Abstract:This experiment was conducted to study the effects of dietary bile acids levels on growth, muscle composition and digestive enzyme activities of juvenile Ctenopharyngodon idellus. Five hundred and forty healthy fish, mean body weight of (13.11±0.58) g, were randomly selected and divided into six groups, with three replicates in each group (30 fish/replicate). Each group was fed a diet containing bile acids level of either 0 (control group), 75 mg/kg, 150 mg/kg, 225 mg/kg, 300 mg/kg and 375 mg/kg for a period of 60 days. The results showed that the increase of dietary bile acids levels resulted in an initial elevation of weight gain rate (WGR), specific growth rate (SGR) and followed by a decrease in WGR and SGR when bile acids was 375 mg/kg in the diet. Furthermore, inclusion of 300 mg/kg dietary bile acids produced the highest WGR and SGR (281.18% and 2.23%/d respectively). By contrast, coupled with the increase of dietary bile acids, the feed conversion ratio (FCR) decreased initially and then increased. The FCR reached the lowest (1.26) level when the dietary bile acids level was 225 mg/kg. Based on square regression analysis, to optimize each growth parameter: WGR, SGR and FCR during C. idellus juvenile growth, the most appropriate inclusion levels of dietary bile acids were 222.15 mg/kg, 265.00 mg/kg and 242.86 mg/kg respectively. The crude lipid of muscle during the experiment decreased initially and then leveled out, while the crude protein of muscle increased with the increase of dietary bile acids levels (0–300 mg/kg) and then decreased. Similarly, digestive enzyme activities of segments intestinal and hepatopancreas had a tendency of increasing with the elevated bile acids inclusion and then leveled out at the end. Results indicated that certain range of dietary bile acids levels could promote growth, fat metabolism, reduce fat deposition in muscle and improve meat quality. In conclusion, the bile acids supplementary level of 222.15–265.00 mg/kg is recommended for growing juvenile C. idellus based on the consideration of digestive enzyme activities, meat quality and growth performance.
