A 56-day feeding trial investigated the effects of dietary histamine on the antioxidant capacity, gastric and intestinal barrier functions, and growth performance of striped catfish (Pangasianodon hypophthalmus). Seven isonitrogenous (34.0% crude protein) and isolipidic (10.5% crude lipid) diets were formulated with supplemental 0, 15, 30, 60, 120, 240, and 480 mg/kg of histamine, named H0, H15, H30, H60, H120, H240, and H480 group, respectively. Results showed that the weight gain rate, specific growth rate, relative intestinal length in the H240 and H480 groups, and the condition factors in the H480 group were significantly lower than those in the H0 group. Intestinal total antioxidant capacity, peroxidase, catalase, superoxide dismutase, glutathione peroxidase, and glutathione reductase activities in the H480 group were significantly lower than those in the H0 group, whereas intestinal malondialdehyde content exhibited the opposite trend. Intestinal complement 3, complement 4, immunoglobulin M, and Recombinant Mucin 2 in the H480 group were significantly lower than those in the H0 group, in contrast to intestinal lipopolysaccharide content. Intestinal IL-10 gene expression in the H480 group was significantly lower than that in the H0 group, whereas the TNF-α, IL-1, IL-6, and IL-8 gene expression exhibited opposite results. Scanning and transmission electron microscopic observation of the gastrointestinal tract revealed severe damage to the gastric mucosa and intestinal epithelium in the H480 group. The abundance of Treponema in the histamine groups was significantly higher than that in the H0 group. These results indicated that high dietary histamine decreases intestinal immunity and antioxidant capacity, inducing digestive tract oxidative damage and ultimately decreasing the growth of striped catfish.

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Dietary non-starch polysaccharides (NSPs) broadly influence fish intestinal flora and physiological metabolism, but limited information is available on grass carp (Ctenopharyngodon idella). This study investigated the effects of different types of NSPs on the growth, nutrient metabolism status, gut microbiota, and serum metabolome of grass carp. Fish were fed with diets containing 4.4% insoluble NSPs (INSP), 9.24% soluble NSPs (SNSP), 13.64% NSPs (4.4% INSP + 9.24% SNSP, NSP) and non NSPs (FM), respectively, for 9 weeks. Results showed that dietary SNSP decreased protein efficiency ratio and serum protein content, but increased feed coefficient ratio, feed intake, plasma blood urea nitrogen content, and plasma aspartate aminotransferase activity (AST); conversely, dietary INSP decreased plasma AST activity. Dietary INSP and SNSP increased serum free cholesterol content. Dietary NSPs altered the abundance of dominant bacteria and serum metabolite profiles. The differential metabolites between groups were significantly enriched in amino acid synthesis and metabolic pathways. In conclusion, dietary INSP exhibited a growth-promoting effect compared to SNSP. Dietary INSP is beneficial for improving nutrient metabolism and intestinal health. Moreover, dietary NSPs may regulate the physiological metabolism and feeding behavior of grass carp by altering amino acid synthesis and metabolism.