Effect of green wavelength light on stress and appetite responses of olive flounder (Paralichthys olivaceus) following feed deprivation and re-feeding

•The fasted 1 week/fed 3 weeks with green light showed the highest values in feed efficiency.•Orexigenic gene were expressed less in green light than white light during the fasting period and more during the feeding period.•The protocol used for the fasted 1 week/fed 3 weeks was the most effective for short-term starvation and re-feeding.•Green LEDs have a beneficial effect that reduce stress by food deprivation and promote growth on cultured fish. Feeding regimes and light may influence the productivity and wellbeing of aquatic animals; however, little is known regarding any interactive effects. We investigated if short-term deprivation and refeeding regimes and green light promotes growth by reducing stress in the olive flounder, using two lights [white fluorescent bulb (white) and green-wavelength LED (green)] in 4 feeding trials (fed 4 weeks, 4F; fasted 1 week/fed 3 weeks, 1S-3F; fasted 2 weeks/fed 2 weeks, 2S-2F; fasted 4 weeks, 4S). At the end of the feeding periods, weight gain rate (WGR), daily feed intake (DFI), and cumulative food intake (CFI) of 4F green group were significantly higher than other groups (p < 0.05), and the 1S-3F green group reached the WGR and DFI of the 4F white group (p> 0.05). Also, 1S-3F green group showed the highest values in feed efficiency (FE) (p < 0.05). In addition, mRNA expressions of neuropeptide Y (NPY), melanin concentrating hormone (MCH), and insulin like growth factor (IGF-1) were significantly higher in the 1S-3F green group at 4 weeks than in the other periods (p < 0.05). Immunohistochemistry (IHC) staining of NPY in diencephalon revealed that the brown colored increased with longer fasting period under white light. These results suggested that the 1S-3F feeding regime in the short term (4 weeks) was the most effective for short-term feed deprivation and re-feeding. Furthermore, green light had an especially beneficial effect that reduced stress and promoted appetite for refeeding in cultured fish. Our findings are expected to work toward a positive aquaculture environment for animal welfare.