Study on the Pathogenic Fungus of Mycotic Granulomatosis—I

An epizootic of mycotic granulomatosis occurred among pond-cultured ayu, Plecoglossus altivelis at a fish farm in Shiga Prefecture. A fungus was isolated by inoculating materials taken from lesions of diseased fish onto FME agar and incubating at 25°C (Table 1).Inoculation experiments using ayu and gold fish, Carassius auratus showed that the fungus was the causative agent of mycotic granulomatosis. The experiments were done by injecting a mass of hyphae cultured on the FME agar into intramuscularly each fish. Granulomatosis was histopathologically demonstrated in all the artificially infected fishes, from which the fungus was reisolated by means of inoculating materials from lesions on FME agar.Spore formation was not observed in the fungus growing in the lesion of naturally infected ayu, and the source of infection of mycotic granulomatosis was thought to be hyphae themselves.The present authors suggest the temporary designation, MG-fungus (Mycotic Granulomatosisfungus), until the fungus is named.