Aeromonas hydrophila is responsible for heavy mortality to f»h stocks specially under culturing conditions. It is usually associated with the development of fish bacterial haemorrhagic septicemia. Therefore, the need for protection and treatment programmes is increasingly called on to avoid and/or overcome disease outbreaks in fishery populations.
The haematological studies were carried out including the total erythrocytic count, haemoglobin estimation, packed cell volume "PCV11 and the total and differential leucocytic counts. Various derived values can be calculated from these results, such as mean corpuscular volume "MCV", mean cell haemoglobin "MCH" and mean corpuscular haemoglobin concentration "MCHC". The haematologjcal changes in the blood of common carp induced after the i.p. injection with Aeromonas hydrophila pathogen weie 
blood cells, haemoglobin concentration and haematocrit values. These increments were due to the tissue hypoxia resulting from erythropenia caused by Aeromonas hydrophila infection. Treatment of the infected fishes with both laminarin and N. sativa showed a decrease in the RBCs count and haemoglobin concentration to the range of subnormal level A marked decrease in the RBCs count beyond the normal value and a noticeable increase in the haemoglobin concentration were noticed at the 5lh week and the 4th and 5th weeks, respectively in the K sativa treated group. The PCV values were changed in a fluctuated manner parallel to the changes in the quantities of circulating RBCs and/or modified erythrocyte cellular volume.In the protected groups, the haematological changes reflected the same effects of the immunopotentiators recorded in the treated ones. Also, following the challenge with bacteria, there was a decrease in the RBCs count, haemoglobin concentration and PCV values. Furthermore, the blood indices were calculated to interrupt and to give valuable support for the haematological results,The total leucocyte counts was increased after the challenge with bacteria, then a further elevation was recorded during the time of treatment with both of the immunopotentiators. Also, in the protected groups, the leucocyte counts was increased with laminarin and N. sativa injection. While it remained nearly unchanged following the infection with bacteria in the laminarin protected group, it was decreased in the N. sativa protected one.The increased leucocyte counts were accompanied by an increase in the neutrophils and a decrease in the lymphocytes following the infection with bacteria and injection with N, sativa in both protected and treated groups, Meanwhiles, in the groups injected with laminarin, the neutrophil and lymphocyte counts were nearly fluctuated around the control values. In addition, monocytes were increased in all the studied