Controlled reproduction in the Japanese eel (Anguilla japonica), past and present

The Japanese eel, Anguilla japonica, is one of the most important species of the aquaculture industry of East Asia. Supply of glass eels for aquaculture is completely dependent on wild catch. However, glass-eel catches in Japan declined linearly from over 200 tons in the early 1960s to 20 tons at present. In recent years an unstable situation has occurred with glass-eel catches not meeting the demand of aquaculture farms. In order to address this rapid decline, a challenging research project for artificial production of glass eels was commenced in the late 1960s. Since then, through a continuing process of trial and error, the production of second-generation larvae was finally achieved in 2010. Throughout the research, a new application of several substances has caused breakthroughs in artificial induction of sexual maturation and larvae rearing. This article reports on a study of controlled eel reproduction focusing on the finding of substances that accelerated progress. In addition, guideline research on eel reproduction in the wild was conducted aiming at overcoming current bottlenecks that impeded the establishment of largescale glass-eel production in captivity, by investigating maturing eels and eggs collected in their spawning area in the vicinity of the West Mariana Ridge.