Effects of light spectrum, intensity and photoperiod on gonadal development and immunity of Hexagrammos otakii

A 60-day trial was conducted to evaluate the effects of light spectrum, light intensity, and photoperiod on gonadal development, reproductive endocrine activity, and immune status of fat greenling ( Hexagrammos otakii ). An L9(3³) orthogonal design tested nine of the twenty-seven possible factor combinations using three light spectra (red, 629 nm; green, 533 nm; and blue, 450 nm), three photometric setpoints (200, 1500, and 3000 lx), and three photoperiods (8L:16D, 12L:12D, and 24L:0D), together with a natural-light reference. Gonadal histology and plasma immunoglobulin M (IgM), complement component 3 (C3), 17β-estradiol (E2), and testosterone (T) were assessed. Compared with the natural-light reference, blue light at 200 lx under 8L:16D and green light at 200 lx under 24L:0D were associated with higher proportions of advanced germ cells and significantly higher plasma E2 and T concentrations (P < 0.05). Several combinations involving red light or the highest tested illuminance showed lower sex-steroid concentrations and less advanced gonadal development. Plasma IgM concentrations were highest under green light at 1500 lx with 12L:12D and blue light at 200 lx with 8L:16D, whereas C3 concentrations were highest under red light at 3000 lx with 24L:0D and blue light at 3000 lx with 12L:12D. Orthogonal range analysis identified 200 lx as the most favorable tested photometric setpoint, whereas estimated photoperiod main effects differed between ovarian and testicular development. The corresponding theoretical complete combinations were not directly tested and require further validation. These responses may involve melatonin-mediated modulation of the hypothalamic-pituitary-gonadal axis, although melatonin and gonadotropins were not directly measured. The findings provide a basis for refining artificial-light management in H. otakii broodstock culture while highlighting the need for validation under directly measured and matched photon irradiance.