Studies on EUS of freshwater fishes in Southeast Asia

1998 Fiscal Year Final Research Report Summary

• Project/Area Number: 08041159
• Research Category: Grant-in-Aid for international Scientific Research
• Allocation Type: Single-year Grants
• Section: Field Research
• Research Field: Applied veterinary science
• Research Institution: Nippon Veterinary and Animal Science University (NVAU)
• Principal Investigator: HATAI Kishio Nippon Veterinary and Animal Science University, Veterinary and Animal Science, Professor, 獣医畜産学部, 教授 (30164841)
• Co-Investigator(Kenkyū-buntansha): KURATA Osamu Nippon Veterinary and Animal Science University, Veterinary and Animal Science,, 獣医畜産学部, 助手 (90277666) ; WADA Shinpei Nippon Veterinary and Animal Science University, Veterinary and Animal Science,, 獣医畜産学部, 講師 (90220954)
• Project Period (FY): 1996 – 1998
• Keywords: Southeast Asia / freshwater fishes / epizootic ulcerative syndrome (EUS)

Research Abstract

Mycological and histopathological studies of diseased fishes with epizootic ulcerative syndrome (EUS) were conducted in Thailand, Philippines and Bangladesh for the term of this project. One hundred and twenty nine samples were collected during this period. Fungal isolation was attempted from external ulcerative lesions in 113 of 129 samples, and 5 and 2 isolates belonging to the genera Aphanomyces and Achlya were obtained, respectively. The biological characteristics of the present strains, Aphanomyces spp. from EUS lesions were quite similar to those of the causative agent of mycolic granulomatosis, Aphanornyces piscicida, isolated from cultured ayu in Japan. Furthermore, two of these Aphanomyces isolates showed apparent pathogenicity to goldfish by artificial infection test. On the other hand, two isolates of the genus Achlya from samples in Thailand were identified as a new species, Achlya siamensis sp. nov., which was the first scientific report of a new species of the genus Achlya from Thailand.
Histopathological examination was performed on 120 of 129 samples. As a result, 38 samples possesed fungal lesions characterized by penetration of abundant branching, aseptate hyphae1 from epidermis to muscle layer associated with epitheliold cell granulomas around them. ln some cases, small numbers of giant cells were also present in the lesions. These histopathological features corresponded to those of mycotic granulomatosis case in ayu, goldfish and some other wild fishes in Japan.
From the results mentioned above, we concluded that EUS could be classified into the same disease group as mycotic granulomatosis, and the very obscure name " EUS" should be revised as mycotic granulomatosis. In addition, we can strongly recommend the adoption of Aphanornyces piscicida, the earlier published (in 1980) scientific name of the causative fungus of this disease group including EUS and mycotic granulomatosis, rather than Aphanomyces invadans published in 1997.