Effects of dietary D-mannose supplementation on growth performance, intestinal digestive capacity, gut microbiota, and ammonia tolerance of largemouth bass Micropterus salmoides

To investigate the effects of D-mannose on the growth performance, intestinal digestion capacity, intestinal microbiota composition, and ammonia tolerance of largemouth bass, experiments were conducted using largemouth bass fry with an average body weight of 7.41±0.05 g. Three experimental groups were designed, with 3 replicates per group and 30 fish per replicate. The fish were fed with feed containing different concentrations of D-mannose (0.00%, 1.00%, and 2.00% - Control, 1% mannose, 2% mannose) and were given full satiation twice a day for 56 days. The results indicated that the addition of 2% D-mannose in the feed enhanced the growth performance of the largemouth bass while reducing the feed conversion ratio. The addition of D-mannose in the feed increased the activity of digestive enzymes in the intestines (lipase, α-amylase, pepsin, alkaline phosphatase, Na+/K+ATPase, gamma-glutamyl transpeptidase, and creatine kinase). It also led to an increase in intestinal villi height and intestinal wall thickness; Adding D-mannose reduced the abundance of Staphylococcus and Achromobacter in the gut microbiota, while increasing the abundance of Aurantimicrobium. After being subjected to ammonia stress for 96 hours, the addition of D-mannose in the feed resulted in a decrease in mortality rate and neuronal nitric oxide synthase activity, while simultaneously enhancing the activity of liver argininosuccinate synthetase, argininosuccinate lyase, arginase, ornithine transcarboxylase, and inducible nitric oxide synthase. Adding D-mannose to the feed promotes the growth of largemouth bass, enhances their digestive capacity, and has a positive impact on their intestinal microbiota composition. Furthermore, it has been demonstrated that it can enhance the tolerance of largemouth bass to ammonia.