STUDIES ON THE BREEDING BIOLOGY OF THE EEL(ANGUILLA JAPONICA TEMMINCK SCHLEGEL)V. Effects of sex steroids on gonadotropin synthesis and secretion, as well as ovarian devel-opment in female silver eel.

The effects of sex steroids on gonadotropin(GtH)synthesis and release as well asovarian development in female silver eels were investigated.Multiple injections of17β-estradiol or testosterone stimulated GtH synthesis and secretion as well as ovarian development; testosterone was more effective than estradiol in this respect.Multiple injectionsof LHRH-A were ineffeetive on pituitary GtH content and ovarian development.Multipleimplantations of l7β-estradiol or testosterone stimulated the increase n pituitary GtH content,but no significant changes in serum GtH levels were detected at the samplingtimes.M ultiple implantations of 17β-estradi ol resulted in a marked increase in serumvitellogeain content,but ovarian development was not significantly stimulated,multipleimplantations of testostero ne were e ffective in stimulating an increase in ovariandevelopment,although there were no significant differences in the serum vitellogenin levelwhen compared with the controls.Multiple implantations of testosterone in combinationwith LHRH-A did not stimulate further increase in pituitary GtH content or ovarian development.In a given duration of experiment,the effects of multiple implantations oftestosterone in stimulating ovarian development were similar to those of multiple injections oftestosterone.These results demonstrate that serial implantations of testosterone alone canstimulate the brain-pituitaryovary axis of the eel to enhance GtH synthesis in the pituitaryand to induee ovarian development.