pseudomonas fluorescens (Ps. fluorescens) strains recovered from diseased Oreochromis niloticus (O. niloticus) were studied for their pathogenicity, serum resistance activities and serological relatedness. The results of experimental pathogenicity in O. niloticus varied and generally ranged from acute septicaemic course to mild slow developing one or even none, suggesting the existence of variable virulence profiles among Ps. fluorescens strains, A correlation was foundbetween scrum resistance activity of Ps. fluorescens strains and their corresponding degrees of pathogenicity and virulence profiles as proved by the presence of a shared commonresistance to the killing effect of  O. niloticus sum among the highly  pathogenic virulent strains, In addition, heterogenecity among Ps. fluorescens strains was biochemically and serologically proved.