الفهرس 
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Abstract
Randomly 280 fish Mugil cephalus, Rastrelliger kanagurta, Nemipterus japonicas and Sparus aurata samples were collected from Ataka fishing port, Suez-bay, Suez Governorate( 70 samples in winter and fall and 140 samples in spring), some fishes showed hemorrhage all over the body surface including gills cover and fins, scales detachment accompanied by slight swelling of abdomen. Target organs of isolation were gills, liver, kidneys and intestine. Enrichment and isolation on Tryptone Soya Agar medium and X.L.D medium. Morphological and biochemical identification of bacterial isolates revealed three different isolates of Edwardsiella tarda named in this study (A),(B) and (C) their diagnosis was confirmed using 16S RNA gene for PCR, their virulence was differentiated by H2S, Indole, Catalase test and haemolysis on blood agar (α, β and γ). The total prevalence of E. tarda isolates was (11.1%) among the examined marine fishes while seasonal prevalence was (17.9%) in spring, (2.9%) in winter and (5.7%) in fall. The LD50 was 2X106 CFU/ml for (A) and (B) isolates and 2X107 CFU/ml for isolate (C). Mortality rate for the experimentally infected Cyprinus carpio for isolates (A), (B) and(C) were 70, 80 and 50% respectively. Histopathologically necrosis and degeneration found in gills, liver, kidneys and spleen.