Locomotor activity rhythm of catfish Heteropneustes fossilis are prominently regulated by light-dark cues

Abstract

It is interesting to explore, the circadian locomotor activity rhythm of dark adapted fishes. Therefore, it is aimed to investigate the circadian locomotor activity rhythm of catfish, Heteropneustes fossilis under different light regi-mens- light-dark condition LD 12:12, constant dark condition DD, constant light LL and dark-light condition DL 12:12 in both male and female. The study was conducted sequentially under LD 12: 12 (LON 0500 and LOFF 1700) and thereafter under the DD, LL and DL each for at least 10-12 consecutive days. The locomotor activity was monitored using Stanford Chronobiology Kit at a fixed period of 24 h. The three rhythm parameters obtained were Mesor (M, rhythm-adjusted 24-h average), amplitude (A) and acrophase (peak, Ø). All fish exhibited a statistically significant (p<0.001) circadian rhythm in locomo-tor activity under all light regimens LD, DD, LL and DL. The circadian ampli-tude was significantly declined under constant DD and LL. A significant shift was displayed in the circadian acrophase in all fish under each photic re-gimes LD, DD, LL and DL. The effect of light condition on M, A and Ø was sig-nificant, while gender imposed no effect. Chi-square periodogram revealed τ > 24 h in locomotor activity of most of the replicates under DD and LL. The respective study suggests that the endogenous circadian clocks in catfish H.fossilis are weakly expressed under constant conditions and requires light-dark LD or dark- light DL cues to generate/express the circadian rhythm in locomotor activity.