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Meagre’s melatonin profiles under captivity: circadian rhythmicity and light sensitiveness


The present study reveals the first characterization of the plasma melatonin rhythms of the meagre (Argyrosomus regius) under aquaculture conditions. Melatonin levels were monitored during a 24 h cycle under a photoperiod of 16 L:8D and under constant darkness (DD), respectively to characterize the daily rhythm of this indoleamine and to test its endogenous origin. Besides, to identify which light intensities are perceived as night or day by this species, the degree of inhibition of nocturnal melatonin production caused by increasing intensities of light was tested (3.3, 5.3, 10.5, and 120 μW/cm2), applying 1 h light pulses at Mid-Dark. The result for melatonin daily rhythm in plasma showed a typical profile: concentration remained low during all daytime points, increasing greatly during dark points, with maximum values at 16:00 and 22:00 h, zeitgeber time. Under DD conditions, the plasma melatonin profile persisted, with a similar acrophase but with a lower amplitude between subjective day and night periods, indicating this rhythm as being endogenously driven. Moreover, meagre seemed to be very sensitive to dim levels of illumination during the night, since an intensity of just 3.3 μW/cm2 inhibited melatonin production. However, only the pulse of 5.3 μW/cm2 caused a melatonin drop till daytime concentrations. Thus, the threshold of light detection by the pineal organ was suggested as being located between 3.3 and 5.3 μW/cm2. Such results are an added value for this species biology knowledge, and in consequence to its adaptation to aquaculture conditions, allowing the improvement of culture husbandry protocols.

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This research has been financed by Projects AQUACOR (PROMAR 31-03-05FEP-003) and Prospawn (Seventh Framework Programme for Research and Technological Development, FP7/SME/2008/1), and CO is conceded an FCT grant (Fundação para a Ciência e Tecnologia, SFRH/BPD/63933/2009). Authors would also like to thank Marisa Barata for her help during fish maintenance.

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Correspondence to Catarina C. V. Oliveira.

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The authors declare that they have no conflict of interest.

Research involving animals

As stated in material and methods section, experiments were performed before the entry into force of Directive 2010/63/EU (EU 2010) as national legislation in Portugal. Nonetheless, no harmful procedures were applied to live animals and fish were reared according to the best practice. Whenever necessary, experimental procedures were performed under anesthesia and every effort was made to minimize suffering at all stages.

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Oliveira, C.C.V., Figueiredo, F., Soares, F. et al. Meagre’s melatonin profiles under captivity: circadian rhythmicity and light sensitiveness. Fish Physiol Biochem 44, 885–893 (2018).

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