Effects of different green light intensities on the growth performance and endocrine properties of barfin flounder Verasper moseri

Abstract We previously reported that the somatic growth of barfin flounder, Verasper moseri , was effectively stimulated by the green light compared to the blue and red lights. Herein, we report the effects of different green light intensities on the growth and endocrine system of the fish. Fish were reared in a dark room with light from a light-emitting diode (LED) at a peak wavelength of 518 nm under controlled photoperiod (10.5:13.5 h, light:dark cycle; 06:00–16:30, light) with three levels of photon flux density (PFD)—2 (low), 7 (medium), or 21 (high) μmol·m −2 ·s −1 at the water surface. The average water temperature was 10.2 °C, and the fish were fed until satiety. The fish reared under high PFD of green light showed the highest specific growth rates, followed by the medium PFD group. Under high PFD, the fish showed the highest amount of melanin-concentrating hormone mRNA in their brains and insulin in plasma, while the lowest amount of growth hormone was observed in their pituitary glands. These results suggest that the green light stimulated the growth of barfin flounders in a light intensity-dependent manner in association with their central and peripheral endocrine systems. However, when the fish were reared in an ordinary room where they received both ambient and green LED lights, the fish under LED and ambient light grew faster than those under ambient light only (control). Moreover, no difference was observed in the specific growth rate of the fish reared under the three different green LED light intensities, suggesting that the growth was equally stimulated by the green light within a certain range of intensities under ambient light.