The dietary supplementation with probiotic Bacillus cereus G1-11 improved the growth parameters, immune performances, intestinal histomorphology, and disease resistance of hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂)

Groupers are popular in the Asia-Pacific region for their high protein content, but disease remains a major challenge in their culture. Probiotics represent a safer and eco-friendly alternative to antibiotics. Although various indigenous probiotics have been studied, research specifically targeting grouper remains limited and requires further exploration. Therefore, the aim of this study was to investigate the effects of a probiotic, Bacillus cereus G1–11, isolated from the gut of hybrid grouper (Epinephelus fuscoguttatus ♀ × Epinephelus lanceolatus ♂), on multiple physiological aspects, including growth performance, expression of growth- and immune-related genes, antioxidant capacity, intestinal histology, and resistance to Vibrio harveyi. A total of 360 hybrid groupers were randomly allocated into four groups, each with three replicates of 30 fish (29.55 ± 0.10 g initial weight per fish). Fish were fed the following diets for 60 days: commercial feed without B. cereus G1–11 (group C), commercial feed containing 10⁶ CFU/g B. cereus G1–11 (group L), commercial feed containing 10⁸ CFU/g B. cereus G1–11 (group M), and commercial feed containing 10¹⁰ CFU/g B. cereus G1–11 (group H). The results showed that dietary B. cereus G1–11 improved the growth performance and up-regulated the expression of ghr1, igf-2, s6k1, and tor in the liver and muscle, as well as appetite-regulating genes in the brain of hybrid groupers, and the group H exhibited the most significant effect (P < 0.05). Meanwhile, dietary B. cereus G1–11 also elevated expression of various immune-related genes (myd88, Cu/Zn-sod, tlr3, and tnf-2) in the spleen, liver, and head kidney (P < 0.05), but increased malondialdehyde content and reduced acid phosphatase activity in the serum and liver (P < 0.05). Challenge with Vibrio harveyi indicated that myD88 is a core immune gene mediating the effects of B. cereus G1–11, potentially activating the NF-κB pathway and thereby up-regulating pro-inflammatory genes (il-1β, il-8, tnf-α) to enhance resistance, slow down death, and reduce mortality of hybrid grouper. In addition, groups L and H modulated the expression of anti-inflammatory genes (nrf-2, piscidin, tgf-β1), thereby mitigating excessive inflammatory responses. Histological analysis further revealed that B. cereus G1–11 dietary increased villus width, villus height, and microvillus height in the intestine, which may facilitate improved nutrient absorption. In conclusion, this study provides new evidence supporting the application of B. cereus G1–11 in grouper aquaculture and suggests an optimal dosage of 10¹⁰ CFU/g feed.