Efficacy of orally-delivered virulent Aeromonas hydrophila bacterin vaccines in channel catfish (Ictalurus punctatus)

Authors: Wise, Allison; Beck, Benjamin; Richardson, Bradley; Bader, Troy; PEATMAN, ERIC - Harvest Select Farms; LILES, MARK - Auburn University; BARGER, PRISCILLA - Auburn University; Shoemaker, Craig

Submitted to: Aquaculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/16/2025
Publication Date: 1/1/2026
Citation: Wise, A.L., Beck, B.H., Richardson, B.M., Bader, T.J., Peatman, E., Liles, M.R., Barger, P.C., Shoemaker, C.A. 2026. Efficacy of orally-delivered virulent Aeromonas hydrophila bacterin vaccines in channel catfish (Ictalurus punctatus). Aquaculture. 611:743066. https://doi.org/10.1016/j.aquaculture.2025.743066.
DOI: https://doi.org/10.1016/j.aquaculture.2025.743066

Interpretive Summary: Virulent Aeromonas hydrophila (vAh) is among the top three bacterial pathogens of farm-raised catfish in the United States. This bacterial pathogen infects channel and hybrid catfish inducing skin necrosis, internal and external hemorrhaging, and exophthalmia. Mortality typically occurs rapidly making treatment difficult. Vaccination is a promising solution as it prevents the disease all together. Developing a vaccine that can be orally administered to catfish during feeding provides ease of delivery and less stress put onto the catfish. This study evaluated whether a bacterin vaccine and the addition of an adjuvant would provide protection. We also tested whether this vaccine could cross protect against multiple strains of vAh. Once fish were vaccinated, we exposed fish to vAh 21 days later. Protection was seen in all vaccinated treatments except one (S14-452 with adjuvant). Fish were boosted at 9 weeks and at 12 weeks were exposed to vAh. All fish exposed to any version of the vaccine (with and without adjuvant) were protected compared to placebo vaccinated fish at 12 weeks post vaccination. Results from this study allows for the development of more efficacious vaccine components and delivery on catfish farms, ultimately, preventing mass mortality due to vAh.

Technical Abstract: Virulent Aeromonas hydrophila (vAh) is among the top three bacterial pathogens of farm-raised catfish in the United States. This bacterial pathogen poses a significant economic burden as farmers can lose over 50% of a harvest yield in less than a week when infected. The rapid onset and intensity of mortality due to vAh increases the urgency for a more effective preventative measure. Vaccination represents a potential strategy for prevention of vAh. Killed, recombinant and live attenuated vaccines for vAh delivered via parenteral injection or immersion have been previously tested. However, efficacy and feasibility remain uncertain, prompting ongoing research to develop a more practical and effective vaccine. Oral bacterin vaccination with the inclusion of an adjuvant is a promising solution providing ease of administration for farmers, while decreasing stress put onto the catfish. If successful, oral vaccination enables vaccine application and/or booster at various stages in the production cycle. The aim of this study was to test the efficacy of simple killed vAh formulations delivered by feed either with or without use of an oral adjuvant. Juvenile channel catfish were orally vaccinated and challenged at 21 days post vaccination to evaluate the initial efficacy of the formulated vaccines. Results of survival and hazard analysis at 21 days demonstrated oral vaccination induced protection as compared to the placebo controls except for one preparation. The remaining fish were fed and subsequently booster vaccinated at 9 weeks. At 12 weeks, fish were challenged with both isolates used to formulate the vaccines to examine cross protection. All vaccine formulations yielded improved survival following challenge with either isolate. The hazard ratio revealed that all treatments boosted at 9 weeks with adjuvanted or non-adjuvanted vaccines provided significantly (< 0.01) higher odds of survival compared to the placebo. Serum antibody levels at each time point post vaccination (21 days, 9 weeks and 12 weeks) were unremarkable and like controls (placebo or adjuvant only). Interestingly, we examined survivor antibody responses at 5 d post challenge and antibody levels were significantly elevated in vaccinated survivors. Results suggest the oral vaccination primes the immune system for a rapid response once the virulent pathogen is encountered. Collectively, our findings suggest oral vaccination with a booster dose is a feasible strategy for vaccinating catfish against vAh in the farm setting.