The present study examined the effects of human chorionic gonadotropin (HCG ), salmon pituitary extract (SPE) and gonadotropin-releasing hormone agonist (GnRHa) administration on the sexual maturation of the male Japanese eel, using a newly introduced osmotic pump (OS ). The results showed that SPE and HCG , but not GnRH a, administration increased GSI values. The GSI values of fish that received HCG by OS were higher than those observed in the cholesterol pellet group and were similar to those observed in the injection group. The GSI values and milt volume of the eels significantly increased at a dose of 5 IU day-1 and up to 50 IU day-1 in a dose-dependent manner. From these results, we conclude that the HCG administration using OS is an efficient and reliable method for induction of spermatogenesis and spermiation in the male Japanese eel.