Acute Toxicity of Copper, Cadmium, and Mercury to the Freshwater Fish Varicorhinus barbatus and

Acute toxicities of copper, cadmium, and mercury to the freshwater fish Varicorhinus bar-batus and Zacco barbata found in clear upstream waters were studied as a basis for the pro-tection of river water quality and the ease of aquaculture pond management. In all cases, the higher the concentration of metal used, the quicker the animals died. Twenty-four-hour LC50 values of copper, cadmium, and mercury to V. barbatus were 0.305 mg/l Cu, 1.657 mg/l Cd, and 0.183 mg/l Hg; however 96-h LC50 values decreased to 0.246 mg/l Cu, 1.502 mg/l Cd, and 0.168 mg/l Hg,respectively. Similarly, 24-h LC50 values of copper, cad-mium, and mercury to Z. barbata were 0.130 mg/l Cu, 2.598 mg/l Cd, and 0.201 mg/l Hg;96-h LC50 values were 0.079 mg/l Cu, 1.510 mg/l Cd,and 0.161 mg/l Hg,respectively. The order of metal toxicity to V. barbatus is Hg> Cu> Cd, while to Z. barbata it is Cu> Hg> Cd. To protect aquatic organisms, biologically safe concentrations of copper and mercu-ry are suggested to be 7 µg/l and 1.5 µg/l,respectively. However more studies are needed to determine this level for cadmium