Abstract
This research studied the effects of glycerol monolaurate (GML) to diets on the digestive capacity, intestinal structure, intestinal microbiota, and disease resistance for juvenile pompano Trachinotus ovatus (mean weight = 14.00 ± 0.70 g). T. ovatus were, respectively, fed six diets containing 0.00, 0.05, 0.10, 0.15, 0.20, and 0.25% GML for 56 days. The highest weight gain rate was observed in the 0.15% GML group. In the intestine, amylase activities in the 0.10, 0.15, 0.20, and 0.25% GML groups were significantly increased, compared with 0.00% GML group (P < 0.05). Lipase activities in the 0.10 and 0.15% GML groups were significantly increased (P < 0.05). Similar significant elevations in the protease activities were also found in the 0.10, 0.15, and 0.20% GML groups (P < 0.05). Amylase activities were significantly higher in the 0.10, 0.15, 0.20, and 0.25% GML groups than that in the 0.00% GML group (P < 0.05). Villus lengths (VL) and muscle thicknesses (MT) of the 0.05, 0.10, 0.15, and 0.20% GML groups were significantly enhanced, and the villus widths (VW) in the 0.05, 0.10, and 0.15% groups were significantly increased (P < 0.05). Additionally, 0.15% GML significantly improved the intestinal immunity by upregulating interleukin 10 (il-10), increasing beneficial bacteria abundances (e.g., Vibrio, Pseudomonas, and Cetobacterium), downregulating nuclear factor kappa b (nf-κb) and interleukin 8 (il-8), and decreasing harmful bacteria abundances (e.g., Brevinema and Acinetobacter) (P < 0.05). After challenge test, GML significantly increased the survival rate (80%-96%) (P < 0.05). In addition, ACP and AKP activities in the GML-supplemented groups were significantly higher than those in the 0.00% GML group, and LZM activity was significantly higher in the 0.05, 0.10, 0.15, and 0.20% GML groups than that in the 0.00% GML group (P < 0.05). In summary, 0.15% GML significantly promoted the intestinal digestibility, improved the intestinal microflora, regulated intestinal immune-related genes, and increased resistance to V. parahaemolyticus of juvenile pompano T. ovatus.