Oxidative damages and ultrastructural changes in the sperm of freshwater crab Sinopotamon henanense exposed to cadmium.

The toxicity of several waterborne heavy metals to aquatic organisms is associated with oxidative damages due to the formation of reactive oxygen species (ROS). In the present work, the reproductive toxicity of the heavy metal cadmium was tested with the sperm of freshwater crab. The crabs were exposed to sublethal concentrations of 0, 7.25, 14.5, 29, 58 and 116 mg/L of Cd²⁺ for 3, 5 and 7 d. Cd²⁺ accumulation, ROS formation, and the total antioxidant capacity (TAC) in Sinopotamon henanense sperm were measured. Biomarkers of oxidative damage to lipid (Malondialdehyde, MDA), proteins (protein carbonyl derivates, PCO) and DNA (DNA-protein crosslinks, DPC) were investigated to address Cd²⁺ effects on crucial macromolecules of the S. henanense sperm. Transmission electron microscopy (TEM) was applied to assess ultrastructural changes induced by 29 and 116 mg/L Cd²⁺ exposure for 7 d. The results showed that sperm Cd²⁺ levels were significantly increased at 3, 5 and 7 d starting from the 14.5 mg L⁻¹ Cd²⁺-treated groups. Meanwhile, ROS levels were significantly increased over the experimental period. In terms of TAC, statistically significant changes were observed only at day 7 with the Cd²⁺ concentrations of 14.5, 29, 58 and 116 mg/L. This resulted in an increase of MDA content (5 d and 7 d), PCO content (Cd²⁺: 58 and 116 mg/L, 7 d), and DPC levels (Cd²⁺: 116 mg/L, 3 d and 7 d), by 26.32%, 37.47%, 22.04%, respectively, in the 116 mg/L Cd²⁺ group at day seven. For ultrastructural observations, the sperm membrane became wrinkled and partly dissolved, the nuclear envelope turned wrinkled and the chromatin condensed, the acrosome was incomplete with a damaged acrosomal membrane in crabs treated with 29 mg/L Cd²⁺ for 7 d. After treatment with 116 mg/L Cd²⁺ for 7 d, the sperm membrane was almost dissolved, the chromatin in the nucleus was more heavily condensed, chromatin irregularities and serious acrosome damage were observed.