Mycobacterium marinum is a well-recognised mycobacterial species which produces granulomatous reactions in a variety of aquatic organisms. Detection of this organism primarily relies on histological and bacteriological examination of infected fish tissues but recently a number of molecular methods have also been employed. In this study a comparison of three such methods in the detection of M. marinum in goldfish (Carassius auratus) was carried out. Histological analysis revealed that fish infected with M. marinum often developed granulomas in the absence of external lesions and clinical signs of mycobacteriosis. Approximately 40% of all infected fish had greater than/equal to 104 mycobacteria per gram of splenic tissue. Approximately 89% of samples (8/9) with < 104 CFU/g of spleen were positive by PCR. Statistical analysis revealed significant differences between the 3 methods of comparison for the entire sample (N = 15), but very significant differences between PCR and other detection methods (p = 0.0202). Overall, this study demonstrates that PCR is a rapid, specific, and sensitive method for detecting M. marinum in goldfish.
