Abstract: The effects of 4-androstene-3,17-dine (ADSD) and 17α-methyl-testosterone (MT) via implantation at intervals of 15 days on maturation of the male silver eel,and their effects on brain and pituitary GnRH levels,pituitary and serum GtH levels were studied.Multiple implantations of ADSD and MT increased the GSI and stimulated gonadal maturation of the male silver eel.After 3 im plantations,the GSI of males treated with MT were significantly higher than that treated with ADSD,whereas after 6 implantations their GSI were not significantly different.The mGnRH contents in the brain and pituitary were significantly increased after 3 and 6 implantations of ADSD and MT,and the mGnRH contents were elevated with increasing times of implantations.The pituitary GtH levels of male eels wer significantly increased by multiple implantations of ADSD and MT,and after 3 implantations the pituitary GtH level of MT-treated male eels was significantl higher than that treated with ADSD.Serum GtH levels of MT-treated male eels were increased significantly after 1st implantation,however,serum GtH levels in the male eel treated with ADSD were significantly increased only after 4 implantations.Taken together,these results indicated that ADSD and MT could stimulate gonadal development and had positive feedback effects at the brain and pituitary in the male eel,and the higher potency of MT in the induct ion of gonadal development maybe due to its higher ability to stimulate GtH synt hesis and release in the male eels.