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The present study aimed at developing Montanide oil based inactivated vaccine against Aeromonas hydrophilaand assessing immunogenic potential of two Indian major carps (Rohu: Labeo rohitaand Mori: Cirrhinus mrigala), and a Chinese carp (Grass carp: Ctenopharyngodon idella) commercially cultured in Pakistan. Fishes were randomly distributed in three vaccinated groups with three vaccine concentrations at 108, 109and 1010colony forming unit (CFU)/mL and an unvaccinated control group. Fixed dose of 0.1 mL was intraperitoneally injected to each fish on 1st day and a booster dose at 15 days post-vaccination (DPV). Blood samples were collected at 14, 28, 35, 48 and 60 DPV to determine antibody titers in blood serum using complement fixation test (CFT). Growth parameters were also measured on fortnightly basis. The immune response showed highest antibody Geometric Mean Titers (GMT) on 35 DPV in all vaccinated groups which remained significantly higher than control group till 60 DPV. Fishes were challenged at 60 DPV with infectious A. hydrophilawith 108CFU/mL through immersion bath. The relative percentage survival (RPS) was 89% for fishes vaccinated with 109and 1010CFU/mL potencies while 78% for 108CFU/mL potency. Vaccination did not cause adverse effect on growth performance of fishes. Minor degenerations, with non-significant histopathological changes were observed in few vaccinated fishes as compared to control group in which majority of the fishes presented deteriorative changes in tissues histology.