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<p>The Japanese eel early juveniles, called glass eels, are caught for use in aquaculture, but their catches have decreased and recruitment levels fluctuate from year to year. To better understand the recruitment pattern of the glass eels, we conducted monthly sampling of <i>A. japonica</i> glass eels at the estuary of the Kiyotake River in Miyazaki of southern Japan for 12&#xa0;years from November 2011 to July 2022. According to previous sampling in rivers and otolith studies of <i>A. japonica</i> glass eels, this species appears to hatch out during April–December with a peak in August in the ocean and enters the freshwater areas during October–April with a peak in November–March. However, the 12-years of glass eels sampling in this study found that the highest peak of the catch per unit effort (recruitment) occurred in May and June in 2012, 2018, 2020 and 2021. Otolith observations of the glass eels collected in May and June revealed that they had hatched out in November–January. Contrary to the previously published information, we found the late hatching dates and late arrival of glass eels of the Japanese eel. Their seasonal shifts of arrival and hatching suggest that changes in the reproductive traits of adult spawners might be occurring.</p>

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Late hatching and arrival of Anguilla japonica glass eels collected from the Kiyotake River in 12 sampling years

  • 期刊论文

  • 发表日期：

    2025年8月27日

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  • Aya Takeuchi,
  • Kodai Miyatake,
  • Takatoshi Higuchi,
  • Mari Kuroki,
  • Shun Watanabe

摘要

The Japanese eel early juveniles, called glass eels, are caught for use in aquaculture, but their catches have decreased and recruitment levels fluctuate from year to year. To better understand the recruitment pattern of the glass eels, we conducted monthly sampling of A. japonica glass eels at the estuary of the Kiyotake River in Miyazaki of southern Japan for 12 years from November 2011 to July 2022. According to previous sampling in rivers and otolith studies of A. japonica glass eels, this species appears to hatch out during April–December with a peak in August in the ocean and enters the freshwater areas during October–April with a peak in November–March. However, the 12-years of glass eels sampling in this study found that the highest peak of the catch per unit effort (recruitment) occurred in May and June in 2012, 2018, 2020 and 2021. Otolith observations of the glass eels collected in May and June revealed that they had hatched out in November–January. Contrary to the previously published information, we found the late hatching dates and late arrival of glass eels of the Japanese eel. Their seasonal shifts of arrival and hatching suggest that changes in the reproductive traits of adult spawners might be occurring.