the effect of different daily feeding frequencies of one time (1X), 2 times (2 X) and 4 times (4 X) on total leucocytes, differential leucocytic counts, phagocytic assay, total proteins, albumin, globulin, AI/GI ratio and antibody titers before and after immunization by intraperitoneally injection (IP) of formalin killed Yersinia ruckri vaccine were Studied as well as histopathological changes. The results proved that (2 X) feeding frequency Causes a marked immunopotentiating effects more than (1X) or (4X) feeding frequencies as well as control groups (1% feeding rates) after IP vaccinations. The immunopotentiating effects of feeding frequencies covered both, the humoral and the cell-mediated immunity response and a marked rise in the antibody titers at day 28 after vaccination which reached to (8.0 + 0.0) in (2X) feeding frequencies after IP. vaccination  compared to the vaccinated control group (4.5 + 0.5: apt. of Aquatic Animal Med., Agric. Res. Cen., Anim. Heal. Res. Inst., Alex. Lab.9.0 t 0.0 and 7.0 + 0.5) in (1X) time feeding frequency, (2X) and (4X) times respectively. Also, lymphocytes, phagocytic assay, total protein and globulin obtained from fish, fed with 2 % feeding rates as well as control ones specially at 2X and 4X frequencies were significantly increased than fish fed with 1% feeding rate in all its treatments. The relative survival percentages after IP. vaccination was 60 %, 50 % in 2 % feeding rates and control groups respectively during 2 X feeding frequencies, compared to the control group where it was 23 %, 30 % and 30 % in 1 X, 2 X and 4 X respectively.