Bacteriophages are an important driving force for bacterial evolution. Several reports suggest that lytic bacteriophages are a selective pressure permitting the proliferation of bacteriophage-resistant mutant strains with reduced virulence. The aim of this study was to explore the role of the bacteriophage CHOED, which has been successfully used to prevent vibriosis in Salmo salar, in the diversification and virulence of the host bacteria V. anguillarum. CHOED was used to isolate 61 constantly resistant strains of V. anguillarum. All the strains were analyzed in their motility revealing that 39 strains present a reduction of more than 50% in their motility. 9 strains were selected according to these results and were analyzed in different phenotypic characteristics related to virulence. None of the selected strains presented differences in their LPS and OMPs profiles, nor in their haemolytic or protease activity. However the strains R28, R36 and R72 presented a reduction in their growth and the strains R5, R7, R14 y R28 presented an increase in the biofilm production. The biochemical profile using the BIOLOG GEN III system revealed several alterations in the resistant strains compared to the parental strain; however there is no evident biochemical pattern followed by all strains. A virulence assay using gilthead seabream larvae model showed that the strain R72 presented a marked reduction in virulence, while strains R14 and R36 have not alteration compared to the parental strain. The strains R5, R6, R7, R22, R28 and R78 also present a lower virulence than the parental strain; however remains more virulent than strain R72. These results suggest that bacteriophage resistance is not necessarily associated to virulence reduction since the selected strains presented different phenotypes and virulence grades. The bacteriophage CHOED is probably acting as a selective pressure for V. anguillarum in a natural process of diversification through spontaneous mutations.