ABSTRACT
Diurnal changes in daylength and temperature influence circadian rhythm of melatonin synthesis in the fish pineal organ. All core clock genes and clock-controlled aanat2 gene are expressed in the pineal organ of teleosts. However, there is paucity of information on the circadian rhythm of expression of clock genes and any clock-controlled gene in the pineal organ of any tropical/subtropical fish species under natural photoperiod and temperature during different phases of the annual breeding cycle and/or seasons. Therefore, we studied circadian rhythms of expression of clock genes (clock, bmal1, per1, per2, per3, cry1 and cry2) and aanat2 in the pineal organ of the catfish, Clarias gariepinus maintained under natural environmental conditions during different phases of its annual breeding cycle. All clock genes and aanat2 gene invariably exhibited prominent circadian rhythm of expression in the fish pineal organ irrespective of seasons/breeding phases. Further, acrophase, mesor and amplitude of the circadian rhythm of expression of the clock genes and aanat2 gene responded differently to different seasons. Our findings suggest that photoperiod-, temperature- and season-independent circadian rhythm of expression of clock genes and aanat2 gene in the pineal organ enable it to act as a potential master clock in the fish under natural conditions.
Acknowledgments
The authors are thankful to Dr. Roelof A. Hut, Chronobiology Unit, Centre for Behaviour and
Neurosciences, University of Groningen, Netherlands for his help in performing Cosinor analysis of the data.
Disclosure statement
No potential conflict of interest was reported by the author(s).
Correction Statement
This article has been republished with minor changes. These changes do not impact the academic content of the article.