水田への魚類の遡上を促す遡上板の開発

Flashboards are set in the water outlets of paddy fields to manage water depth of the fields. Fish can enter paddy fields through the water outlets of the fields when water overflows due to rainfall and continuous irrigation. However, these flashboards often block fish migration. Therefore, we devised four types of migrating boards, namely, flat type, V-shape type, 5 mm guiding wall type, and 20 mm guiding wall type. These migrating boards cover the top of the flashboard and connect the water surfaces of paddy fields and the top pools of fishways. Upward migration tests on Carassius spp., Gnathopogon elongatus elongatus, Misgurnus anguillicaudatus, and Oryzias spp. were conducted using these boards. The highest number of fish migrated when using the 20 mm guiding wall type board. A total of 374 times of migration were observed for three of the four species; that is, migration was not observed for Oryzias spp., which was found to be unable to migrate probably due to the too strong currents for the species in these set-ups. The 20 mm guiding wall type migration board enabled smaller-sized fish to swim just inside the guiding wall and larger-sized fish to swim at the center of the guiding wall. Based on these observations, we concluded that the 20 mm guiding wall-type migrating board is the most effective in promoting fish migration.