Effect of LED light spectra on circadian rhythms in goldfish Carassius auratus: expression profiles following thermal stress

We investigated the effects of light spectra on circadian rhythms under high thermal stress using red, green and purple light-emitting diodes (LEDs). To assess differences in circadian rhythms during high thermal stress under different LED light spectra, we measured changes in the expression of the melatonin receptor 1 (MT1), period 2 (Per2), and cryptochrome 1 (Cry1) genes and MT1 protein, and in the plasma melatonin and glucose levels. Under high water temperatures and red light conditions, MT1 expression and plasma melatonin and glucose were significantly higher than under low water temperatures and other light spectra, but Per2 and Cry1 expressions were significantly lower. Thus, high water temperatures induce oxidative stress and melatonin acts as an antioxidant molecule. Further, melatonin regulates circadian rhythms via clock genes, and green and purple lights may be suitable for maintaining circadian rhythms in goldfish Carassius auratus, as these wavelengths generally penetrate freshwater more efficiently than does red light.