Abstract: In order to determine the pathogen of Selenotoca multifasciata body rot disease, this study used plate streaking technology to isolate and culture a dominant strain of bacteria from the body rot disease lesions and viscera of Selenotoca multifasciata, named 5-2. The strain was identified based on colony morphology, physiological and biochemical characterization and 16S rRNA sequence analysis. Regression infection experiments and 7-day half-lethal concentration experiments were conducted to determine its pathogenicity. Finally, the infection route of this bacterium was explored using different challenge methods, and drug susceptibility testing was performed on the bacterium. The results showed that the isolated bacteria were Gram-negative, such as arc-shaped and rod-shaped. Based on its morphological characteristics, physiological and biochemical and 16S rRNA gene sequence analysis results, the pathogen was identified as Vibrio harveyi.After reinfection with this bacterium, the same symptoms as natural disease such as bulging eyes, body surface rot, tail rot, liver enlargement, and spleen congestion occurred. 7-day half-lethal concentration experiments showed that its 7-day half-lethal concentration was 5×10⁶ CFU·mL⁻¹. Experimental results of different infection routes show that the mortality rates associated with intraperitoneal injection, intramuscular injection, and high-density immersion are higher than those of other routes. Drug sensitivity test results showed that strain 5-2 was sensitive to 4 drugs including doxycycline, co-trimoxazole and florfenicol, and resistant to 4 drugs including kanamycin, cephalexin, cefradine, and ceftriaxone. The results of this study provide a theoretical basis for the prevention and control of body rot disease in Selenotoca multifasciata.