原著論文 ORIGINAL PAPER

水田水域における淡水魚の双方向移動を保証する小規模魚道の試作と実験

鈴木正貴¹⁾・ 水谷正一²⁾・ 後藤 章²⁾

1)東京農工大学大学院連合農学研究科 〒１８３−８５３８ 府中市幸町３−５−８
2) 宇都宮大学農学部 〒３２１−８５０５ 宇都宮市峰町３５０

Masaki SUZUKI¹⁾, Masakazu MIZUTANI²⁾ and Akira GOTO²⁾: Trial Manufactures and experiments of small-scale fishways to ensure both upward and downward migration of freshwater fishes in the aquatic area with paddy fields. Ecol. Civil. Eng. 4(2), 163-177, 2001.

1) Doctoral Course in Agricultural Science, The United Graduate School, Tokyo University of Agriculture and Technology, 3-5-8 Saiwaicho, Fuchu 183-8538, Japan
2) Faculty of Agriculture, Utsunomiya University, 350 Minemachi, Utsunomiya 321-8505, Japan

Abstract:In 1999 the Environment Agency, Japan released the red list of brackish and freshwater fishes, in which the number of the Threatened fishes amounted to 110. One of the reasons why many fishes became endangered is implementation of land consolidation project in the paddy field area. This project aimed at reducing labor requirement in farming activities. However, watercourse networks have been disconnected by drop structures in the canals and elevation gap between outlets of paddy fields and drainage canals, which resulted in aggravation of the inhabiting environment of fishes. Therefore, it is eagerly required to reconnect watercourse networks by some artificial measures. In this connection this research was carried out to develop small-scale fishways for restoring damaged condition. In this research two kinds of fishes, Misgurnus anguillicaudatus and Oryzias latipes, were selected as sample fishes. Those are usual freshwater fishes in paddy field area of Japan, and Misgurnus anguillicaudatus represents a demersal fish, whereas Oryzias latipes represents a pelagic fish. Two types of small-scale fishways, named Cascade-M type and Chidori-X type, were developed and laboratory experiments were conducted to exam whether the developed small-scale fishways ensure upward and downward migration of sample fishes or not under the different conditions of inclination and flow rates. The result obtained were as follows ; 1） the Cascade-M type fishway enabled upward and downward migration of Misgurnus anguillicaudatus （crawling type and swimming type）, 2）Chidori-X type fishway enabled upward and downward migration of Misgurnus anguillicaudatus （swimming type） and Oryzias latipes, 3） Upward migration of Misgurnus anguillicaudatus became active in night time compared to day time, and 4） Oryzias latipes shows stronger rheotaxis compared to Misgurnus anguillicaudatus.

Key words: Japanese killifish, mud loach, migration, paddy field, small-scale fishway

摘要

環境庁が1997年に発表した汽水・淡水魚レッドリストに，絶滅危惧?類としてメダカが掲載されて話題となった．メダカは，河川（恒久的水域）と一時的水域（水田や小水路）の間を移動して，これらの水域を効果的に利用している．また，ドジョウなども同様な生活史を持つ．これらの生息数が減少している理由の一つとして，圃場整備事業があげられる．圃場整備事業は，農業従事者に対して作業時間の短縮や省力化といった様々な恩恵を与えている．一方で冬水の流水停止，水尻や排水路末端の落差形成など水域ネットワークを分断して，魚類の生息環境の悪化を招いている．そこで，工学的な手法による淡水魚類への配慮が求められるようになった．本研究は，水域ネットワークの再構築の一手段として小規模水田魚道の試作と実験を行ったものである．

2001年5月1日受付，2001年12月3日受理
1) e-mail: suzukim@env.mine.utsunomiya-u.ac.jp