Acute toxicity of the chloroacetanilide herbicide butachlor and its effects on the behavior of the freshwater fish Tilapia zillii

-1 , respectively. There were significant differences (p<0.05) in the LC50 values obtained at different exposure times and the safe levels estimated by different methods varied from 1.25×10 -1 to 1.25×10 -5 mgl -1 . There were dose and time dependent increase in mortality rate due to exposure to the herbicide. Stress signs in form of hyperactivity, erratic swimming, skin discoloration, vigorous jerks of the body followed by exhaustion and death were observed. The 96 h LC50 of 1.25 mgl -1 obtained indicate that the herbicide was toxic to T. zillii. Agricultural use of butachlor in the environment, especially, near water bodies, must be restricted to avoid the severe risk associated with the use of the pesticide.