We selected 5 days treatment to further analyze the methylation levels of CpG islands with MspI/HpaII ethidium bromide assay. Exposure of C. auratus to 2,4-DCP (0.01, 0.10 and 1.0 mg/L) led to the significant low ratios of HpaII/MspI (P < 0.05) (Fig. 2), which indicated that the methylation levels of CpG islands were significantly higher than those of control. In particular, 1.0 mg/L concentrations of 2,4-DCP increased the levels of CpG islands by 1.27-fold.