The virulence of strain GJL1 was confirmed by experimental infection; the median lethal dosage (LD50) of the GJL1 for largemouth bass was 3.6 × 105 CFU/mL, and histopathological analysis revealed that the isolate could cause obvious inflammatory responses in M. salmoides. Additionally, the immune-related gene expression in M. salmoides was evaluated, and the results showed that IgM, HIF-1α, Hep-1, IL-15, TGF-β1, and Cas-3 were significantly upregulated after A. veronii infection. This evidence concerns the gene IL15 and infection.