Front matter

Fighting infections from the bacteria Streptococcus agalactiae and Aeromonas veronii in Nile tilapia (Oreochromis niloticus) is a hot-topic research for aquaculture. Both bacteria are cosmopolite and are causing high mortality in infected ponds. Moreover, a diseased fish, if consumed raw can easily become a vector for the transmission to animals and/or humans. Prophylactic measures such as fish vaccination are a specific and very effective way of prevention from diseases. In the present study, we aim to demonstrate that immunization is possible in Tilapia. By using inactivated vaccines prepared from formalin-killed pathogens, we were able to produce two monovalent vaccines from Streptococcus agalactiae and from Aeromonas veronii, and a bivalent vaccine from the combination of the two pathogens with a ratio of 1:1. six-hundred and sixty juveniles were acclimated and split into 4 groups in separate aquaria for the first vaccination: 1 control (Ct) and 3 treatments (Sa, Av, Sa+Av) at (day 0). A second booster will be administrated 3 weeks later (day 21) for only half of the fish. From the first day of vaccination, 8 individuals per group** were selected for sampling weekly. Immune response, both systemic and mucosal was characterized for humoral immunity using concentrations in Immunoglobulins M obtained by ELISA and agglutination antibody titer test. In addition, 3 individuals were sacrified each week to provide tissues of head kidneys and liver for IgM gene expression analysis via RT-PCR before, during and after immunization. Prior to the second vaccination, on week 3 (21 days), half of the fish of each group was moved into 12 laboratory aquaria for a future first bacterial challenge at 4 weeks (day 28). The other half of the fish, which received the second vaccination was moved in 12 laboratory aquaria at 12 weeks post vaccination and challenged a week later. Briefly, the challenge is an intra peritoneal injection of a single lethal dose of Streptococcus agalactiae or Aeromonas veronii, respective of the vaccination of the fish. Variability of the survival rates in each challenge group is a direct consequence of vaccination.

Access the project timeline: https://thesistimelinequentin.netlify.app/