Biochemical, histological and ultrastructural alterations of the alimentary system in the freshwater crab Sinopotamon henanense subchronically exposed to cadmium.

Cadmium (Cd) is one of the toxic metals in the aquatic environment. We investigated the effects of Cd on the digestive enzymes, antioxidant enzymes, malondialdehyde (MDA) content and morphology of the hepatopancreas and intestine in the freshwater crab Sinopotamon henanense. Crabs were exposed to sublethal Cd concentrations of 0, 0.725, 1.450 and 2.900 mg/L for 21 days. After Cd exposure, the activities of maltase, amylase and trypsin of two tissues were lower than the control. The activities of superoxide dismutase, catalase and glutathione peroxidase in the hepatopancreas and intestine were decreased, and the MDA concentration increased in all of the treated groups, over the experimental period. The results of light and transmission electron microscopy showed that 2.900 mg/L of Cd exposure caused profound morphological damages in the hepatopancreas and midgut. After exposure, histological abnormalities of two tissues were discovered, including cellular swelling and necrosis. Additionally, alterations in microvilli, nucleus, mitochondria, rough endoplasmic reticulum as well as Golgi complex in epithelial cells of two tissues were observed. This may be due to antioxidant enzymes activities that were reduced by Cd in the alimentary system of the crabs, and led to membrane lipid peroxidation. The membrane structure was destroyed, and caused further tissue damage, which likely made the alimentary system unable to secrete digestive enzymes, leading to further reduction of digestive enzymes.