A highly pathogenic isolate of Aeromonas hydrophila, isolate No1, was identified through evaluation of the Crude extra-cellular product and estimation of LD50. Three types of formalized whole culture Aeromonas hydrophila vaccine (FWC) were prepared, FWC vaccine alone, FWC vaccine mixed with Freund's complete adjuvant (FCA), and FWC vaccine mixed with Freund's incomplete adjuvant (FIA), tested for sterility and administered to female Nile tilapia (Oreochromis niloticus) using two methods of delivery. Micro-agglutination and the double immuno-diffusion tests were performed on serum, mucus and eggs to evaluate maternal immunity. The relative level of protection (RLP) was calculated after challenge infection.
Vaccine safety showed that fish vaccinated with FWC vaccine +FCA expressed severe skin lesions and died. RLP of formalin-inactivated whole culture vaccine alone (S/C or I /M) or incorporated with FIA (I/M) protected 100, 88.8 and 91.1 percent of vaccinated fish, respectively. Subcutaneous administration of the vaccine incorporated with the adjuvants provided partial protection, 66.6%.
Serum and mucus showed increased agglutinins four and six weeks post initial vaccination and up to the 8th week in FWC vaccinated fish and fish subcutaneously vaccinated with FWC+FIA. The agglutinating antibodies from eggs of vaccinated females had an agglutinating titer of 160 compared to 10 in the control.