Transcriptomic analysis of the effect of dietary melatonin on liver immunity in rice field eel (Monopterus albus)

The aim of this study was to investigate the effects of the dietary effects of melatonin, particularly in relation to its ability to regulate the immune system. A total of 360 fish were fed with different concentrations of melatonin (0, 30, 60, 120, and 240 mg/kg) for 70 days. The activities of antioxidant and immune-related enzymes in the liver showed that at a concentration of 120 mg/kg, the activities of superoxide dismutase, catalase, glutathione peroxidase, lysozyme, and alkaline phosphatase were significantly increased, while the content of malondialdehyde and the activities of alanine aminotransferase and aspartate aminotransferase were decreased (p < 0.05). In addition, the expression of HSP-90, ZO-1, IL-10, and TGF-β were increased, and the expression of NF-kB, IL-1β, IL-8, and TNF were decreased. The liver tissues from control group and 120 mg/kg melatonin group were subjected to transcriptome sequencing for further analysis. Transcriptomic analysis identified 1160 DEGs (577 up-regulated genes and 583 down-regulated genes). The most significant KEGG-enriched signaling pathways of these DEGs were motor proteins, ECM-receptor interaction, PPAR signaling pathway, DNA replication, and linoleic acid metabolism. In summary, dietary melatonin improved the growth performance rice field eel, enhanced the antioxidant and immune status of the liver, which can provide a reference for future research on nutritional supplementation and melatonin efficacy of rice field eel.