Contributing Factors to Tural Fish Reproduction in the Rice Paddy With Fish Pass

27 Mar Contributing Factors to Tural Fish Reproduction in the Rice Paddy With Fish Pass

View Original

Abstract

7月の六方たんぼの魚道付き水田は，ドジョウ，ナマズおよびフナ属の産卵，生息場所として機能しており，それらを捕食する可能性が高いカエル類幼生，水生昆虫類も同所的に生息していた．捕獲された魚類は99％が当歳稚魚であり，ナマズは産卵遡上群が複数存在することが示唆された．水田間の魚類現存量は大きく異なり，それに寄与すると考えられる4つの要因が抽出された．物理要因としては，1：水田の水深， 2：幹線排水路（ソース）からの距離があげられた．一方，生物的要因としては，3：カエル類幼生および 4：水生昆虫の密度があげられた．特に魚類が確認されなかった水田のカエル類幼生の生息密度は11.8個体／m2と大きく，それらによる魚類受精卵や稚魚の捕食の影響は大きいことが考えられた．魚道付き水田における魚類再生産の成功程度に関しては，前述の生物的要因やソース（魚類の遡上元）からの距離等を含めた多要因からの検討は行われていない．したがって今後は，それらに着目した研究を多地点で実施し魚類再生産に与える決定要因を明らかにする必要がある．

English Abstract

tural fish reproduction in three rice paddies with fish pass was investigated in Roppo rice field in Toyooka City, Japan. Re-introduction project of endangered Oriental White Stork has been promoted in Roppo rice field since 2007. These paddies mainly served as habitat for fishes such as loach, catfish and Carassius sp. Tadpoles and aquatic insects, which may preyed on fertilized eggs and fish larvae, were also present in the paddies. Based on histogram, 99％ of the captured fishes were observed at larval stage. Two spawning groups of catfish also existed in the paddies. The fish density in the rice paddies were greatly affected by water depth in the rice paddy, distance from the main ditch which functioned as fish source, and density of tadpole and aquatic insect. Further research focusing on critical factors, which contribute to tural reproduction in the paddy with fish pass, particularly biological relationship should be conducted.