RESUMO
The present study was carried-out on naturally infected fish with Flexibacter columnaris. The number of fish examined were 100 fish collected from different farms of O. niloticus, Common carp, Clarias lazera in Behera, Kafr El-Sheikh and Alexandria Governorates. The clinical signs and Post mortem [P.M.] lesions includes erosions of jaws with congestion all over the body, haemorrhage and inflammation with darkening of body colour and enlarged, congested spleen and kidney. Trails for isolation of Flexibacter columnaris from different organs were made and we successfully isolate 4 strains grow on specific media [Ordal's] with yellow colonies, Gram negative short rods, non capsulated from [O. niloticus and Common carp] only. Biochemically it oxidase, ureas and indole negative, while, positive with glucose and maltose. Due to the morphological and biochemical characters of the isolates we identified it as Flexibacter columnaris especially the presence of rod like shape. The isolates were highly sensitive to antibiotics especially, Neomycin, Pencillin and Erythromycin