STUDIES ON THE BREEDING BIOLOGY OF THE EEL (ANGUILLA JAPONICA TEMMINCK SCHLEGEL) Ⅳ. THE GONADOTROPIN SECRETION, GONADAL DEVELOPMENT AND ULTRASTRUCTURE OF GONADOTROPIC CELL OF THE EEL DURING PROCESS OF INDUCED MATURATION.

Estradiol stimulates hormonal synthesis of GtH cells through a positive feedback, leading to a significant increase in pituitary GtH content. Joint treatments with LHRH-A and reserpine result in a significant increase in serum GtH level after a pretreatment with estradiol. Joint treatments with carp pituitary homogenate, HCGand LHRH-A (des-Gly10-D-Ala6-LHRH-ethylamide) yield a better result on induced sexual maturation both in male and female eel than merely using carp pituitary homogenate or HCG. It indicates that both exogenous and endogenous gonadotropin are essential to the induction of sexual maturation of this fish. In mature eel, hypertrophied GtH cells, distinct degranulation and marked dilatation of cisternae of the rough endoplasmic reticulum, suggest the release of hormone from the GtH cells.