Abstract: In order to investigate the characteristics of LMBV-ZJDSS-F110, an attenuated transmissible strain of Largemouth bass virus (LMBV), this study examined various factors, including replication efficiency, virulence, in vivo viral load changes, comparative genomes, immune protection rate, expression of immune-related genes after immunization , and virulence regression of the virus. The results showed that, when cultured in FHM, the viral titer of F110 generation reached 10^9.1 TCID₅₀/mL, and no mortality was observed in largemouth bass when injected at a dose of 10^8.0 TCID₅₀/mL×0.1 mL. Tissue viral load tests on different generations of strains showed that the viral loads in spleen and gills of transmission strains F5, F45, and F110 were higher in the 7d than that in the 3d, whereas the viral loads of F90 did not change significantly at the two time points, which indicated that the characteristics of the transmission strain F90had changed compared with those of F45 and F110. Comparative genomic analyses of the F5 and F110strains showed that LMBV-ZJDSS-F110 exhibited 10 mutations, of which 7 could cause changes in the coding region. Immunization trials using both injection and immersion showed that the 10^8.0 TCID₅₀/mL concentration group obtained 70% immune protection rate against the strong F5strain. Gene expression of immune factors (TNF-α, CD8b, IgM, IgT, IFN-γ) in the head and kidney reached a peak on the 14d after immunization and was significantly higher in the injected group than that of the immersion group, with the expression of IFN-γ was significantly higher. Specifically, the expression of IFN-γ was nearly 50 times that of the control group. The results of in vivo virulence test showed that F110 did not cause any mortality in 5 generations of blind in vivo transmission. The above studies indicate that LMBV-ZJDSS-F110 is a safe and effective weakly virulent vaccine strain, which provides a pathway for the immunization of largemouth bass virus.