Effect of LED spectrum on the regulation of appetite-related hormones in the digestive tract of red seabream (Pagrus major)

Light is an external factor that stimulates the neuroendocrine system through the hypothalamus and controls hormonal regulation in fish. Specifically, various light wavelength can influence feeding behavior and feed digestion by regulating the expression of key hormones that control appetite and digestive functions or processes. In this study, we compared how the hormone-producing endocrine cells, known to be important during feed regulation and feeding, reacted in response to different light emitting diode (LED) spectrum stimulation in red seabream (Pagrus major). Fish were subjected to different light treatments (replicated thrice), namely; red (660 nm), green (518 nm), blue (450 nm), and white (full spectrum), at a 12L:12D photoperiod in a cylindrical tank equipped with LED covers. After 12 weeks of light exposure, gastrointestinal tract samples were subjected to fluorescence in situ hybridization (FISH), and immunohistochemistry (IHC) analysis to check the expression level of ghrelin (GHRL), neuropeptide Y (NPY), pancreatic polypeptide (PP), and cholecystokinin (CCK), and H&E and alcian blue-periodic acid-schiff (AB-PAS) staining to check structural influence. The results showed that the blue group exhibited the fastest body growth, followed by green, white, and red (p < 0.05). FISH analysis showed a similar pattern for GHRL expressed in the stomach and NPY expressed in both the stomach and intestine. IHC analysis revealed that PP was strongly expressed in the red and white groups, while weakly expressed in the green and blue groups. There were no visible differences in the CCK signals among the experimental groups. Moreover, H-E staining results showed no discernable morphological differences in the muscle layer and villi length of the intestine (p > 0.05), but AB-PAS staining results revealed that the number of goblet cells was the least in the red group (p < 0.05). These results illustrated that the blue group exhibited fast growth due to increase feeding strategy controlled by gastrointestinal hormones whereas, least growth and reduction was observed in red group. Based on these findings, the potential use of blue wavelength light in red seabream aquaculture is emphasized.