Abstract
Bacterial infections are among the major factors reducing survival and productivity of sturgeon in aquaculture, particularly in recirculating aquaculture systems. The relevance of this study is determined by the need for timely detection of opportunistic bacteria that may cause fish diseases and spread under intensive farming conditions. The study aimed to isolate and characterize Pseudomonas and Aeromonas bacteria associated with bacterial diseases of sturgeon fish. Siberian sturgeon (Acipenser baerii) and sterlet (Acipenser ruthenus) with ulcerative skin lesions were used as study material. Swab samples were collected from affected sites, and pathological examinations were performed. Two pure bacterial cultures were obtained after successive subculturing. The isolates differed in colony size and colour but showed similar cultural characteristics. Gram staining and biochemical tests characterized the cultures as motile Gram-negative rods with positive oxidase activity, glucose oxidation, and arginine decarboxylase activity. The findings confirm the need for regular microbiological surveillance in industrial sturgeon-rearing systems to support early disease diagnosis and prevent the spread of bacterial infections.