Since December 1961, the author investigated on Gnathostomas which lives in Ophicephalus argus, a fresh-water fish, from a standpoint of the epidemology.
The results obtained were as follows:
1) As distribution areas newly discovered basins of Nakiri-and Ikusue-river the middle and lower reaches of Kikuti-river, Tozin-river area, the lower reaches of Sirakawa and Tuboi-river, Ezu-lake, areas of Kase-, Kiyama- and Akai-river, and the lower and middle reaches of Midorikawa may be added.
2) The most numbers of Gnathostoma spinigerum Owen, 1836 detected in one-fish were 37.
3) The muscle was the part the parasite lived in all cases.