Immunohistochemical localization of LHR,ER and PR was performed using rabbit antiserum against leuteinizing hormone receptor (LHR or choriogonadotropin receptor CGR),estrogen receptor (ER) and progesterone receptor(PR).The aim of study was to reveal the endocrine mechanism of exogenous gonadotropin (CPE and hCG) inducing oogenesis and oocytes maturation in ovary of Japanese eel.The results showed that the ovary development and oogenesis in Japanese eel displayed very marked changes before and after hormones injection.The histological section showed at the early phase of vitellogenesis stage before hormone treatment,oocytes average diameter is about (220±0.01)μm,ten days after the first injection of the combination of two gonadotropins.It differed from control group,yolk nucleus scattered in the surrounding of nucleus and number of nucleolus increased obviously,about 18-20 nucleoli,and about 8-10 nucleoli in the control group..After the third and fourth hormones treatment,the oocytes entered in the early mid phase and middle phase of vitellogenesis stage and the number yolk granuleus was increased.After the sixth and seventh hormone treatment,the oocytes entered mature stage from midlate phase of vitellogenesis stage,the cytoplasm of oocyte were full of yolk granules,cellular diameter and nuclear diameter were increased,about (570±1.39)μm and (128±1.19)μm,respectively,while no change in the control group.At the same time,the staining results of immunohistochemistry showed that LHR,ER and PR were located on the cytoplasm,nuclear membrane,nucleoplasm,egg envelope and somatic cell.It was worth to note that localization characteristic of the three receptors after the third and furth hormone treatment,LHR immunoreactivity was located mainly in the cytoplasm of somatic cells(follicle cell at inner layer and thecal cell outside)of oocyte and showed strong immunopositive reaction,while ER and PR were located in the nucleus.Those results revealed that the endocrine mechanism of exogenous hormones (LH,FSH and hCG)inducing the development and maturation of oocyte in female eel were as follows:first, LH and hCG bound with LH receptor on the somatic cells,which stimulated somatic cells synthesis and secretion estradiol17β.Then,E₂ bound with its nuclear receptor in oocyte,stimulating growth and development as well as synthesis of yolk granules in the vitellogenesis stage oocyte.In addition,PR might mediate 17αhydroxyprogesterone in the gene effects of oocyte and its final maturation.For the first time,the present study would provide morphological demonstration.