Dietary addition of fraxetin improved intestinal structure and growth performance in juvenile grass carp (Ctenopharyngodon idella): As a potential novel phytogenic feed additive.

The well-being and development of fish are affected to varying degrees under the intensive aquaculture model, and the use of Chinese herbs for aquaculture disease control and feed additives has received increasing attention. This study examined fraxetin supplementation in juvenile grass carp to investigate its effects on growth and intestinal structure. There were 1080 grass carp (11.58±0.01 g) assigned to 6 treatments, fed with fraxetin (0, 3.9, 7.9, 15.8, 31.5, and 63.1 mg/kg) for 60 d in each treatment. In our study, appropriate fraxetin significantly increased final body weight (FBW), percent weight gain (PWG), and specific growth rate (SGR) compared to the unadded group (P<.05), but did not affect feed efficiency (FE) (P>.05). The administration of 7.9 mg/kg of fraxetin significantly improved fish intestinal development and body composition. Appropriate dietary fraxetin significantly enhanced intestinal digestive enzymes and brush border enzyme activity (P<.05), decreased serum diamine oxidase (DAO) levels (P<.05), and decreased intestinal cell apoptosis (P<.05). Appropriate levels of fraxetin inhibited the RhoA/ROCK signaling pathway while upregulating both mRNA and protein expression of tight junction (TJ) and adherens junction (AJ) (P<.05). These changes significantly improved apical junction complex (AJC) integrity. In conclusion, dietary supplementation with appropriate levels of fraxetin added to the diets had a facilitating effect on digestion and absorption, improved intestinal structure, and promoted fish growth performance in juvenile grass carp. In addition, the optimal dietary fraxetin levels were evaluated to be 6.06 and 7.79 mg/kg based on linear regression analysis of PWG and DAO, respectively.