Bacterial pathogens are major etiology of infectious diseases of fish. In this study we were isolated and identified the most important Gram negative bacteria as Aeromonas spp,Coliforms.,Salmonella spp.,Pseudomonas spp.,Vibrio spp.from gills,skin,intestine,kidneys of diseased fish mainly in Tilapia niloticus and environmental water at Mahmoudia canal in Elmahmoudia city,Edfina city and spans as abrakish water,and assessment of genetic and biochemically relatiotions of the prominent bacterium. Bacteria as Aeromonas spp,Coliforms.,Salmonella spp.,Pseudomonas spp., were identified phenotypically,except V.parahaemolytica spp which was the prominent bacterial species isolated was confirmed moleculary by PCR,typed it’s strains from fish and water by ERIC_PCR.inorder to answer the question wither Vibrio spp infiction considered water borne disease or not.Unfortionately ERIC_PCR nor answered as the bacterium have diverse genetic heterogenus where the isolated were similar but genetically differed . However.in most cases, the origin of the infiction is suspected to be environmental due to phenotype similarity of isolates . The aim of this study was to investigate similarity of certain bacteria in clinically diseased fish and environmental water.