山形県最上川水系小国川の支流である大横川で採集したヤマメOncorhynchus masou masou (Brevoort, 1856)の鰾と,島根県益田川で採集したヤマメの鰾から,マスウキブクロセンチュウ(鱒鰾線虫)Salvelinema salmonicola (Ishii, 1916)を得た。本線虫は両県から初記録である。Specimens of the cystidicolid nematode Salvelinema salmonicola (Ishii, 1916) were collected from the swim bladder of river-resident masu salmon, Oncorhynchus masou masou (Brevoort, 1856), in Yamagata and Shimane prefectures, Honshu, Japan. This nematode is reported herein for the first time from these two prefectures in Japan