Hormone changes during the ovulatory cycle in goldfish

Abstract

Hormone profiles during the ovulatory cycle were studied in goldfish. Blood samples were taken from female goldfish every 4 days between 1400 and 1700 hr during the course of repeated ovulations for a duration of 3 months, and plasma hormone levels of 3 days before and after ovulation were compared. Plasma gonadotropin (GtH) levels did not show significant changes except a surge for ovulation, but tended to show higher levels before the surge than those after the surge. Plasma testosterone before ovulation showed significantly higher levels compared with those after ovulation. Plasma estradiol-17β (E 2) levels remained low for 3 days prior to ovulation. Postovulation E 2 levels that were significantly higher than the preovulation levels were kept elevated and declined on the third day after ovulation. These results indicate that E 2 is mainly produced in the first part of the ovulatory cycle and testosterone in the latter part followed by the GtH surge and ovulation at the end of the cycle. This shift in steroid pattern from E 2 to testosterone seems to be similar to those observed in salmonid fishes except for the time scale. The synchrony of ovulation in goldfish is also discussed in relation to physiological and external factors which influence the occurrence of ovulation.