in order to asses the immunogenicity of Aeromonas hydrophila, the aethiological cause of haemmorhagic septicemia in common carp in Fars province fish farms, three different preparations of antigen including formalin-killed cell (1%) heat killed cell (60°C, 4h) and live cell were studied. Fifty five common carp (Cyprinus carpio, L) in 9 groups with three routes of administration were exposed to the antigens (oral administration 1O9 cell/mi/fish, immersion 1O7 cell/mi/fish and ip injection 10 cell\fish) in day 0 and day 20 of the experiment. Similarly 15 fish in three groups were exposed with phosphate-buffered saline as control. Fish were bled 45 and 60 days after immunization and serum sample from each fish was collected. The fish humoral response was detected by ELISA. Results showed that the formalin-killed cell had the best response and that oral administration of antigens in comparison with other routes had the highest effect. The antibody level of fish was still increasing at day 60.
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