Host gut-derived probiotics supplementation improves growth performance, serum and liver immunity, gut health, and resistive capacity against infection in hybrid grouper ( × ♂).

Several reports have revealed the vital role that probiotics play in fish growth and health. However, few works are available for host gut-derived probiotics on the growth, immunity, and gut microbiota of fish, especially in hybrid grouper (♀ × ♂) due to their isolation difficulty and functional verification. This study aimed at assessing 3 host gut-derived species' effects on the growth, immune and antioxidant-biochemical responses, haematological parameters, intestinal morphology, immune-related gene expression, gut microbiota, and disease resistance against in hybrid grouper. A total of 480 hybrid grouper (initial weight = 9.03 ± 0.02 g) were randomly allotted into 4 groups, namely, the group fed a basal diet without probiotic inclusion (control, B0), the group fed the basal diet with GPSAK4 (BV), the group fed the basal diet with GPSAK9 (BS), and the group fed the basal diet with GPSAK2 (BT) strains at 1.0 × 10 CFU/g. After a 6-week feeding trial, the results revealed significant improvements ( < 0.05) in the growth performance, whole fish-body proximate composition, blood haematological parameters, serum, liver, and intestinal biochemical indexes, intestinal morphology, and protection against . pathogen in the probiotic-treated groups compared with the untreated. Additionally, the expressions of intestinal tight junction genes (occludin and ), pro- and anti-inflammatory genes, including , , , , , , and , were upregulated ( < 0.05) after species administration. Host gut-derived supplementation shaped the gut microbiota by significantly increasing ( < 0.05) the relative abundance of Proteobacteria, Bacteroidetes, Actinobacteria (except the BS group), Acidobacteria (except the BT group), Cyanobacteria (except the BV and BT groups), and Verrucomicrobia phyla, as well as known beneficial genera (, , , 1 and 13, , and ), but significantly decreased ( < 0.05) the abundance of Firmicutes, Chloroflexi, and Fusobacteria phyla, and purported pathogenic genera ( and ) compared with the control group. Collectively, the results suggest that . GPSAK4, . GPSAK9 (especially this strain), . GPSAK2 dietary supplementation at 1.0 × 10 CFU/g has positive effects on the intestinal health of hybrid grouper via microbial composition modulation, thus enhancing the assimilation and absorption of nutrients to boost fish growth, immunity, and disease resistance.