ARTIFICIAL INDUCTION OF GONADAL MATURATION AND OVULATION IN THE JAPANESE EEL (ANGUILLA-JAPONICA T ET S.)

8 injections of carp pituitary extract (CPE, 5 pit./fish/10 days) indu ced ovarian maturation in female eel, gonadosomatic index (GSI) increa sing significantly to 43-55%. 4 injections of CPE (1-2 pit./fish/10 da ys) induced spermatogenesis and spermiation in male eel, GSI increasin g to 2.1-2.8%. After serial injections of CPE, serum gonadotropin (GtH ) levels increased significantly, indicating that the exogeneous GtH s timulated gonadal development and maturation in the Japanese eel. 8 im plantations of 17 alpha-methyltestosterone (MT) or androstenedione (AD SD) (50 mu g/g body weight/15 days) stimulated ovarian maturation in f emale eel, GSI increasing significantly to 38-49%. 4 implantations of MT or ADSD (50 mu g/g body weight/15 days) induced spermatogenesis and spermiation in the male eel, GSI increasing to 2.1-3.5%. MT or ADSD i mplantations significantly elevated pituitary and serum GtH contents. ADSD or MT implantations resulted in the significant elevation of seru m estradiol levels in female eel and serum testosterone levels in male eels. In female eel, ADSD implantations significantly increased mamma lean-libe-gonadotropin-releasing hormone (mGnRH) content in brain and pituitary. These results demonstrated that the positive feedback effec ts of sex steroids on the brain (hypothalamus)-pituitary-gonad axis pl ay an important role on the induction of gonadal development and matur ation in the Japanese eel, and the endogeneous GtH is the key hormone during these physiological processes. In the matured female eel, ovula tion and spawning can be induced 18-21 hours following an injection of CPE alone or in combination with [D-Ala(6), Prog-NEt]-luteinizing hor mone-releasing hormone (LHRH-A) and dopamine antagonist domperidone (D OM).