الفهرس 
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Abstract
The present study was planned to: 1) Isolate a pathogenic
strain of A. hydrophila from naturally diseased 0. niloticus and then
evaluate the pathogenicity of the isolated strain through
experimental infection to apparently healthy 0. niloticus. 2) Isolate
and select antagonistic Bacillus species from the gastrointestinal
tract of apparently healthy 0. niloticus based on in-vitro
antagonistic test against A. hydrophila. And then test the safety of
the isolated antagonistic Bacillus species to apparently healthy 0.
niloticus. 3) Evaluate the effect of the dietary application of
antagonistic Bacillus species (1.0 X 107 cfu/g diet) on the immune
response and resistance of 0. niloticus to A. hydrophila infection
after two feeding periods (15 and 30 days). Also the viability of the
Bacillus species in the prepared feed was examined weekly after
storage at refrigerator and at room temperature for up to 6 weeks.
The results can be summarized as follows:
A pathogenic strain of A. hydrophila was isolated from naturally
diseased 0. niloticus showed signs of haemorrhagic septicemia.
The pathogenicity of the isolated strain revealed that intra-
peritoneal inoculation of A. hydrophila (0.5 X 108 cfu/fish) into
apparently healthy 0. niloticus induced 90% mortality among
the inoculated fish. The observed signs and P IM findings on the
experimentally infected fish were similar to that recorded on
naturally diseased fish, including darkening skin, signs of
hemorrhagic septicemia, hyperemia and hemorrhage at different
parts of the body, scales losses, skin erosions, fin rot and
abdominal distension (ascites