الفهرس 
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Abstract
Pseudomonas flurescens is widely distributed in aquaculture and is considered as one of the primary cause of bacterial hemorrhagic septicemia .
The identification of the previously mentioned P. Flourescence were based on the criteria of Herbe (2002) .
The bacteria isolated from naturally infected fish comprised Gram negative cocci, motile, catalase and oxidase negative, grow on trypticase soy agar colonies were pin point, whitish in color , and production of acid from glucose and maltose .
The results of invitro susceptibility of P. Flourescence (sensitivity test) was highly sensitive to Lincospectin, Neomycen, Oxanilic acid, Enerofloxacin , and Ampicilin .
The Clinical signs appeared in the experimentally infected fish were in the form of opacity of the eye, erosions of the tail fin , scale loss, haemorrhage of the dorsal surface, congestion of pectoral fin and some fish suffered from slight exophthalmia and darkness coloration.
In experementally infection with P. Flourescence the clinical signs were manifested as, loss of scales from some areas of the body with excessive mucus allover the body surface and petechial haemorrhages over the body .
In the present study the LD50 for P. flourecence in O. niloticus was 102 in P. Flourescence .
Our results cleared that the Effect of Pseudomonas fluorescens infection on differential leucocytic counts :
The lymphocyte showed a tendancy to decreasing from the 1st week .
In our study there was increase in both lymphocytes and monocytes especially with increase of total leucocytic count at the first weeks of infection and this mainly due to the direct effect of stress on the immune response and activation of first line of defense to resist the infection through cellular immune response .
Concerning the effect of Pseudomonas fluorescens on Phagocytic activity and Phagocytic index :
The Phagocytic activity increased progressively from the 1st week to the 4th week .
The GPT level decreased progressively from the 1st week to the 3rd week of the experiment and increased at the 4the week of the experiment , and its level in infected group higher than that of the control group.
The total protein level increased progressively from the first week to the last week and the level of total protein in infected group lower than that of control group.
The total cholesterol level decreased progressively from the 1st week to the 4th week of the experiment and reached to its highest level at the 1st week and its minimum level observed in the 4th week of the experiment.
While histopathological results indicated that hepatocytes started with dilated blood vessels and ended by hydropic degeneration .
The successful reproduction of the disease experimentally leaves no doubt about the pathogenicity of P. Flourescence to cultured fish. The fact that infection could occur following the presence in water contaminated with P. Flourescence confirms the invasive character of the organism.