ACUTE TOXICITY TEST TO DETERMINE THE EFFECTS OF COPPER, ZINC AND CYANIDE ON COBIA (RACHYCENTRON CANADUM) RESOURCES IN NORTH VIETNAM

Acute toxicity tests with copper, zinc and cyanide were conducted at Do Son Marine Station on the following various stages of development of cobia Rachycentron canadum: eggs, larvae (one-day-old fi sh), juveniles (20 days old) and young fi sh (40 days old). 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. The result also shows that cyanide was the most toxic to cobia, followed by copper and zinc. The fi sh responded immediately on exposure to the cyanide test solution even at low concentration. On the other hand, the effects of copper and zinc poisons were apparent throughout the fi rst 24 to 48 hours. The effect of copper was often fi ve to ten times stronger than that of zinc.