Optimal Isatidis Radix extract enhances growth, immunity, modifies immune-gene action and intestinal health in hybrid snakehead (Channa maculata ♀ × Channa argus ♂) against rhabdovirus.

Isatidis Radix is a traditional Chinese medicinal herb renowned for its broad-spectrum antimicrobial, antiviral, and anti-inflammatory properties. This study assessed the effects of Isatidis Radix extract on growth performance, non-specific immunity and intestinal health and disease resistance in hybrid snakehead (Channa maculata ♀ × Channa argus ♂). Fish were fed diets supplemented with Isatidis Radix extract at concentrations of 0 (C), 0.5 % (IRE0.5), 1.0 % (IRE1.0), 1.5 % (IRE1.5), and 2.0 % (IRE2.0) for 8 weeks. The results showed that with the increase of Isatidis Radix extract levels, the weight gain rate (WGR) and specific growth rate (SGR) significantly increased and reached the maximum at 1.5 %. The serum and liver activities of phosphatase (ACP), alkaline phosphatase (AKP), aspartate aminotransferase (AST), and alanine aminotransferase (ALT) in the Isatidis Radix extract supplemented group were significantly lower than those in the control group, demonstrating a dose-dependent decrease as the concentration increased. Antioxidant enzyme activities, such as superoxide dismutase (SOD) and catalase (CAT) in the IRE1.5 group were significantly elevated, whereas malondialdehyde (MDA) content were decreased. The IRE2.0 group demonstrated significant upregulation of intestinal antioxidant genes, including sod, cat, kelch-like ECH-associated protein 1 (keap1), and glutathione peroxidase (gpx), while the pro-inflammatory factors interleukin-1 beta (il-1β) and tumor necrosis factor-alpha (tnf-α) were significantly down-regulated. The 16S rRNA analysis indicated that the IRE1.0 group exhibited the highest Chao,the abundance of potentially pathogenic Proteobacteria was reduced, while the abundance of beneficial bacteria Acidobacteriota, Staphylococcus, and Glutamicibacter increased. The cumulative survival rate of hybrid snakeheads after rhabdovirus infection increased in a dose-dependent manner following the administration of Isatidis Radix extract in their diet. In conclusion, this study indicated that dietary Isatidis Radix extract (1 %-1.5 %) significantly improved the growth performance, antioxidant capacity and antiviral resistance of juvenile hybrid snakehead.