Migration history of fishes inferred from otolith microchemistry including oxygen isotopic composition and Sr : Ca ratio

本研究的目的是从耳石的微观结构和微观化学，包括氧同位素组成和锶/钙比，来研究鱼类的迁徙历史。证实了二次离子质谱仪(SIMS)是分析鱼耳石氧同位素的有效方法。通过检测伴随着耳石日轮的氧同位素组成，重建了鱼类个体经历的水温变化。[氧同位素组成]玻璃鳗(日本鳗)耳石用于氧同位素检测。每个耳石都被接地，以暴露耳石核心。接地耳石表面的光滑处理对SIMS分析的准确性至关重要。对耳石的氧同位素组成进行了研究，包括耳石核心和周围区域。其比值(^&lt；18&gt；O/^&lt；16&gt；O)在耳心高于周围其他区域，表明鳗鱼的产卵温度低于仔鱼暴露的温度。鳗鱼可能会在产卵区的更深水域产卵。[耳石锶钙比]对日本沙丁鱼和两栖鱼的耳石进行了锶：钙的测定。日本沙丁鱼耳石锶钙比的变化不伴随水温和盐度的变化，提示耳石锶钙比不能用于研究日本沙丁鱼的迁移史。相反，该比率较好地再现了两栖鱼类个体的分布环境(即海洋、浅滩、淡水)的变化。这对区分两栖和非两栖放养鱼类是有用的。

Objectives of this study were to examine fish migratory history from otolith microstructure and microchemistry including oxygen isotopic composition and Sr : Ca ratios. We confirmed that secondary ion mass spectrometry (SIMS) was useful methodology to analyze oxygen isotopes of fish otolith. The changes in water temperature that fish individual experienced is reconstructed by examine oxygen isotopic composition accompanied with otolith daily rings. [Oxygen isotopic composition] Glass eel(Japanese eel)otoliths were used for this oxygen isotopic examination. Each otolith was grounded to expose the otolith core. The smoothing of grounded otolith surface was very critical for the accuracy of SIMS analysis. The oxygen isotopic composition was examined on the otolith including otolith core and surrounding regions. The ratio (^<18>O/^<16>O) was revealed to be higher in ototith core than the other surrounding region, suggesting that spawning temperature of eels was lower than that the larvae exposed. Eels may spawn in deeper waters in their spawning area. [Otolith Sr : Ca ratios] Otolith Sr : Caratios were examined on otoliths of Japanese sardine and ayu (amphidromous fish). Changes in otolithSr : Ca ratios were not accompanied with changes in water temperature and salinity in Japanese sardine, suggesting that otolith Sr : Ca ratio was not useful for investigating the migration history of Japanese sardine. In contrast, the ratio well reconstructed the changes in distribution environment (i.e. sea, brakish, freshwater) in amphidromous ayu individuals. And it was revealed to be useful to distinguishing between amphidromous and non-amphidromous stocked fish.