The study had been carried out to evaluate how the fish immune system could be respond to different antigens and what was the most effective antigen that could be used for fish vaccination. In addition, it was to look at the differences between the fish primary and secondary immune responses after antigenic challenge. The fish was intraperitonealy (i.p) injected with bovine serum albumen (BSA) (2.5 mg/mI) as soluble biological antigen, sheep red blood cells (20%) (SRBC(s)) as non-soluble biological antigen and charcoal (2.5%) as non-biological non-soluble antigen, at different time intervals. The primary immune response was assessed at 2, 5, 11, and 14 days postinjection,while the secondary immune response was studied by giving a further injection 19 days after the primary immunization, and the response
was measured at 20, 23, 26, and 29 days. The haemagglutinating antibody productions showed a continuous
increase with a maximum value after 14 days in case of BSA antigen. Although with charcoal and SRBC(s) , the highest values recorded at the 20th day, where they were decreased up to the end of the experiment. The plaque forming cells (PFC) count was increased up to 11 days, followed by sharp decrease until the 14 days, then re-increased again up to 23 days before it was dropped at the end 6f the experimental time. The rosette forming cells (RFC) count nearly showed the same behaviour with the three antigens, where it was increased up to 8 days followed by decrease at 11 and 14 days, then sharply increased after the secondary injection. The total WBCs was increased, while the differential leucocyte
count gave fluctuated results. Although, the percentage of the phagocytic activity was decreased through the primary response, it was increased during the secondary injection with SRBC(s) and decreased with chareoal.