Mycobacterium marinum and Mycobacterium fortuitum infections in Siamese fighting fish, Betta splendens (Regan), in Thailand

Mycobacterium marinum and Mycobacterium fortuitum are important causative agents of mycobacteriosis in fish worldwide. Moreover, M. marinum can cause granulomatous skin lesions in humans. The objectives of this study were to determine the prevalence of Mycobacterium infections in Siamese fighting fish, Betta splendens (Regan), in Thailand and to evaluate the pathogenicity of the Mycobacterium isolates in goldfish. In the prevalence study, 190 Siamese fighting fish (15 moribund and 175 clinically healthy fish), collected from culture farms and ornamental fish markets in Thailand, were included and examined. Mycobacterium spp. were isolated from the kidneys, spleen, liver and gills. The isolates were then identified on the basis of morphological, biochemical characteristics and the analysis of a partial 16S rRNA gene sequence. The prevalence of Mycobacterium infections in this study was 15/15 (100%) in the moribund fish and 50/175 (25.71%) in the clinically healthy fish. In the pathogenicity study, 150 clinically healthy goldfish were used to test for the 2 isolates (Mycobacterium marinum KKVB0901 and Mycobacterium fortuitum KKVB0926). Results from the test showed that both isolates were pathogenic to experimental goldfish.