Locomotor activity rhythm in catfish Heteropneustes fossilis as a function of shoal size under different light regimens

ABSTRACT

The information on the circadian characteristics of catfish in shoals is scanty. We examined the circadian locomotor activity rhythm of catfish Heteropneustes fossilis either singly housed (SS1) or in shoals of four (SS4) and six (SS6) under different light regimens. We carried out the study sequentially under LD₁ (12:12), constant darkness (DD), LD₂, continuous light (LL), LD₃, and DL (12:12). Each condition was for at least 10–12 consecutive days. We analyzed the time-series data by employing Cosinor rhythmometry to detect circadian rhythm characteristics in locomotor activity at a fixed time window with a τ = 24 h. Results indicated that singly housed or shoals exhibited statistically significant (p < .001) circadian rhythm in locomotor activity under LD conditions with a higher activity level during the dark phase. Further, we observed free-running rhythms in locomotor activity under DD and LL, irrespective of the shoal sizes. In phase inverse DL, both singly housed and shoals demonstrated higher activity in the dark phase. The two-way ANOVA results revealed a significant effect of the factor ‘light regimen’ on amplitude and acrophase; the factor ‘shoal size’ produced a statistically significant impact on the mesor only. Both shoals showed significantly higher mesor than singly housed fish. The circadian amplitude declined under constant conditions of DD and LL. The locomotor activity rhythm exhibited a free-running pattern with a τ_FR greater than 24 h under both DD and LL conditions. We conclude that light is a more prominent factor for the entrainment of circadian activity in catfish H. fossilis. However, the extent of social aggregation (shoal size) has little or no effects on the characteristics of circadian locomotor activity rhythm in H. fossilis.

KEYWORDS:

• Locomotor activity rhythm
• light regimen
• shoal size
• free-running period
• Heteropneustes fossilis

Acknowledgements

This work is a part of the Doctor of Philosophy thesis of one of the authors (PK). The authors wish to thank the Head of the Department, School of Studies in Life Science, Pandit Ravishankar Shukla University, Raipur, for providing animal laboratory facilities. We are also obliged to anonymous reviewer for offering us valuable suggestions for the improvement of the manuscript.

Disclosure statement

The authors report no conflicts of interest.

Additional information

Funding

The work was supported by the Department of Science and Technology (DST), Ministry of Science and Technology, New Delhi, India, in the form of an award of Inspire Fellowship to one of us (PK) [IF 110519 Dy.No.100 /IFD /8622/ 2011-2012]. This work also received support from University Grants Commission, New Delhi, under the scheme UGC-DRS-SAP (Phase-III) sanctioned to the SoS in Life Science, Pandit Ravishankar Shukla University, Raipur in the thrust area - Chronobiology [Grant No. F-3-2/2016/DRS-III (SAP-II)].