The aim of this study was to identify the most important growing, morphological and biochemical characteristics of two bacteria from the genus Vibrio; Vibrio anguillarum and Vibrio harveyi for early detection of vibriosis in farmed sea bass. During the studies carried out for this thesis we used standard bacteriological methods, but in order to confirm that isolated DNA belonged to bacteria V. anguillarum and V. harveyi we also performed a molecular identification using the polymerase chain reaction. From sick fish we isolated 6 strains of V. anguillarum and 6 strains of V. harveyi, and we compared their morphological and biochemical characteristics. To create the basis for successful treatment and prevention of vibriosis in farmed sea bass, we tested a sensitivity of each isolated bacteria to a certain antibacterial substance. Results showed that most often the disease appears in its acute or subacute course, characterised by hemorrhages around the mouth, on the fins basis and perianal region. Comparing biochemical properties of isolated bacterial strains of V. harveyi to V.anguillarum we concluded that the first ones do not have abillity to utilize galactosidase, to decompose tryptophan into indole, have no mechanism of degradation of gelatine and do not produce nitrates and acetoin. It is proved that all the strains are sensitive or moderately sensitive to low concentrations of flumequine, oxytetracycline, oxolinic acid and trimethoprim-sulfamethoxazole. This study provided basis for faster diagnosis and successful treatment of vibriosis.