Role of puberty in the migration initiation mechanism of the Japanese eel

2022 Fiscal Year Final Research Report

• Project/Area Number: 19K15900
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 40030:Aquatic bioproduction science-related
• Research Institution: The University of Tokyo
• Principal Investigator: Hagihara Seishi 東京大学, 大気海洋研究所, 特任講師 (80704501)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Keywords: ウナギ / 銀化 / 産卵回遊 / 降海回遊 / 性成熟 / 春機発動 / 意思決定機構 / 個体差

Outline of Final Research Achievements

We investigated the reproductive physiological characteristics of pre-silver and non-pre-silver eels in summer through rearing experiments in a large outdoor experimental pond that simulates the natural environment. The results revealed that eels, which begin silvering and migrating in the fall, began puberty already in early summer.
Then, wild female eels were collected and analyzed in summer. Pre-silver eels showed higher body condition and significantly higher lipid content in the muscle than non-pre-silver eels. Ovarian histology revealed that pre-silver eels accumulated oil droplets in the oocytes to promote oogenesis. In addition, blood 11-ketotestosterone (11-KT) levels in pre-silver eels were significantly higher than in non-pre-silver eels.

Free Research Field

生理生態学

Academic Significance and Societal Importance of the Research Achievements

回遊を開始する体サイズと年齢は個体変異に富み、どんな生態学的条件を満たした個体が、どのような生理学的プロセスを経て、春機発動・銀化・回遊開始に至るかは明らかでない。これを解明すれば、ウナギの生殖生理と回遊現象の理解を大きく深めることができる。
本研究の結果から、秋に銀化して回遊開始するウナギは、少なくとも初夏の時点で春機発動が生じている個体と考えられた。これは、銀化などの回遊関連の形態的・生理的変化は水温が低下する秋に生じるという従来の常識を覆すものである。
春機発動と銀化の生理生態学的機構が明らかになれば、人為催熟技術の改善に資する有用な知見にもなり得る。