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Heavy metal lead (Pb) is a primary pollutant that pollutes aquatic environments and can be enriched in aquatic animals. Here, the effects of waterborne Pb on grass carp (Ctenopharyngodon idella) within 96 h of exposure were detected, and the association between microbiota alterations in the intestines and water was analysed. Results revealed that the intestinal barrier was damaged, including the intestinal morphology change, the structure‐related genes (villin‐1 and Claudin‐7) expression down‐regulation, the antioxidant (GST and GSH‐Px) and immune‐related genes (TNF‐α and IL‐8) expression up‐regulation. The MiSeq sequencing data revealed a decrease in diversity and an increase in microbiota richness in the intestines and water after Pb exposure. Linear discriminant analysis (LDA) results revealed an increase in the dominant bacteria (P_proteobacteria and C_Gammaproteobacteria) in the water, which enriched bacteria in the intestines. Canonical correlation analysis (CCA) found that there were correlations between intestinal microbiota and water microbiota, intestinal structure morphology and immune factors. Based on these results, we speculated that the effects of Pb on the grass carp intestinal barrier may be related to changes in the intestinal structure of grass carp and the water microbial community. These findings improve our understanding of the effects of heavy metals on the fish–microbe relationships after polluting aquatic habitats. [ABSTRACT FROM AUTHOR]

Lead (Pb) is one of the most common trace metals in water, and its high concentration in the environment can cause harm to aquatic animals and humans. In the present study, the effects of Pb exposure (3.84 mg/kg) on the morphology, digestive enzyme activity, immune function and microbiota structure of silver carp (Hypophthalmichthys molitrix) intestines within 96 h were detected. Moreover, the correlation between them was analyzed. The results showed that Pb exposure on the one hand severely impaired the intestinal morphology, including significantly shortening the intestinal villi's length, increasing the goblet cells' number, causing the intestinal leukocyte infiltration, and thickening the intestinal wall abnormally, on the other hand, increasing the activity of intestinal digestive enzyme (trypsin and lipase). In addition, the mRNA expressions of structure-related genes (Claudin-7 and villin-1) were down-regulated, and the immune factors genes (IL-8 , IL-10 and TNF-α) were up-regulated after Pb exposure. Furthermore, data of the MiSeq sequencing showed that the abundance of membrane transport, immune system function and digestive system of silver carp intestinal microbiota all decreased, while cellular antigens increased. Finally, the canonical correlation analysis (CCA) showed that there were correlations between silver carp's intestinal microbiota and intestinal morphology and immune factors. In conclusion, it is speculated that the entry of Pb into the intestine leads the microbiota dysbiosis, affects the intestinal immunity and digestive function, and further damages the intestinal barrier of silver carp. [Display omitted] • Pb destroyed the intestinal barrier and affected the activity of digestive enzymes. • Pb induced intestinal microbiota dysbiosis in silver carp. • Pb changed the immune and digestive function of fish intestinal microbiota. • There was a correlation between the changes of bacteria and structure and function in intestine. [ABSTRACT FROM AUTHOR]