The Japanese eel, Anguilla japonicu is a commercially important cultured species in Asia contries. Eel are catadramous, It spawn in the Pacific Ocean and the larvae migrate to estuaries. Most glass eel migrate upstream and grow in freshwater numberous years until maturation. But the ages at migration and growth rates for mature eel in river has been rearly studied. The object of releasing program for broodstock eel is necessary for not only the natural elver resources but also spawning migration research of matrue eel.