Positive effect of dietary emodin on growth, antioxidant capacity, inflammatory response, intestinal microbiota and resistance of Micropterus salmoides against MSRV infection

This study aims to investigate the effect of emodin on growth and intestinal microbiota of largemouth bass (Micropterus salmoides) larvae. Five diets, including Con, E25, E50, E100 and E200 diet in which 0, 25, 50, 100 and 200 mg·Kg−1 emodin was supplemented. After a 30-day feeding trail, the results showed the specific growth rate (SGR) of larvae in E50, E100 and E200 group was significantly higher than that of control (p < 0.05). Furthermore, dietary emodin inclusion did not affect the SOD, CAT and GPx activity, while significantly decreased the MDA level (p < 0.05). Moreover, dietary emodin (50 mg·Kg−1) notably enhanced the expression of immune related genes including nrf2, il-1β, tgf-β, ifn-γ, ifn-i and irf3. Additionally, a higher relative abundance of Idiomarina and Halomonas, as well as a lower content of Mycoplasma was observed in E50 group, whereas Enterobacter content remarkably decreased in E200 group at genus level (p < 0.05). Finally, the M. salmoides larvae in E50 group exhibited a relative higher survival rate (p < 0.05), while larvae in E200 group showed a slightly higher mortality than that of control. Collectively, these results demonstrated that proper dosage of supplementing emodin (50 mg·Kg−1) in diet could lead to a promotion of growth performance, immunity, and a protective effect on M. salmoides larvae against MSRV infection. •Dietary emodin (0, 25, 50, 100 and 200 mg·Kg−1) promoted the specific growth rate of M. salmoides larvae.•Dietary emodin (50 mg·Kg−1) notably enhanced the expression of immune related genes including il-1β, tgf-β, ifn-γ, ifn-i and irf3 in M. salmoides larvae.•Dietary emodin (50 mg·Kg−1) remarkably reduced the Mycoplasma content, while multiplied the Halomonas and Idiomarina abundance in intestine of M. salmoides larvae.•Dietary emodin (50 mg·Kg−1) dramatically increased the survival rate of M. salmoides larvae challenged with MSRV.