Bull. Jpn. Soc. Fish. Oceanogr. 68(2), Page 87-92, 2004   Movement of the juvenile shirauo (Salangichthys microdon) in a canal between the main stream of the Ishikari River and an oxbow lake Motohito Yamaguchi†1 and Takashi Fujioka2 Hokkaido Central Fisheries Experimental Station, 238 Hamanaka-cho, Yoichi-cho, Yoichi-gun, Hokkaido 046-8555, Japan 1 Hokkaido Central Fisheries Experimental Station, 238 Hamanaka-cho, Yoichi-cho, Yoichi-gun, Hokkaido 046-8555, Japan 2 Present address: Hokkaido Institute of Mariculture, 539-112 Honbetsu, Shikabe-cho, Kayabe-gun, Hokkaido 041-1404, Japan †e-mail: yamaguchim@fishexp.pref.hokkaido.jp Shirauo Salangichthys microdon inhabiting the Ishikari River hatched in the estuary during May and June, and migrated upstream on the salt wedge. It seemed that juvenile Shirauo moved to the oxbow lake through the Shibi Canal after reaching the mouth of the canal located 5.5 km from the river mouth in July. To reveal the immigration processes of juvenile Shirauo to the oxbow lake through the canal, water current and daily change in fish distribution in the canal were observed in July, 1995-1997. Vertical and horizontal distributions of juvenile Shirauo changed mainly with the flow directions and daily change, and two immigration processes were suggested from the changes of juvenile distribution. One process was that juveniles stayed around the canal mouth in the main stream during ebb tide, and they were carried to the oxbow lake by the fast flood tide in the deeper layer at center of the canal. The other process was that juveniles distributed near the bank in the canal to avoid the fast flow during the ebb tide and concentrated in the center with fast flow during the flood tide. These processes would be reasonable for immigration into the oxbow lake. Key words: Salangichthys microdon, migration, movement mechanism, the Ishikari River, oxbow lake