The conventional acute toxicity test; the fish bioasssay has been used extensively to determine the toxicity of samples tested. The principle of fish bioassay lies in the exposure of the fish of selected species to the test substance preferably for a period of 96 hours. Mortalities are then recorded at 24, 48, 72 and 96 hours and the concentrations which kill 50 percent of the fish (LC50) are determined where possible.