Effects of LED spectra and photoperiods on growth performance, expression of growth-and immune-related genes and intestinal flora in juvenile sea cucumber, Apostichopus japonicus

Light environments significantly influence the physiology, growth and behavior of aquatic animals. Due to the economic importance of sea cucumbers ( Apostichopus japonicus，Aj ) in aquaculture, understanding their response to various light conditions has significant practical implications. In this study, Juvenile sea cucumbers were cultured for 40 days under three photoperiods: 0 L:24D (DD), 14 L:10D (LD), and 24 L:0D (LL), with three light spectra of full-spectrum (W), orange (O) and red (R). The effects of light environments on growth performance, expression of growth- and immune-related genes, and intestinal microbiota composition in sea cucumbers were analyzed. Results exhibited that sea cucumbers in the LD group showed significantly greater growth under full-spectrum and red light. The expression of MAPK-7 and GDF-8 genes was significantly higher in the LD group across all light spectra. Notably, the c-myc and HSP90 gene exhibited significantly higher expression under red light in the LD group. Across all spectra, the LD group had significantly higher expression of HSP70 and HSP90 compared to the LL group. Aj-p105 was upregulated in the LD group under full-spectrum and red light, while Aj-p50 expression was downregulated in the LL group across all spectra . The lys gene showed significant upregulation only in the red light LD group. Analysis of gut microbiota revealed that daily LD photoperiods with red light exposure increased the abundance of beneficial bacteria, such as Verrucomicrobiota , Rhodobacteraceae and Rubritalea . Pathogenic bacteria, including Vibrio , Ralstonia and Aeromonas , were more abundant in the LL group. In summary, 14 h of daily red light exposure promoted growth, boosted immunity, helped maintain a stable and healthy gut microbiota, and potentially prevented disease in juvenile sea cucumbers.