Season-dependent effect of thermopulse on gonadal recrudescence in the female catfish, Clarias batrachus.

In the present study, the female Clarias batrachus, held under long photoperiod (13L:11D), were exposed to high water temperature either constantly (24 h) and/or in form of thermopulse of 6 h and 12 h durations, separately, at different times of the day/night cycle for six weeks during the early post-spawning and late post-spawning phases of its reproductive cycle. The effects of high water temperature (30 +/- 1 degrees C) on gonadosomatic index (GSI), plasma levels of testosterone (T) and oestradiol-17beta (E2) were observed. During the late post-spawning phase, thermopulse of 12 h duration given in the morning hour increased all the studied parameters most effectively as compared to that given at evening hour of the day/night cycle or even in comparison to the fish exposed to constant high temperature.