A visceral mycosis in cultured masu salmon (Oncorhynchus masou) caused by a species of Ochroconis

Ochronconis sp. infection was found in masu salmon (Oncorhynchus masou) with visceral mycosis in Japan. The external and internal clinical signs were reddening of the anal area, swelling of the abdomen due to accumulation of ascitic fluid in the abdominal cavity and extensive swelling of the posterior kidney. Many pale brown, septate hyphae were found in the kidney by direct microscopical examination; these were usually not found in the other organs of infected fish. Histopathological examination of the kidney revealed large granulomas with the fungal hyphae and giant cells. The isolated fungus was identified as a species of the genus Ochroconis and was compared with O. tshawytschae, a known fish pathogen. Based on morphological and growth characteristics, we believe that these cases resulted from infection with a different species.