Chlorpyrifos-methyl, a wide-spectrum organophosphorus insecticide and potential toxic pollutant contaminating
aquatic ecosystems, was investigatedfor acute toxicity. Larvae of the freshwater fish Nile tilapia (Oreochromis niloticus
L.) were selectedfor the bioassay experiments. The experiments were repeatedthree times andthe 96 h LC50 was determinedfor the larvae. The static test methodfor assessing acute toxicity was used. Water temperature was maintainedat
25 ± 1 C. In addition, behavioral changes at each chlorpyrifos-methyl concentration were observed for the individual
fish. Data obtainedfrom the chlorpyrifos-methyl acute toxicity tests were evaluatedusing Finneys probit analysis statistical method. The 96 h LC50 value for Nile tilapia larvae was calculatedto be 1.57 mg/l.