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6～8月にかけて主に沼田川中流域で採集したアユ30尾の耳石Sr/Ca比を調べ，由来判別を行った。その結果，30尾中12尾が天然遡上アユであることが判明した。また，支流の椋梨ダム湖（白竜湖）より上流の椋梨川で採集した13尾は，全ての個体で耳石Sr/Ca比の変動が認められなかったことから，これらはダム湖で再生産した陸封アユと考えられた。, Ayu, Plecoglossus altivelis altivelis, is a commercially important species of amphidromous fish. Thus it is being targeted for stock replenishment to sustain harvest numbers. Stock identification between amphidromous and hatchery fish was conducted using the otolith Sr/Ca concentration ratio on fish taken from the Nuta River in Hiroshima Prefecture, where 170,000 hatchery ayu had been previously released. Of 30 fish sampled from the middle-reaches, 12 were identified as an amphidromous form. Of the 13 fish sampled from the Mukunashi River, a branch of the Nuta River, all were identified as landlocked fish that would have completed their life cycle between the Mukunashi River and the artificial lakes formed by the Mukunashi Dam., 本研究は平成19年度広島大学地域貢献研究において，東広島市沼田川漁業協同組合より課題提案された「東広島市沼田川におけるアユの資源保全と有効利用」の一環として行った。

島根県江の川において産卵期のアユ42個体の由来判別を耳石Sr/Ca比を用いておこなった。放流実績からすれば江の川水系には天然アユの他,琵琶湖産,人工海産アユが生息している。産卵群42個体の由来を判別した結果,天然アユは13個体,人工海産が26個体となり,湖産アユは皆無であった。したがって,江の川においては湖産アユが海産系アユの産卵行動に関与している可能性は低いと考えられた。, Stock separation for spawning population of ayu Plecoglossus altivelis in the Gouno River was conducted using otolith Sr/Ca concentration ratio. Based on stock enhancement record, coexistence of amphidromus, hatchery-reared and landlocked ayu can be expected in the spawning population. In case of stock separation in the spawning population carrying out the otolith Sr/Ca ratio, 29 and 13 out of 42 individuals were categorized as the hatchery-reared and amphidromus ayu, respectively. The result of no landlocked ayu in the spawning population suggests that the contribution of the landlocked ayu to spawning and reproduction can be neglected at the Gouno River.