Optimal Dietary Glycerol Monolaurate Supplementation Enhances Growth Performance and Intestinal Health in Hybrid Grouper (♀ Epinephelus fuscoguttatus × ♂ E. lanceolatus)

Abstract

This study investigated the effects of glycerol monolaurate (GML) on the growth performance, physiological efficacy, intestinal structure, and microbiota of hybrid juvenile ♀ Epinephelus fuscoguttatus × ♂ E. lanceolatus. A total of 594 groupers were administered diets supplemented with 0, 2, 4, 6, 8, or 10 g/kg of GML over an 80-day period. The findings indicated that the group receiving 4 g/kg GML supplementation demonstrated significantly enhanced growth performance, as evidenced by increased weight gain, specific growth rate, and a reduced feed conversion ratio compared with the control and other experimental groups. This growth enhancement was associated with elevated catalase and glutathione levels, suggesting improved antioxidant capacity that may contribute to enhanced immune function. Furthermore, fish in the 4 g/kg group exhibited increased digestive enzyme activity and significantly improved intestinal morphology, characterized by thicker muscular layers and a greater fold width and height. Furthermore, compared with the control group, GML supplementation elevated the relative abundance of Proteobacteria while reducing that of Firmicutes at the phylum level. At the genus level, GML markedly suppressed the relative abundance of Mycoplasma and Vibrio. These compositional alterations are potentially linked to improved energy acquisition and a decreased risk of pathogenic infections. Collectively, these results reveal that GML acts as a promising functional feed additive to boost growth performance, optimize digestive capacity, and sustain intestinal structural integrity in hybrid grouper. Based on these results, the optimal GML supplementation dose was determined to be 4 g/kg, providing valuable insights into the role of GML in aquaculture practices for hybrid grouper.

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