Studies on the reproduction mechanism in the Japanese eel inferred by DNA analysis and otolith microchemistry.

1.群体结构分析：通过对同一年在中国台湾、种子岛和宫城县采集的总共200条玻璃鳗的线粒体DNA控制区的核苷酸序列（近600 bp）进行分析，没有发现群体间遗传分化的证据。同样的情况下，leptocephali样品，这可能反映了产卵聚集体的遗传特征。为了在核DNA水平上更详细地研究玻璃鳗的遗传结构，对来自宫城、神奈川和种子岛的30条玻璃鳗进行了扩增片段长度多态性（AFLP）分析，也没有显示明显的地理分化。总之，目前对玻璃鳗和细头鳗的DNA分析没有为日本鳗种群的遗传分化提供任何证据。耳石显微结构分析：对日本5个地区的150尾玻璃鳗在渔季初、中、末期的耳石分析揭示了玻璃鳗的一种补充机制：产卵期较早出生的个体往往较晚出生的个体更早地向低纬度的东亚河口进行补充，年龄较小，生长速度较大。通过耳石Sr的EPMA分析，在日本和中国东海沿岸沃茨采集的银鳗中，约有75%为从未洄游到淡水中的海鳗，这表明日本鳗的繁殖可能主要依靠这种海鳗.结论：日本鳗鲡的大规模繁殖表明东亚四国对玻璃鳗渔业进行了国际管理。此外，河口作为鳗鱼栖息地的重要性，建议保护该地区的环境和成年鳗鱼，以保护鳗鱼资源。

1. Analysis of population structure : Population structure analysis through examination of nucleotide sequences (nearly 6O0bp) of the control region in the mitochondrial DNA from a total of 200 glass eels collected in the same year at Taiwan, China, Tanegashima, and Miyagi Prefecture provided no evidence for genetic differentiation among populations. The same was the case for leptocephali samples, which might much reflect genetic characteristics of spawning aggregates. In order to examine genetic structure of glass eels much in detail in the nuclear DNA level, amplified fragment length polymorphism (AFLP) analysis was made for 30 glass eels collected from Miyagi, Kanagawa, and Tanegashima, and also showed no clear geographic differentiation. Altogether, the present DNA analyses of glass eels and leptocephali did not provide any evidence for genetic subdivision of Japanese eel population.2. Analysis of otolith microstructure : Otolith analysis of 150 glass eel collected from five localities in Japan at the beginning, mid and end of fishing season revealed a recruitment mechanism of glass eel : the individuals born earlier in the spawning season tended to recruit earlier to the East Asian estuaries in the lower latitude with the younger age and the larger growth rate than those born later. From EPMA analysis of otolith Sr, about 75% of silver eel collected in the coastal waters of Japan and East China Sea was estimated as sea eel that had never migrated into freshwater, suggesting that reproduction of the Japanese eel might be supported mostly by such sea eel.3. Conclusion : A possible large panmictic population of the Japanese eel suggested a international management of glass eel fishery among four countries in Ease Asia. Furthermore, the importance of estuaries as an eel habitat suggested the protection of the environment of this area and the adult eel to conserve the eel resources.