Enhancing nile tilapia (Oreochromis niloticus) broodstock and fry health through vaccination against streptococcus agalactiae and aeromonas veronii | |
| Author | Valarezo, Andrea Nathaly Pardo |
| Call Number | AIT Diss. no.AQ-25-01 |
| Subject(s) | Tilapia--Diseases--Prevention Tilapia--Vaccination |
| Note | A dissertation submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Aquaculture and Aquatic Resources Management |
| Publisher | Asian Institute of Technology |
| Abstract | Disease outbreaks caused by Streptococcus agalactiae and Aeromonas veronii remain major obstacles to the sustainable production of Nile tilapia (Oreochromis niloticus), a key species for global food security and economic development. The growing threat of antimicrobial resistance underscores the need for safe, scalable, and farmer-feasible disease-prevention strategies, positioning vaccination as a key preventive measure of sustainable aquaculture health management. The main objective of this study was to evaluate vaccination strategies targeting broodstock and fry of Nile tilapia to enhance protection against two major bacterial pathogens, S. agalactiae and A. veronii.This dissertation comprises one comprehensive review and two independent experimental studies designed to enhance bacterial disease resistance in tilapia through vaccination at different life stages. The review synthesizes current knowledge on parental immune transfer in fish, emphasizing how broodstock vaccination can promote transgenerational immunity and how early-life vaccination may complement this protection to reduce vulnerability during critical developmental periods. It highlights opportunities to integrate broodstock and fry immunization strategies into practical health programs tilapia production.The first experimental study optimized and evaluated a heat-inactivated bivalent vaccine targeting S. agalactiae and A. veronii in broodstock. Vaccinated broodstock developed significantly elevated antigen-specific IgM titers following primary and booster immunizations. Maternal IgM was detected in fertilized eggs, confirming transgenerational transfer, though levels declined after yolk-sac absorption. Passive immunization tests using sera from vaccinated broodstock yielded relative percent survival (RPS) values of 83.3% against S. agalactiae and 35.7% against A. veronii, demonstrating the protective function of maternally derived antibodies. This study developed a novel heat-killed bivalent vaccine for Nile tilapia and provided new insights into humoral immune response kinetics in broodstock, along with evidence of protective transgenerational immunity transfer. These findings indicate that broodstock vaccination is a promising biosecurity strategy for enhancing broodstock immunity.The second study evaluated an oral bivalent microencapsulated inactivated vaccine for fry, delivered via coated commercial feed to simulate farm-feasible application. While oral vaccination did not induce significant IgM titers, it did trigger measurable upregulation of immune-related genes (IgT, IgM, CD4, CD8, TNF-α, and IL-1β) in spleen and hindgut tissues, particularly on D35. The vaccine conferred partial protection against A. veronii (RPS = 57.9%), though protection against S. agalactiae was limited. The findings suggest that oral vaccination for tilapia fry is highly promising, while optimization of the vaccination program to improve protection warrants further investigation.Although the two studies were performed independently, their results provide complementary insights into immunity at different developmental stages. Maternally transferred IgM provides early passive protection during the initial life stages, while oral vaccination stimulates the fry’s developing immune system as maternal antibodies naturally decline. Together, these findings support the idea that broodstock and fry vaccination may be combined in future work to broaden protection throughout early development. Thus, this dissertation advances understanding of transgenerational immunity and early-life immune stimulation in Nile tilapia and outlines practical, low-cost vaccination strategies that may help reduce antibiotic use, mitigate antimicrobial resistance, and strengthen sustainable aquaculture health management. |
| Year | 2025 |
| Type | Dissertation |
| School | School of Environment, Resources, and Development |
| Department | Department of Food, Agriculture and Natural Resources (Former title: Department of Food Agriculture, and BioResources (DFAB)) |
| Academic Program/FoS | Aquaculture and Aquatic Resources Management (AQ) |
| Chairperson(s) | Ha, Thanh Dong;Salin, Krishna R. (Co-chairperson); |
| Examination Committee(s) | Datta, Avishek;Thi, Phuoc Lai Nguyen; |
| Scholarship Donor(s) | IFS2023 Project;AIT Scholarship; |
| Degree | Thesis (Ph.D.) - Asian Institute of Technology, 2025 |