Impact of Microcystin-LR exposure on biochemical responses, transcriptomic profiles, gut microbiota, and growth performance in grass carp (Ctenopharyngodon idella).

In recent years, Microcystin-LR (MC-LR) has been frequently detected in aquatic environments, exerting detrimental effects on the health of aquatic organisms. The grass carp (Ctenopharyngodon idella), an economically important fish, inhabits environments prone to MC-LR contamination. To investigate the toxicological mechanisms of MC-LR on grass carp, the fish were exposed to water containing 35.8 µg/L MC-LR. The physiological, biochemical, gut microbiota, and transcriptomic responses of the grass carp were evaluated at various time points (days 0, 1, 3, 7, and 21). The results showed that total superoxide dismutase activity in the liver and intestine was significantly increased after 21 days of exposure. Additionally, pathological damage was observed, including impaired intestinal epithelial barrier and nuclear pyknosis in the liver cell. MC-LR exposure also altered the diversity and composition of the gut microbiota and reshaped the microbiota interaction network, increasing the abundance of Cetobacterium and Vibrio by 32.43 % and 25.7 %, respectively. The intestinal microbiota functions were enriched in carbohydrate metabolism (10.45 %) and amino acid metabolism (9.89 %). RNA sequencing identified 504 shared differentially expressed genes (DEGs). The expression of the immune genes ITGB1 and GART was significantly upregulated in the D21 group. The upregulated DEGs were enriched in the complement and coagulation cascade pathways. MC-LR exposure induced metabolic disorders in grass carp, with upregulated genes significantly enriched in amino acid and carbohydrate metabolism pathways, while downregulated genes were enriched in lipid metabolism. This study provides valuable insights into the effects and toxicological mechanisms of MC-LR on aquatic organisms.