Lead Exposure Induces Structural Damage, Digestive Stress, Immune Response and Microbiota Dysbiosis in Intestine of Silver Carp (Hypophthalmichthys Molitrix)

Lead (Pb) is one of the most common toxic heavy metals in water, and it can cause harm to aquatic animals and humans when released into the environment. In the present study, the effects of Pb exposure 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 could severely damage the intestinal morphology on the one hand, including significantly shortening the intestinal villi’s length, increasing the goblet cells’ number, causing the intestinal leukocyte infiltration, and thickening the intestinal wall abnormally, and 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 (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 was decreased, and the cellular antigens was increased. Finally, the canonical correlation analysis (CCA) found that there were correlations between silver carp’s intestinal microbiota and intestinal morphology and immune factors. In conclusion, it is speculated that Pb may damage the intestinal barrier of silver carp, leading the microbiota dysbiosis, which further affects the intestinal immune and digestive function.