Surfacing activity rhythm in Clarias batrachus: effect of different phases of annual reproductive cycle

Abstract

The surfacing activity rhythm in Clarias batrachus during different phases (preparatory, spawning, post-spawning and resting) of its annual reproductive cycle was examined. Live Clarias batrachus of mixed sex were procured from the local market during the respective phases and kept in stock aquaria under laboratory conditions for proper acclimation. Following acclimation, the individuals were randomly selected from the stock aquaria and kept in the specially designed glass aquaria inside the chronocubicles for recording of the surfacing activity. The animals were exposed under a LD 12:12 regime (lights on at 06:00) during each phase of the annual reproductive cycle. The surfacing activity was recorded with the help of infrared photoswitches and a microprocessor based event recorder. During all the studied phases of the annual reproductive cycle under standard LD 12:12, most of the individuals exhibited a statistically significant circadian rhythm with a prominent 24 h period in their surfacing activity. In addition, statistically significant rhythms with τ = 12 h and 6 h have also been noticed in most of the individuals during all the studied phases. It appears from actograms that the activity rhythm is entrained with the timings of light on/off, irrespective of phases of the annual reproductive cycle. The activity elevation started synchronously with the onset of dark and declined as the lights came on. Acrophases of the activity also occurred during the dark phase of the light–dark cycle. The daily mean of the surfacing activity was found to be elevated during the spawning phase compared to the other phases of the annual reproductive cycle and the lowest level of daily mean activity was noticed during the resting phase.