Melatonin Bio-Synthesizing Machinery in Fish: A Current Knowledge with a Special Emphasis on Tropical Carp

Melatonin is a chronobiotic molecule, mainly synthesized in the pineal organ in all vertebrates. Recent studies emphasize the production of this indole amine hormone in extra-pineal sources in fish as well as in other vertebrates. The present communication is aimed to put a light on the recent development on the extra-pineal sources of melatonin with special attention on the tropical carp. The importance and involvement of clock-associated genes are also taken into the consideration for understanding the integrate phenomenon of rhythm physiology. The uniqueness of the melatonin bio-synthesizing enzyme genes in fish has also been focused. The sudden changes in the environmental factors are affecting the daily and seasonal physiological activities of fish. Studies from our group on tropical carp Catla catla indicate the changes on the rhythmic pattern of these enzymes at their mRNA level. Moreover, results also focused to establish this tropical carp as a model for the studies on the rhythm biology.