Effects of dietary sodium deoxycholate on the growth, glucose metabolism and intestinal microbiota of largemouth bass (Micropterus salmoides)

Bile acids play an important role in glucose metabolism, lipid metabolism, and they can also help to maintain the liver health and intestinal homeostasis in animals. In recent years, bile acids have been widely used as new additives in aquatic feeds. However, so far, most of the bile acid products used in aquaculture are mixed bile acids. There are many different kinds of bile acids, and different bile acids have different effects on the growth and metabolism of fish. Therefore, it is necessary to evaluate the effects of different bile acids on fish growth and metabolism to select the appropriate type of bile acids for precise nutritional regulation. This experiment was conducted to evaluate the effect of sodium deoxycholate as a feed additive on Micropterus salmoides. Two experimental diets were formulated to contain different sodium deoxycholate levels of 0, and 300 mg/kg referred to as CON and SD, respectively. The effects of sodium deoxycholate on the growth condition, metabolic characteristics and intestinal microbiota were analyzed. M. salmoides (10.80 ± 0.12) g were cultured for 8 weeks. The results showed that sodium deoxycholate significantly increased the final body weight (37.24 ± 0.64) g in the control group and (46.87 ± 1.44) g in the sodium deoxycholate group. The body length was (12.42 ± 0.12) cm in the control group and (13.07 ± 0.14) cm in sodium deoxycholate group. The condition factor (CF) was (1.95 ± 0.06) g/cm³ in the control group and (2.09 ± 0.03) g/cm³ in the sodium deoxycholate group, but there was no significant difference in viscera index (VSI) or hepatosomatic index (HSI). Sodium deoxycholate had no effect on the total lipid and crude protein of whole fish. Sodium deoxycholate significant increased the expression level of gluconeogenesis-related and glycolysis-related genes in liver and muscle, and the sodium deoxycholate promoted the glycogen accumulation in muscle (0.31 ± 0.03) mg/g in control group and (0.46 ± 0.03) mg/g in sodium deoxycholate group by increasing the activity of glycogen synthase, but there was no significant difference in the liver glycogen content between these two groups. In addition, sodium deoxycholate significantly increased bile acids content in gallbladder (199.4 ± 12.72) μmol/L in control group, (341.1 ± 8.52) μmol/L in sodium deoxycholate group. Our results indicated that sodium deoxycholate can promote the bile acid synthesis mainly by down-regulating the expression level of fxr gene and up-regulating the expression level of cyp7a1 gene in the liver. The abundance of Firmicutes and Bacteroidetes decreased while Actinobacteria increased in M. salmodides fed with sodium deoxycholate at the phylum level. All these results suggested that sodium deoxycholate can be used as a feed additive for M. salmodides to promote the growth condition, and increase muscle glycogen accumulation and bile acid synthesis.