Effect of dietary histamine on intestinal flora and immune response in hybrid grouper (Epinephelus fuscoguttatus♀× E. lanceolatus♂)

Since grouper feed is relatively rich in fish meal, it is susceptible to excessive histamine accumulation. In order to examine the effects of histamine on intestinal inflammation, apoptosis, non-specific immunity, and intestinal microbiota in hybrid grouper, seven isoproteic (50 %) and isolipidic (11 %) diets were created with histamine concentrations of 0, 30, 60, 120, 240, 480, and 960 mg/kg (actual levels: 72.33, 99.56, 138.60, 225.35, 404.12, 662.12, and 1245.38 mg/kg). After 8 weeks of cultivation, the levels of intestinal and serum complements 3 and 4, as well as lysozyme and alkaline phosphatase activities, gradually declined as the amount of dietary histamine increased. Furthermore, the intestinal inflammation factors (including NF-κB-inducing kinase, nuclear factor-κB inhibitor kinase, phosphatidylinositol 3-kinase, protein kinase B, interleukin-1 receptor associated kinase, ubiquitin-ligase enzyme, extracellular signal-regulated kinase, p38 mitogen-activated protein kinase, c-Jun N-terminal protein kinase, and tumor necrosis factor α) also gradually increased. Additionally, as dietary histamine level increased, the intestinal microbiota in the 225.35 and 1245.38 mg/kg histamine groups exhibited a significant reduction in both diversity and abundance compared to the control group. At the genus level, these groups showed a significant increase in the pathogenic bacteria Ralstonia , Pseudomonas , and Prauserella , along with a marked decrease in the probiotic bacterium Cetobacterium . In conclusion, a dietary histamine level exceeding 404.12 mg/kg resulted in a reduction of intestinal immunocompetence, while levels exceeding 662.12 mg/kg led to an increase in the intestinal inflammatory response. Therefore, the histamine content in hybrid grouper feed should not exceed 404 mg/kg. • The elevated histamine content in diet resulted in a reduction of non-specific immunity in intestine and activated the NF-κB signaling pathway, potentially leading to intestinal inflammation and apoptosis. • elevated histamine content in diet reduced the variety and amount of the intestinal flora in hybrid grouper, leading to a decrease in the probiotic Cetobacterium and an increase in the pathogenic bacteria Ralstonia , Pseudomonas , and Prauserella , thereby compromising intestinal immunity. • The current study recommended that the amount of histamine in hybrid grouper feed not surpass 404 mg/kg.