Effects of dietary bile acids on growth performance, serum biochemistry, liver and intestinal health of rice field eel (Monopterus Albus)

In recent years, searching for suitable feed additives to promote the growth, metabolism, and antioxidant capacity of aquatic animals has become an inevitable task for the aquaculture industry. The purpose of this trial was to study the effects of dietary bile acid (BAs) on growth performance, body composition, serum biochemical indexes, as well as liver and intestinal health of Monopterus albus. 1 200 eels (23.00±0.05) g were randomly divided into 5 groups with 4 replicates in each group. The fish in the five groups were fed isonitrogenous diets supplemented with 0, 125, 250, 375 and 500 mg/kg BA, and named as CON, BA125, BA250, BA375 and BA500 groups, respectively. The results of the 56-day feeding experiment showed that as the amount of BA increased, the final average weight, weight gain rate, and specific growth rate first increased and then decreased, with significantly higher figures in the BA250 group compared to the CON and BA500 groups. The feed conversion ratio showed a trend of first decreasing and then increasing. The crude protein content in whole body increased firstly and then decreased, while the trend for crude lipid content in liver was the opposite. The activity of serum glutamic pyruvic transaminase in the CON group was significantly higher than in the other groups, while the activity of glutamic oxaloacetic transaminase showed a trend of first decreasing and then increasing. The content of D-lactic acid decreased gradually, while diamine oxidase activity decreased at first and then increased. Compared with the CON group, the liver structure of the BA125 and BA250 groups was more intact. Excessive BA (BA375, BA500 groups) caused vacuolation and rupture of hepatocytes. The number of lipid droplets in liver decreased at first and then increased. The mRNA expression levels of acc and dgat2 in the liver showed a decreasing trend, while the mRNA expression level of cpt1 first increased and then decreased, and the mRNA expression level of pparα was highest in the BA375 group. The intestinal villus width and muscle layer thickness increased at first and then decreased, but the villus height and villus width in BA500 group were significantly lower than those in CON group. The total superoxide dismutase activity in the liver showed a gradual upward trend, with the highest glutathione peroxidase activity and catalase activity in the BA250 group, and the lowest malondialdehyde content in the BA250 group. The activities of total superoxide dismutase and glutathione peroxidase in the intestine both showed a trend of increasing first and decreasing afterwards, while the trend of malondialdehyde was the opposite, with the BA250 group significantly lower than the CON and BA375 groups. The mRNA expression levels of the intestinal tight junction protein genes zo1, zo2, and occludin all showed a significant trend of increasing first and then decreasing. The study showed that the addition of appropriate amounts of BA to the feed can improve the growth performance of Monopterus albus, enhance the antioxidant capacity of the liver and intestine, reduce lipid deposition in the liver by increasing lipid catabolism and inhibiting lipid synthesis, and alleviate liver damage and improve liver and intestinal function. The suitable dietary addition amount of BA in M.albus is 250.0-283.3 mg/kg.