Glycerol monolaurate enhances growth performance, lipid metabolism, and inflammatory response in common carp fed high lipid diets

A feeding trial was conducted to investigate the effects of glycerol monolaurate (GML) on growth performance, lipid metabolism, inflammation, and related gene expression in common carp fed a high lipid diet. Juvenile common carp were distributed into 18 cages and fed one of six isonitrogenous diets: a normal lipid diet (control diet, CT), a high lipid diet (HL), and high lipid diets supplemented with 0.5, 1, 2, and 4 g kg⁻¹ GML (designated as GML-0.5, GML-1, GML-2, and GML-4, respectively), with three replicates per treatment. After 56 days of feeding, the results indicated that the final body weight (FBW) and specific growth rate (SGR) in the GML-1 and GML-2 groups were significantly higher than those observed in the CT, HL, and GML-4 groups (P < 0.05). The crude lipid content in the hepatopancreas of the GML-1 and GML-2 groups was significantly lower than that in the HL group (P < 0.05). Morphological analysis of the hepatopancreas revealed a reduction in vacuole presence with GML supplementation (P < 0.05). Additionally, GML supplementation significantly enhanced the development of intestinal structures of common carp. The inclusion of GML significantly influenced the quality of the fillet, as evidenced by notable increases in hardness, gumminess, chewiness, and shear force compared to the HL group (P < 0.05). Additionally, the dripping loss of raw fillets in the GML groups decreased than that observed in the HL group (P < 0.05). Furthermore, GML-1 and GML-2 groups exhibiting the lowest serum TG levels among all groups (P < 0.05). Conversely, serum high density lipoprotein cholesterol (HDL) levels significantly increased with GML supplementation, with the GML-2 group demonstrating the highest HDL content (P < 0.05). Key genes of lipid synthesis in the hepatopancreas were down-regulated, whereas genes involved in lipolysis were up-regulated in the GML-1 and GML-2 groups relative to the HL group (P < 0.05). KEGG functional annotation analysis of differentially expressed genes in the hepatopancreas of fish fed GML-supplemented diets revealed significant alterations in the PPAR signaling pathway. GML effectively enhanced the antioxidant enzyme activities of hepatopancreas, intestine, spleen, kidney, and serum following high lipid feeding accompanied with the significant up-regulation of antioxidant genes in the hepatopancreas and intestine of the GML-1 and GML-2 groups. Simultaneously, pro-inflammatory factors in these tissues were significantly down-regulated, while anti-inflammatory factors were markedly up-regulated in the GML-1 and GML-2 groups compared to the HL group (P < 0.05). In summary, common carp fed high lipid diets supplemented with 1–2 g kg⁻¹ GML exhibited improved growth performance, enhanced fillet quality, regulated lipid metabolism, promoted intestinal structural development, and bolstered both antioxidant and immune capacities.