Bioaccumulation and physiological responses in juvenile Marsupenaeus japonicus exposed to cadmium

The heavy metal cadmium readily accumulates in organisms, causing damage. In this study, juvenile marine shrimp Marsupenaeus japonicus were exposed to cadmium (Cd²⁺; 5, 50 and 500 μg L^-1). Cd accumulation and antioxidant-related indices were determined, and damage to biomolecules was assessed, after 24, 48 and 96 h. Cd bioaccumulation in M. japonicus increased with exposure time and concentration, which reached the highest value at 96 h. The data showed that 5, 50 and 500 μg L^-1 Cd increased glutathione (GSH) content and the activities of superoxide dismutase (SOD) and glutathione S-transferase (GST) in a Cd-dose-dependent manner, but 5 and 50 μg L^-1 Cd had no effect on caspase-3 activity. The expression levels of SOD, GST, heat shock protein 70 (HSP70), metallothionein (MT), p53 and caspase-3 genes were rapidly increased after 50 and 500 μg L^-1 Cd exposure, and remained at a significantly higher level than in the control after 96 h of exposure. After exposure to 5, 50 and 500 μg L^-1 Cd, F-value (the ratio between double-stranded DNA and total DNA) remained high at 24 h, however, as the exposure time increased, the F-value decreased in a dose-dependent manner. An increase in malondialdehyde content was also observed following exposure to 50 and 500 μg L^-1 Cd. Our data suggest that Cd induces oxidative stress, molecular damage and apoptosis in juvenile M. japonicus in a concentration- and time-dependent manner.