The experiments were repeated three times for each treatment and each life stage of cobia. The result shows that for copper and zinc, the early stages are more sensitive than the later stages, and it is the converse for cyanide. Young fi sh are most sensitive to cyanide, with an LC50 value of 0.03 mg/L CN. The larvae and egg are most sensitive to copper and zinc, with LC50 values of 0.06 mg/L Cu and 0.313 mg/L Zn, respectively.