The potent potential of Gentiana Macrophylla pall aqueous extract in protecting largemouth bass against Micropterus Salmoides Rhabdovirus: A promising application of herbal crude extract in the fight against MSRV

Due to variables such as insufficient host immune system, small size, and high operational costs, there are no commercially available vaccines and drugs against infection by Micropterus salmoides rhabdovirus (MSRV), which leads to serious financial losses in the aquaculture of largemouth bass (Micropterus salmoides). Since herbal extracts are abundant in a range of bioactive compounds and the extraction method is simple and inexpensive, they are more commercially available. In the present study, Gentiana macrophylla Pall (GMP) aqueous extracts rich in a variety of antiviral compounds were found to inhibit MSRV replication in vitro with a half-maximal inhibitory concentration (IC50) of 9.37 mg/L against MSRV, while achieving 99.85% inhibition at 50 mg/L. In addition, GMP was able to reduce MSRV-induced cytopathogenic effect (CPE) and nuclear damage, while decreasing MSRV-induced mitochondrial depolarization, as evidenced by an approximately 0.50-fold reduction in the proportion of JC-1 monomers. Administration of GMP-supplemented commercial diets to MSRV-infected fish significantly increased the expression of host antiviral-related genes while reducing viral load in the spleen and intestine (0.34- and 0.63-fold reduction on 9 day post-infection, respectively), increasing survival rates by up to 18%. In summary, GMP has been shown to have anti-MSRV activity and has the potential for commercial application as an additive against viral diseases in aquaculture based on its low cost and environmental friendliness.