Annual changes in plasma levels of gonadotropin and steroid hormones in goldfish.

Abstract

Annual changes in the plasma levels of gonadotropin (GtH) and steroid hormones were studied in goldfish. Plasma GtH levels in both sexes were low during winter, and rapidly in-creased in the spawning season in spring. Although gonadosomatic indices (GSI) descresed after the spawaing period, plasma GtH continued to increase, keeping high levels during summer, and declined in autumn. Changes in the plasma levels of steroid hormones were highly correlated with those of GSL Plasma levels of estradiol-17β (E2) and testosterone in the female were low during winter, and increased rapidly in early spring prior to the GtH increase, then elevated levels were maintained during the spawning period. E2 and testosterone levels decreased after the spawning season, and testosterone showed an increase in autumn. Changes in testosterone and 11-ketotestosterone levels in male were parallel and similar to those of E2 and testosterone in female, but increases of these steroids in autumn were more prominent than those in the female. There is little correlation between plasma levels of GtH and steroid hormones, and changes in the plasma GtH levels seem to be more related to the seasonal change of the water tempera-ture.