<p>Light manipulation in aquaculture offers potential for optimizing both growth and reproduction, yet the specific effects of monochromatic light in commercial-scale settings remain poorly understood. This study investigated the impact of 500-nm light-emitting diode (LED) light (13L:11D) on female olive flounders in a commercial-scale aquaculture setting over one year. Fish exposed to 500-nm light showed significantly higher body weights and condition factors compared to those under natural light. Growth enhancement was accompanied by elevated transcript levels of insulin-like growth factor-1 gene (<i>Igf-1</i>) in liver from October to February and increased hypothalamic melanin-concentrating hormone gene (<i>MCH</i>) expression from December to April. The treatment group exhibited suppressed reproductive development, evidenced by significantly lower gonado somatic index (GSI) values from October to February and delayed ovarian maturation. Histological analysis revealed that while the control group ovaries contained late vitellogenic oocytes in February, the 500-nm group maintained early vitellogenic stages. This reproductive delay corresponded with reduced expression of follicle-stimulating hormone β (<i>fshβ</i>) and luteinizing hormone β subunit (<i>lhβ</i>) genes in the pituitary gland and decreased ovarian cytochrome P450 family 19 subfamily A gene (<i>cyp19a</i>) levels during both spawning and non-spawning seasons. Notably, aralkylamine N-acetyltransferase (<i>aanat1</i>) transcript levels were significantly elevated in October and December under 500-nm light, suggesting altered melatonin-mediated regulation of physiological rhythms. These findings demonstrate that 500-nm LED lighting with 13L:11D photoperiod effectively enhances growth while suppressing reproductive development in commercial-scale olive flounder aquaculture, offering a practical alternative to traditional methods like triploid induction for managing the growth-reproduction trade-off in female olive flounders.</p>