Acidification exacerbates lead-induced toxicity in crabs: Oxidative stress, microbiota disruption, and dietary...

The combined effects of water acidification and lead (Pb) pollution have become a significant ecological risk factor for freshwater aquaculture systems. In this study, we systematically evaluated the effects of acidification and Pb exposure on juvenile Eriocheir sinensis through three interrelated laboratory experiments. First, the effects of different pH levels (7.8, 6.5 and 5.5) and of Pb (1.435 mg/L), alone and in combination, on bioaccumulation, tissue damage, antioxidant enzyme activity and gut microbiota composition were investigated. In addition, a plant-derived feed additive (FYK) was applied to assess its mitigating potential under a representative combined stress condition (pH 6.5 + Pb). The results indicate that Pb accumulated in the gills and hepatopancreas of E. sinensis, with significantly increased bioaccumulation in these tissues at low pH (P < 0.05). Combined exposure to low pH and Pb resulted in severe histopathological damage, including gill lamella distortion, epithelial necrosis and hepatopancreatic cell vacuolation. Antioxidant enzyme activities were also significantly altered. SOD, CAT and GSH-PX activities increased with Pb exposure, but decreased with acidification, suggesting that acidification impaired the antioxidant defence capacity of juvenile crabs under Pb stress. Pb exposure altered the structure of the gut microbiota, reducing the abundance of key groups such as Candidatus Bacilloplasma. Notably, dietary supplementation with FYK, particularly at 1%, significantly alleviated tissue damage, improved antioxidant and immune-related enzyme activities, and enhanced stress tolerance. This study provides new insights into the effects of water acidification and Pb pollution on crustaceans, offering a scientific basis for the management of aquaculture water and the development of functional feed.