The initial ovarian development of ricefield eel Monopterus albus raised under laboratory conditions was investigated with histological analysis,and the expression of gdf9(growth differentiation factor 9),cyp19a1a (P-450 aromatase),amh(anti-M?llerian hormone)and amhrII(anti-M?llerian hormone type II receptor)was analyzed with Real-time PCR assay.From the age of 4 months to 9 months,the oocytes in the ovary of juvenile ricefield eel remained in the primary growth stage,and the basophilic Balbiani’s vitelline bodies(Bb)increased in number at the beginning,then decreased,and Bb’s shape changed from dot at first to large cluster,then to small cluster.At the age of 10 months,the oocytes in the ovary of the juvenile ricefield eel entered the secondary growth stage,with the appearance of cortical alveoli in the cytoplasm and the differentiation of the somatic cells around the oocyte into granulosa and theca cells,and Bb either disappeared or degenerated to dot,indicating that the ovarian puberty of the juvenile ricefield eel was initiated.At the age of 12 months,the ovary of the ricefield eel was filled with late vitellogenic oocytes containing migratory or disintegrated germinal vesicles,and reached maturity.The expression ofgdf 9 was high and did not vary significantly from the age of 4 to 12 months,suggesting its indispensable roles in ovarian development during this period.The expression levels of amh,amhrII,and cyp19a1a increased in ricefield eels at the age of 4 to 7 months,but decreased at 8 months.However,the expression of these genes increased at the age of 10 months,coinciding with the initiation of puberty.Taken together,the results of present study indicated that juvenile ricefield eels initiated ovarian pubertal development at the age of ten months,and might reach ovarian maturation at the age of one year.The expression of amh,amhrII,and cyp19a1a might play important roles in the initiation of ovarian puberty.