Simple SummaryMost studies have focused on water temperature and photoperiods on the effects of growth and reproduction in fish, but the light spectrum also plays an important role in inducing the synthesis and secretion of growth-/reproduction-related hormones. In this study, the juvenile red spotted grouper was exposed to four light spectra from white, red, blue, or green light-emitting diodes (LEDs) for two months. The fish exposed to white LEDs exhibited the best growth, although the expression levels of growth hormone (GH) showed no significant differences and the pre-pro-somatostatin-I (PSS-I) expression levels significantly increased. Four LED spectra were effective in stimulating food intake as the expression levels of neuropeptide Y significantly increased. The gonadal development advanced from chromatin nucleolar-stage oocytes to perinucleolar-stage oocytes in all four LED groups, while there were no significant differences in FSHβ and LHβ expression. This result suggests that FSHβ and LHβ may not have played important roles in gonadal development when these fish were exposed to the four light spectra. Collectively, our results provide evidence that the natural light condition (white LED condition) is a better choice for the growth of juvenile red spotted grouper in captivity during summer.AbstractThe light spectrum is a key environmental cue involved in growth and reproduction in teleosts. This study investigated the effects of exposure on juvenile red spotted grouper exposed to white (control), red (590 nm), blue (480 nm), and green (520 nm) light-emitting diodes (LEDs) (12 h light:12 h dark) for two months. The body weight (BW), total length (TL), condition factor (CF), weight gain rate (WGR), gonadosomatic index (GSI), and hepatosomatic index (HSI) were assessed. Gonadal development was observed. The gene expression of growth-related hormones, such as growth hormone (GH), pre-pro-somatostatin-I (PSS-I), neuropeptide Y (NPY), and CCK, and of reproduction-related hormones, such as Kiss1, Kiss2, GPR54, sbGnRH, FSHβ, and LHβ, was analyzed. The results showed that the fish in the white LED group exhibited the best BW, TL, CF, WGR, and HSI after one or two months. The fish exposed to white LEDs showed the best growth after two months, but no significant differences in GH levels were detected. Contrarily, the expression levels of the PSS-I significantly increased (p< 0.05) in fish from the white group, suggesting the complex regulation of GH production and the limited effects of PSS-I on the inhibition of GH synthesis and somatic growth. The significantly increased NPY levels in the four LED groups (p< 0.05) indicated that these four LED spectra were effective in stimulating food intake and energy homeostasis. After two months, the gonads developed from chromatin nucleolar-stage oocytes to perinucleolar-stage oocytes in the four LED groups. The gene expression of Kiss2 and GPR54 in the four LED groups and of sbGnRH in the white and blue LED groups significantly increased when compared to that in the initial group (p< 0.05), while there were no significant differences in FSHβ and LHβ expression in the four LED groups. These results suggest that FSH and LH may not play important roles in gonadal development in juvenile red spotted grouper that are exposed to these four LED spectra.