Synchronization of plasma sexual steroid concentrations and gonadal cycles in the sleeper, Eleotris acanthopoma

This paper describes the possible influences of environmental factors on the reproductive cycle of Eleotris acanthopoma in the Kaoping River estuary. For over 1 yr, gonad gross morphologies of the fish were examined by light microscopy, and plasma 17 beta-estradiol (E2) and testosterone (T) were analyzed by ELISA. In male E. acanthopoma, plasma T concentrations show a single seasonal cycle, with a peak in the summer (June to August) following the profile of the gonadosomatic index (GSI). In females, plasma E2 concentrations are significantly elevated during summer in accordance with the GSI. Low temperatures and a short photoperiod in the winter correlate well with the arrest of gonad maturation. Annual patterns of plasma E2 and T levels are similar to those of GSI changes existing in E. acanthopoma of either sex. These findings indicate that both temperature and photoperiod dominantly affect the reproductive cycle of E. acanthopoma.