An inactivated bivalent vaccine effectively protects Carassius auratus against Aeromonas caviae and Aeromonas veronii.

Aeromonas veronii (A. veronii) and Aeromonas caviae (A. caviae) are important pathogens that affect various fish species. In this study, a whole-cell bivalent vaccine against A. veronii and A. caviae was developed to assess the immune response of Carassius auratus(C. auratus). Initially, the inactivation temperature and formalin concentration were investigated. After confirming safety, three different vaccine concentrations were administered via injection, and a random selection of C. auratus was subjected to tail vein blood collection. The serum levels of SOD, CAT, IgM, AKP, LZM, ACP, complement C3 and complement C4 were determined. Real-time fluorescence quantitative PCR was used to measure gene expression in the liver, spleen, kidney, and intestinal tissues. On the 35th day, a challenge test was conducted to determine the immune protection rate of the vaccine. The results demonstrated that serum IgM antibody levels increased significantly in all vaccine groups after the initial immunization and continued to rise following the second booster immunization. Additionally, there was a notable increase in the levels of SOD, CAT, AKP, LZM, ACP, C3, and C4 in the serum after both immunizations, with peak values observed on Day 21. Real-time quantitative PCR revealed upregulation of IL-10, IL-1β, IFN-γ, and TNF-α expression after both immunizations, with the maximum levels occurring on the 21st day, followed by a decrease on the 28th day. This study investigated the effect of different vaccine concentrations on the immunological protection rate of C. auratus, aiming to provide a fundamental theoretical basis for double-vaccine preparation.