الفهرس 
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Abstract
The present work was carried out on 320 Tilapia species which were collected alive or freshly dead at different periods throughout the year, total prevalence among naturally infected
Tilapia species with Ph. damselae, Ps. putida, F. columnare and Strept. fecalis was (18%),(10.3%), (5%) and (5%) respectively. The main clinical pictures were darkness of the skin,
hemorrhages all over the body surface, anal prolapse, tail rot, deep ulcerations. In addition to
generalized congestions of the internal organs. Bacteriological investigations of isolates were
done by morphological, colonial, biochemical characters and confirmed by the results of API®
20 E, NE and Strep., further confirmation of Ph. damselae using PCR, producing clear and
expected 267 bp bands corresponding to the 267 bp internal fragments of the 16S rRNA gene of
Ph. damselae, beside all the biochemical tests especially, urease +ve, concluded that it’s
Photobacterium damselae subsp. damselae. Physico- chemical examination of water samples
revealed, alkaline pH, Total dissolved solids were high, toxic un-ionized ammonia and Nitrite
concentrations exceeded the admissible limits in all water samples. Heavy metals detected in
water samples, in which Cu, Zn and Pb exceeded the permissible limits in Deir-El Birka drain,
Fe was severely high in almost most of water samples. Bacteriological examination of the water
samples showed presence of coliform bacteria especially in Deir-El Birka drain. Heavy metals
determined in Tilapia sp. musculature showed that, Pb and Fe exceeded the permissible limits.
Experimental infection carried out by injection of O. niloticus and Clarias gariepinus with
different pathogens, where mortality rates detected within 21 days of the experiment and Reisolation
of the injected pathogens took place. Antibiotic sensitivity test showed that all the
pathogens were sensitive to Danofloxacin and resistant to Amoxicillin, Tetracycline and
Clamoxyl. In addition to the sensitivity of Ph. damselae subsp. damselae to Vibriostat (O/129).