Dietary Enterococcus faecalis SZ07 Improves Intestinal Health, Immune Function and Gut Microbiota Homeostasis in Golden Pompano (Trachinotus ovatus)

Trachinotus ovatus (golden pompano) represents one of the dominant high-value mariculture fish species farmed across coastal regions of China. In intensive farming modes, intestinal damage and immune suppression are frequent issues in golden pompano; the widespread application of antibiotics in disease control has also triggered increasing worries about ecological risks and aquatic product safety. Host-origin probiotics have been widely recognized as a green and safe strategy to mitigate health risks and promote growth in farmed fish. Nevertheless, the regulatory roles and mechanisms of autochthonous E. faecalis strains on the intestinal health of golden pompano are still poorly understood. In this study, a 42-day feeding trial was conducted using golden pompano reared in a large-capacity floating net-cage system. The experimental fish were fed diets supplemented with different concentrations of E. faecalis SZ07 (1 × 105 to 1 × 109 CFU/g feed). Dietary supplementation with SZ07 at suitable doses (1 × 107 to 1 × 108 CFU/g feed) notably improved intestinal tissue structure, elevated the activities of digestive, antioxidant, and immune enzymes, and modulated the mRNA levels of key immune genes in the spleen. Analysis of the gut microbiota revealed that dietary E. faecalis SZ07 reshaped the intestinal microbial community, with an increased abundance of beneficial taxa and a decreased proportion of opportunistic pathogens. Taken together, our results indicate that autochthonous E. faecalis SZ07 acts as an effective probiotic to enhance intestinal health and immune function of golden pompano and offers technical support for the healthy development of its aquaculture industry.