الفهرس 
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Abstract
This study describes the bacterial causes of mass mortalities among Giltheadseabream (Sparus aurata) and European seabass (Dicentrarchus labrax) fries, fingerlings, juveniles and adult fish with a total of 320 fish. These bacterial causes include Vibrio alginolyticus, Vibrio parahemolyticus and Photobacterium damselae
subsp. damselae. Diseased fish were characterized by hemorrhages around mouth and pectoral fins, superficial erosions, abdominal distension, skeletal deformities, congestion of kidney and spleen with paleness of liver and gills. Morphological and
biochemical tests were performed to describe the phenotypic properties of purecolonies, while biochemical properties were performed by using conventional tests
and API®20NE system. Further confirmation of Vibrio alginolyticus was performed by using PCR techniques and collagenase gene based primers to produce specific clear 737 bands. Total prevalence of Vibrio alginolyticus, Vibrio parahemolyticus and Photobacterium damselae subsp. damselae among naturally infected Gilthead
seabream and European seabass was 82.19%, 87.28% 10.27%, 6.79% and 7.54%,
5.93% respectively. Physicochemical examination of water revealed that there was direct relationship between unfavorable values of water quality measures and diseased fish. Antibiogram sensitivity test revealed that all the isolated pathogens were sensitive to ciprofloxacin, chloramphenicol, enrofloxacin, oxytetracycline,
nalidixic acid, oxolinic acid and vibriostat (O/129) but resistance was observed to ampicillin, amoxicillin, lincomycin and rifampin.