Master Thesis - Immune response and protection of fry Nile tilapia (*Oreochromis niloticus*) immunized by immersion and oral bivalent vaccines against *Streptococcus agalactiae* and *Aeromonas veronii*

Abstract

Aquaculture has made significant strides in providing a sustainable and efficient protein source. However, bacterial infections such as those caused by Streptococcus agalactiae and Aeromonas veronii remain a persistent challenge, affecting the health and productivity of Nile tilapia (Oreochromis niloticus) fingerlings. This study aimed to assess and compare the efficacy of two bivalent inactivated vaccines administered through different methods: oral vaccine followed by an oral booster (OR+OR) and immersion vaccine followed by an oral booster (IM+OR). Two cohorts of Nile tilapia fingerlings (1.1 +- 0.1 g) were randomly assigned to two tanks (150 fish/tank). In the OR+OR group, fish were immunized with an oral vaccine on days 1-7, followed by a daily oral booster on days 21-28. In contrast, the IM+OR group received an immersion vaccine on day 1, supplemented with a daily oral booster on days 21-28. Key measurements included IgM antibody levels against both Streptococcus agalactiae and Aeromonas veronii, as well as survival rates post-artificial infection. The findings shed light on the vaccine’s capacity to stimulate IgM responses and confer protective immunity against these bacterial pathogens. I found that for those formulations specifically, immersion was more effective in conferring protective efficacy for a few months and that oral vaccines were more appropriate to be given as a booster after primer vaccination. The outcomes from this study offer valuable insights into optimal vaccination strategies for enhancing aquatic animal health in aquaculture, specifically for Nile tilapia.

Quentin Andres

Second Year PhD Candidate in Fisheries Science and Technology (International Program)

Specializing in aquaculture, molecular biology, genomics, and bioinformatics.