Bull. Jpn. Soc. Fish. Oceanogr.  68(1), Page 1-8, 2004   Box-model Simulation for the Migration of Juvenile Shirauo (Salangichthys microdon) from the Main Stream to the Oxbow Lake in the Ishikari River Motohito Yamaguchi †1 and Takashi Fujioka2 Hokkaido Central Fisheries Experimental Station, 238 Hamanaka-cho, Yoichi-cho, Yoichi-gun, Hokkaido 046-8555, Japan. 1 Hokkaido Abashiri Fisheries Experimental Station, 1-1-1 Masu-ura, Abashiri, Hokkaido 099-3119, Japan.2 Hokkaido Institute of Mariculture, 539-112 Honbetsu, Shikabe-cho, Kayabe-gun, Hokkaido 041-1404, Japan. †e-mail: yamaguchim@fishexp.pref.hokkaido.jp *Yamaguchi M., S. Katayama and M. Omori (in preparation) Migration pattern of Shirauo, Salangichthys microdon, Bleeker in the Ishikari River system and adjacent nearshore sea area, Japan, as estimated by otolith microchemistry analysis. Numerical simulation was conducted to confirm two types of immigration mechanisms of juvenile Shirauo Salangichthys microdon to the oxbow lake through the Shibi Canal in the Ishikari River system. These mechanisms were consisted of three swimming behaviors of fish based on our survey in July 1995, 1996 and 1997. These behaviors, (1) coming near the bank during ebb tide, (2) moving away from the bank during flood tide and (3) staying around the mouth of the canal in the main stream of Ishikari River during ebb tide, were taken into the numerical simulation. Other passive movements of fish were dependent on water circulation. Through the calculation, some characteristics shown in the field survey were reproduced appropriately. It was suggested that staying around the mouth of the canal in the main stream of Ishikari River during ebb tide was more efficient to move to the oxbow lake. Key words: Salangichthys microdon, simulation of the migration, movement mechanism, the Ishikari River