For the acute toxicity tests, prawns were exposed to copper concentrations ranging from 0.3 to 2.0 mg/l. The 96-h LC50 and its 95% confidence limit for P. merguiensis were 0.38 and 0.21-0.68 mg/l, respectively. P. monodon, on the other hand, exhibited no acute toxic effects in seawater, at or below a concentration of 2.5 mg Cu/l. The presence of dissolved copper significantly inhibited the growth ofP. merguiensis but not P. monodon. Both species accumulated copper during the experiment.