Aeromonas hydrophila is one of the serious bacterial pathogen in fresh water aquaculture industry. Recently, some attention has been given to bacterial outer membrane protein (BOMP) as potentially important vaccine components. Ornamental gold fish Carassius auratus immunized with the bacterial outer membrane protein encoding gene clone, BOMPG-pTZ57R/T that was named as BOMPG and the bacterial outer membrane proteins (BOMP) which were developed from a virulent strain of A. hydrophila and used as a vaccine candidate. In order to study the comparative effects of the vaccines, BOMPG and BOMP were delivered to the experimental fishes (16.4 ± 1 g mean weight) by intra peritoneal injection once in every 15 days interval. At the end of the experiment, the immunized and control fishes were challenged with virulent strain of A. hydrophila and assessed the immunological parameters. C. auratus succumbed to death 100% at five days when no vaccination was given whereas the vaccinated groups survived significantly (F=34.64; P ≤ 0.001) of 70 and 80% respectively in BOMPG and BOMP after 10 days of challenge. Surprisingly the vaccinated groups help to decrease the Aeromonas sp. load in blood and muscle of treated fishes and improve the serum biochemical parameters significantly (P ≤ 0.001) than the control group. The haematological and immunological parameters were also improve significantly (P ≤ 0.001) in the BOMP vaccinated fishes due to the immune enhancement by the vaccines. Among the two different BOMP deliveries, the BOMP highly influenced to improve the immune system against A. hydrophila challenge than BOMPG. It may be the reason the BOMPG vaccine may easily degraded in vivo conditions.