groups (triplicate, 54 fish/group) and were fed with different experimental diets for 56 days, respectively. Dietary exogenous BAs supplementation at the concentration of 900 mg kg-1 significantly increased weight gain and survival rate, and decreased feed conversion ratio. BAs could inhibit lipid synthesis and promote lipid oxidation to reduce lipid deposition by activating farnesoid X receptor (FXR). Dietary BAs supplementation increased the abundance of Lactobacilli in Firmicutes, and the increase of Lactobacillus caused the increase of lactic acid level and the decrease of pH, which might be the reason for the gut villus length and gut wall high in this study. Dietary BAs supplementation increased the levels of catalase and superoxide dismutase and decreased the level of malondialdehyde in the gut and plasma, which might be contributed to the regulating the antioxidant stress phenotype of gut microbiota by the increased abundance of Firmicutes. Then it caused the increase of the globulin level in the plasma, meaning the enhancement of immune state. The increased immunity might also be thought to be responsible for increased survival rate. These results suggest dietary BAs reduce liver lipid deposition via activating FXR, and improve gut health by regulating gut microbiota in Chinese perch.

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.