This study describes the aetiological agents of vibriosis outbreaks in cultured sea bass, Dicentrarchus labrax, L. from four different farms in the Aegean region of Turkey. Diseased fish were characterized by lethargie, exophthalmus, ulcers and skin lesions, haemorrhagies in the internal organs, ascites, paleness of kidney and liver. Morphological, physiological and biochemical tests were used to determine the phenotypic properties of pure cultures of isolated colonies in the samples taken from the internal organs and blood. Aquarapid-Va diagnostic kits and Mono-Va agglutination kit were also included in the study. The principal histological change was massive deposition of haemosiderin in the melano-macrophage centers in the spleen tissue.