Influences of ferulic acid on intestinal digestive and antioxidant enzymes, immune, antioxidant gene and tight junction protein expression and microbiota in hybrid grouper (Epinephelus fuscoguttatus♀ x Epinephelus polyphekadion♂)

The current study was performed to assess the effects of dietary administration of ferulic acid (FA) on digestive enzyme activities, antioxidant capacity, morphology, immunity, and microbiota in the gut of hybrid grouper (Epinephelus fuscoguttatus female x Epinephelus polyphekadion male). A total of 630 fish (9.51 +/- 0.01 g) were allocated randomly to seven dietary treatments, each with three replicates. Experiment diets supplemented with FA at the levels of 0, 40, 80, 160, 320, 640, and 1280 mg kg(-1) (FA0 (control), FA40, FA80, FA160, FA320, FA640, and FA1280), were fed to fish for 70 days. The results showed that dietary 80-160 mg kg(-1) FA intake considerably augmented the enzymes activities of digestion (lipase, trypsin, amylase, and pepsin) and antioxidation (superoxide dismutase, glutathione peroxidase, and catalase) and the values of immune parameters (Immunoglobulin, C3 and lysozyme), as well as reduced malondialdehyde content, with respect to the control group (P < 0.05). Furthermore, a significant increase in the intestinal fold height, fold width, and muscular thickness was detected in fish fed the diets containing 80-160 mg kg(-1) FA (P < 0.05). For gut genes expression, dietary supplementation of 80-160 mg kg(-1) FA significantly upregulated the transcriptional levels of the immune-related genes (interleukin 1 beta, interleukin 8, tumor necrosis factor-alpha, interleukin 10, and transforming growth factor-beta 1), the antioxidation-associated genes (superoxide dismutase, copper/zinc superoxide dismutase, and nuclear factor erythroid 2-related factor 2-like 2), and tight junction proteins genes (zonula occludens 1, Occludin, and Claudin3), whereas downregulated kelch like ECH associated protein 1 (P < 0.05). Regarding the intestinal microbiota, the FA-supplemented diets with 80 and 1280 mg kg(-1) significantly increased the alpha diversity indexes (Simpson and Shannon) and the relative abundances of Firmicutes and Bacteroidetes, as well as lowered the relative abundance of Proteobacteria (P < 0.05). Additionally, the ratio of Firmicutes to Bacteroidetes was remarkably reduced, following the diet supplemented with 80 mg kg(-1) FA, which also exhibited the decreased relative abundance of Acinetobacter and the increased relative abundances of Lactobacillus and Bifidobacterium (P < 0.05). Taken together, these results signified that the appropriate FA inclusion in diets could serve as a nutritional strategy to improve the intestinal health of hybrid grouper.