The Involvement of Melatonin in the Dimorphism of Glucose and Lipid Metabolism of Tilapia

In tilapia, males grow faster than females, but the metabolites/pathways behind this sexual dimorphism remain unclear. In this study, we first examined growth, feeding, serum biochemical parameters, and mRNA expression in tilapia under mono-sex and mixed-sex cultures. Tilapia raised mono-sexually grow faster than those raised in mixed-sex environments. We conducted a combined analysis of the gas chromatography–mass spectrometry (GC-MS)-based metabolome and digital gene expression (DGE) profile in the livers of immature and mature tilapia, with special reference to the sexual differences. The glucose and lipid metabolism pathways exhibited significant sexual dimorphism. The concentrations of melatonin, oxoadipate, and glucuronic acid in the tryptophan metabolism pathway showed sexual differences. Melatonin implantation inhibited food intake and growth in tilapia and impacted their glucose and lipid metabolism. After melatonin implantation, the glucose tolerance of tilapia improved, especially in females. This study generates comprehensive data elucidating the mechanisms underlying sexual dimorphism in glucose and lipid metabolism and establishes a reliable scientific basis for investigating the role of melatonin in the sexual dimorphism of tilapia.