Chronic effects of light irradiated from LED on the growth performance and endocrine properties of barfin flounder Verasper moseri

We investigated the effects of specific wavelengths of light on the growth of barfin flounder. The fish, reared in white tanks in a dark room, were irradiated with light from light-emitting diodes (LEDs) with peak wavelengths of 464 nm (blue), 518 nm (green), and 635 nm (red) under a controlled photoperiod (10.5:13.5, light-dark cycle; 06:00-16:30, light). Fish were reared for four weeks in three independent experiments at three different water temperatures (averages of 14.9 °C, 8.6 °C, and 6.6 °C). The fish irradiated with blue and green light had higher specific growth rates (% body weight⋅day−1) than fish irradiated with red light. Notably, green light had the greatest effect on growth among the three light wavelengths at 6.6 °C. In the brains of fish reared at 6.6 °C, the amounts of melanin-concentrating hormone 1 mRNA under green light were lower than those under red light, and amounts of proopiomelanocortin-C mRNA under blue and green light were higher than those under red light. No differences were observed for other neuropeptides tested. In the pituitary, no difference was observed in growth hormone mRNA content. In plasma, higher levels of insulin and insulin-like growth factor-I were observed in fish under green light than those of fish under red light. These results suggest that the endocrine systems of barfin flounder are modulated by a specific wavelength of light that stimulates somatic growth.