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  • Title: Light intensity and suppression of nocturnal plasma melatonin in Arctic charr (Salvelinus alpinus).
    Author: Liu Q, Manning AJ, Duston J.
    Journal: Comp Biochem Physiol A Mol Integr Physiol; 2019 Feb; 228():103-106. PubMed ID: 30471350.
    Abstract:
    The problem of early sexual maturation among farmed Arctic charr and other salmonids can be effectively reduced by 24 h light overwinter, provided it is bright enough to over-ride interference from the natural daylength cycle. To determine the threshold light intensity to suppress the nocturnal elevation of plasma melatonin, three groups of individually tagged fish (n = 26-28/group ca. 1040 g) were reared on 12 h light: 12 h dark (LD 12:12) and subjected to nighttime light intensities of either 50-65, 0.1-0.3 or 0 (control) lux for five months (November to April). Daytime light intensity was 720-750 lx. Diel plasma melatonin profiles in both November and April were similar; mean daytime levels ranged from 20 to 100 pg/ml, and nighttime levels were inversely proportional to light intensity. In the control group at 0 lx, plasma melatonin increased about four-fold after lights-off, ranging between 320 and 430 pg/ml. Nighttime light intensity of 0.1-0.3 lx halved plasma melatonin levels to 140-220 pg/ml, and 50-65 lx further reduced the levels to one quarter of the control group, 68-108 pg/ml. Among the lit groups, daytime plasma melatonin levels were about 20-30 pg/ml, significantly lower than the nocturnal levels suggesting the diel hormonal rhythm was not completely abolished. Fish grew steadily from about 1100 g to 1600 g between November and April, independent of light intensity (P = .67). Overall, the study demonstrated the sensitivity of pineal melatonin hormone to different light intensities in Arctic charr.
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