Daily cycles in serum gonadotropin levels in the goldfish: effects of photoperiod, temperature, and sexual condition

Abstract

The effects of temperature (12 and 21 °C) and photoperiod (16 h light, 8 h dark; 8 h light, 16 h dark) on daily cycles of serum gonadotropin (GtH) in goldfish with a regressed gonad (GSI = 1.1%), females undergoing ovarian recrudescence (GSI = 5.2%), and females with a mature gonad (GSI = 11%) were investigated. Serum GtH levels were measured by radioimmunoassay. Fish with regressed gonads either did not show significant daily fluctuations in serum GtH levels under different environmental regimes or showed daily fluctuations smaller in magnitude than those of females undergoing ovarian recrudescence or mature females. The patterns of daily variations of GtH levels under the same photoperiod and temperature regime were somewhat similar in the latter two groups. Also, under similar environmental conditions, although the GtH levels of females undergoing ovarian recrudescence and mature females were higher than the GtH levels in fish with regressed gonads most of the time during the 24-h period, during a portion of the 24-h period the GtH levels of all three groups were similar.