The toxicity to Clarias lazera of copper and zinc applied jointly.

1. The acute toxicity to juvenile Clarias lazera of a mixture of copper and zinc over a 96 hr exposure period was determined. Fish were exposed to the summation of half the 96 hr TLm value of each toxicant. 2. Percentage survival was much reduced indicating that the metals potentiate each others lethal action. 3. Comparison between metal residues in fish exposed to copper and zinc or to their mixture showed that the uptake of one metal was decreased by the presence of the other. 4. Toxic effects of the mixture on the physiological parameters studied were mainly attributable to copper, indicating that the presence of zinc did not influence the mode of action of copper.