Effect of estrogen administration on oviposition of the fish, Oryzias latipes.

During the breeding season extending from spring to summer, the ovaries of the fish, Oryzias latipes, contain hundreds of follicles, each with an egg at various stages of maturation. Usually, five to fifty eggs are laid by a single female almost every morning(Egami, 1954c). On the other hand, ovaries are small and inactive in winter months. The present author has already reported that small winter ovaries of Oryzias females are caused to develop when fish are kept at 22-26•Ž, and that development of winter ovaries following exposure to higher temperature is inhibited by administration of large doses of estrogens(Egami, 1954b, d). In the present paper, the results of experiments designed to study the effects of estrogen administration on the ovaries of Oryzias latipes in the breeding season will be presented. The author wishes to thank Profs. Yo K. Okada and Kiyoshi Takewaki for their kind criticism and encouragement.