Mycobacteriosis in the Captive Japanese Rosy Bitterling (<i>Rhodeus ocellatus kurumeus</i>) Caused by <i>Mycobacterium marinum</i> Infection

Here we report on mycobacteriosis in a captive population of an endangered fish species, the Japanese rosy bitterling (Rhodeus ocellatus kurumeus), reared in Japan. In 2004, some of these fish began to show reddening and ulceration on the body surface, and scale elevation. The spleens of diseased fish exhibited white nodules of various sizes. Apparent swelling of the trunk kidney was also seen in some cases. The most prominent histopathological characteristic was the presence of granulomas, which comprised epithelioid cells, in the head and trunk kidney, spleen, heart, intestine, peritoneum, liver, gills, trunk muscles, eyes and optic brain. Numerous colonies of long and slender acid-fast rods were observed within the granulomatous lesions. The bacterial strain was identified as Mycobacterium marinum.