Early life history of Japanese eel inferred by otolith microstructure

为了确定日本鳗鲡的早期生活史，对日本鳗鲡耳石的显微结构和微化学进行了研究。结果表明：1991年在菲律宾海（15 ° N，137 ° E）产卵区附近采集的日本鳗鲡幼鱼的孵化时间呈双峰分布，间隔2周，表明该鱼种为单卵产卵。2.人工采得的幼鱼孵化检查直径（9 μ m）小于野生样品（12 μ m），表明野生样品的孵化时间（40小时）长于人工养殖的幼鱼。3.耳石微量元素的ICP法测定结果表明，鳗鲡耳石中Ca、Sr、Zn、Fe、Mg、Mn、Al等元素含量较高。Ca含量最高（40%），Sr含量次之（0.1-0.3%）。Sr含量随物种的不同而变化，淡水鱼约为0.1%，海水鱼为0.2%，而在洄游鱼类中为中间值。另一方面，在Danjyo Gunto Is取样的鳗鱼。在东海，除耳石中部外，整个耳石区域均呈现高Sr浓度。基于Sr含量的差异，这表明，这些样品的环境水之间的海水和淡水，没有显示出一个普通的迁移模式，但仍然在海水中孵化后。

To determine the early life history of the Japanese eel, otolith microstructure and microchemistry were investigated. Results obtained are follows :1.Birthdate of the Japanese eel leptocephali sampled near the spawning area (15ﾟN,137ﾟE) in the Philippine Sea 1991 showed a bimodal distribution with 2 weeks interval suggesting that this species spawn periodically.2.Hatch check of artificially obtained larvae was smaller (9mum) in diameter than that of wild specimen (12mum), which suggested that the wild had a longer incubation time than the reared fish (40hrs). The wild also had some embryonic rings (1-6), while the reared had no ring.3.Observation of otolith microelements by ICP method detected Ca, Sr, Zn, Fe, Mg, Mn, Al in sagitae of the eel. Ca content was highest (40%), and Sr was the next (0.1-0.3%) contents of Sr varyed among species corresponding to their migratory pattern ; freshwater fishes was about 0.1%, marine fishes 0.2%, and their intermediate values in diadromous fishes.4.Fluorescent X ray Imaging by syncrotoron showed that the eel otolith generally had a hight concentration of Sr at otolith core. On the other hand, the eels sampled at Danjyo Gunto Is. in the East China Sea showed a high Sr concentration at not only central part but also whole area of the otolith. Based on the difference in Sr content this suggested that these specimens of ambient water between seawater and freshwater, did not show an ordinary migratory patterns, but remained continuously in the sea water after hatching.