Condensed tannins increased intestinal permeability of Chinese seabass (Lateolabrax maculatus) based on microbiome-metabolomics analysis

Condensed tannins (CT) have been reported to induce intestinal injury of fish, whereas the injury mechanism is unclear. This study evaluated the effects of dietary grape seed CT on growth, intestinal permeability, tight junction structure, intestinal digestive and brush border enzyme activity, bacterial community and intestinal metabolites of Chinese seabass (Lateolabrax maculatus). A total of 640 fish were randomly distributed into 16 tanks with 4 tanks per group and 40 fish per tank. Four diets were formulated to contain 0 (CT0), 1 (CT1), 2 (CT2), and 2 g/kg of CT plus 4 g/kg of polyethylene glycol (PEG) (CT2 + PEG). PEG specifically binds with CT to neutralize CT activity. The experiment was arranged as complete randomized design. Fish were hand-fed to apparent satiation twice daily and the feeding trial lasted for 63 days. Fish fed CT2 had lower (P < 0.05) final body weight, weight gain rate, specific growth rate and feed intake, but higher (P < 0.05) serum diamine oxidase activity and endotoxin level than other diets. Tight junction structures in CT1 and CT2 showed varying degrees of ambiguity and damage. The trypsin activity ranked as CT0 > CT1 > CT2 (P < 0.05). Fish fed CT2 had lower (P < 0.05) activities of lipase, amylase and creatine kinase than other diets. Na+, K+-ATPase activity was lower (P < 0.05) in CT1 and CT2 than in CT0. All parameters were similar (P > 0.05) between CT0 and CT2 + PEG. Intestinal microbiota analysis showed that the abundances of Bacillus, Acinetobacter and Pseudomonas were decreased (P < 0.05) but Clostridium was increased (P < 0.05) as dietary CT increasing. Fish fed CT2 + PEG had higher (P < 0.05) abundances of Bacillus, Acinetobacter and Pseudomonas but lower (P < 0.05) Clostridium than those of fish fed CT2. Bacterial diversity measurements were not affected (P > 0.05) by dietary treatments. Metabolomics analysis indicated that CT altered the intestinal metabolomics profile of L. maculatus. The valeric acid was decreased (P < 0.05), but phenylacetic acid was increased (P < 0.05) as dietary CT increasing. Compared to CT0, CT2 had lower (P < 0.05) isobutyric acid but higher (P < 0.05) butyric acid and isovaleric acid. In conclusion, this study suggests association between reduced growth and increased intestinal permeability and varying intestinal bacterial microbiota and metabolites of L. maculatus. This study warns that dietary CT at 2 g/kg could induce intestinal injury, microecological imbalance and metabolic disorder of fish, and the resulting adverse effects may neutralize by applying polyethylene glycol in fish diets.