Effects of combined application of nucleotides and β-glucan on intestinal health and flesh quality in grass carp (Ctenopharyngodon idella)

Nucleotides and β-glucan have demonstrated positive effects on the growth and health of aquaculture species. However, little research has been done on the combined effects of using both supplements on the intestinal health and flesh quality of fish. In the present study, we evaluated the impact of nucleotides (0.01 %) or/and β-glucan (0.10 %) on parameters related to intestinal health and flesh quality in grass carp (69.97 ± 0.05 g) over a 60-day feeding period. The results showed that both nucleotides and β-glucan significantly increased catalase activity, enhanced mRNA expression level of zonula occludens-3, downregulated interleukin-1β, interferon, Toll-like receptor-4, and Toll-like receptor-7 expression in the intestine (P < 0.05). Additionally, they also resulted in enhanced springiness and increased percentage of total unsaturated fatty acids, while reducing Myostatin 1 expression and total saturated fatty acids content in the muscle (P < 0.05). This indicates that these supplements have similar effects in promoting oxidation resistance, suppressing inflammation, and improving intestinal barrier integrity and flesh quality in grass carp. Besides, the combination of nucleotides and β-glucan led to a decrease in Firmicutes abundance and an increase in Actinobacteria compared to the control group. We further observed the synergistic effects of nucleotides and β-glucan in decreasing the expression of inflammation related genes (interleukin-1β, interferon, Toll-like receptor-4, and Toll-like receptor-7) and improving parameters associated with intestinal morphology (villus height, villus width and gut wall thickness) and flesh quality (chewiness, springiness, total tasty free amino acids, total saturated fatty acids and total unsaturated fatty acids). Overall, our results suggest that the combined application of nucleotides and β-glucan is more effective in promoting intestinal health and improving flesh quality in grass carp compared to using either supplement alone.