A rise in rearing temperature stimulated gonadotropic hormone (c-GTH) secretion in Carassius auratus . This plasma c-GTH increase was not followed by gonadal development. No matter what the season, a rise of water temperature temporarily blocked gonadal development; however, high temperature inhibition of gametogenesis was reversible because after 9 months at 30 C, the fish showed completely and apparently normal gametogenesis. Photoperiod did not influence pituitary secretion and the mean plasma c-GTH level. However, the existence of circadian plasma c-GTH cycles indicated that photoperiod might affect gonadotropic secretion. Long winter photoperiods also strongly stimulated oogenesis. Reduced food intake for 3 months did not cause gonadotropic secretion to decrease with any of the photoperiod or temperatures used. On the other hand, at 20 C with long and short-day regimes there was a significant increase (P<0.05) of pituitary GTH in females not fed the granules. Depriving the fish of granules for 3 months caused the testes to regress at 12 C/short days and at 20 C /long days, but rehabilitation ad libitum after 1 month of fsting prevented this testicular regression.