FFECTS OF EXOGENOUS HORMONES ON SERUM STEROID HORMONE IN FEMALE RICEFIELD EEL (MONOPTERVS ALBUS)
TAO YA-XIONG LIN HAO-RAN(Department of Biology, Zhongshan University, Guangzhou 510275)
The effects of salmon gonadotropin-releasing hormone analogue (sGnRH-A)and/or dopamine antagonist domperidone (DOM), or exogenous gonadotropins (carp pituitary ho-mogenate, CPH and human chorionic gonadotropin, hCG) on serum steroid level of female ricefield eel at different reproductive periods were investigated. In prespawning period, serum estradiol- 17β(E2) level increased significantly at 6 hrs after injection of sGnRH-A (0.1 ug/g body weight), but the increase was not obvious at 24 or 48 hrs. In spawning period, those with higher gonosomatic indice (GSI) were more responsive than those with lower GSI. Serum E2 increased significantly at 24, but not at 6 or 48 hrs in postspawning period. DOM decreased serum steroid levels. Both CPH and hCG increased serum steroid levels at all three periods.These results indicated that gonadotropin (GTH) secretion in female ricefield eel was stimulated by gonadotropin-releasing hormone, while that whether dopamine acted as GTH releasing inhibitory factor was not clear. There were seasonal differences in response to exogenous hormones in pituitary-gonad axis, with spawning period being the most responsive. The response was quicker in prespawning than in postspawning period.