الفهرس 
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Abstract
The present study was planned to investigate the most bacterial pathogens affecting some cultured fishes Sea bass, Gilt-head sea bream and Mugil capito. The study was carried on 47 naturally infected cultured fish and fry of sea bass collected from private farm in Damitta and private marine hatchery. Disease problems occur during the period study on sea bream were investigated focusing on the isolation, characterization, antimicrobial resistance, pathogenicity of the bacterial isolates affecting fish, histopathological alteration and PCR.
The result of these studies was summarized as follows:-
1-The common clinical signs in examined fish were mass mortalities in the farm in Gilthead sea bream. But Mugil capito showed hemorrhages on several parts of the body surface, mouth, base of the fins, abdomen, and opercula and around the anal opening, darkness of skin and fryed fins. Fingerlings of Mugil capito showed sever hemorrhage in skin and fins but in case of Tilapia zilli showed exophthalmia and darkness of skin.
2-The observed postmortem examination of diseased Sea bass and Gilt-head sea bream showed pale anemic liver with hemorrhage on its edge and congested gills and ovaries. In some cases petechial hemorrhage on pale liver with congested spleen and eroded gills In case of Mugil capito showed distended abdomen with ascetic fluid and paleness of liver. Diseased Tilapia zilli show sever enlarged liver with paleness and enlarged abdomen with ascetic fluid.
Suspected colonies on tryptic soya agar with 2% NaCl at 25 ºC for 24 hrs were whitish yellow colour and circular. On thiosulfate citrate sucrose bile salt sucrose agar (TCBS) with 2% NaCl at 25ºC for 24 hour gave yellow colonies and some gave green colonies. The isolated bacteria were gram negative curved bacilli and motile ac alginolyticus, Vibrio anguillarum