Seasonal fluctuations in gonadotropin levels in the plasma and gonads of male and female tilapia, Oreochromis mossambicus

Syferkuil Dam is situated 8 km NW of the University of the North and comprises a series of eight interconnected rectangular dams. having cement sides and mudbottoms. Throughout the experimental period, male and female adult specimens of the mouthbrooding tilapia, Oreochromis mossambicus were collected for further analysis. Aspects of the reproductive physiology of O. mossambicus that were investigated included the role of gonadotropin hormones in reproduction. There are two distinct gonadotropins in O. mossambicus, luteinizing-like hormone (LH-like), and follicle stimulating-like hormone (FSH-like). Both of these hormones are secreted in response to increased water temperature and both are involved in enhancing spawning. The gonadotropins also provide the impetus for steroid hormone secretion to occur. Human chorionic gonadotropin (HCG) plays a role in the final maturation of the oocytes within the female ovary. The results imply a close interaction between environmental cues and endocrine control of reproduction. Endocrine control cannot be sustained without the appropriate environmental cues required to stimulate reproduction.