Abstract:The acute toxicities of trichlorfon on juvenile tilapia(♀Oreochromis niloticus×♂O.aureus)cutured in aerated tap water(pH=6.5)and pond water(pH=8.5)were studied at water temperature of(23.5±2.0)℃ and dissolved oxygen above 5 mg/L using a static bioassay test.The results showed that:(1)Under the condition of aerated tap water,the median lethal concentration(LC50)of trichlorfon on juvenile tilapia was 3.68,3.31,2.05 and 1.57 mg/L at 24 h,48 h,72 h and 96 h,respectively,and its safe concentration(SC)was 0.157 mg/L;(2)Under the condition of pond water,the LC50 of trichlorfon on juvenile tilapia was 0.35,0.29,0.17 and 0.13 mg/L at 24 h,48 h,72 h and 96 h,respectively,and its SC was 0.013 mg/L.The results showed that the toxicity of trichlorfon on juvenile tilapia cultured in pond water was stronger than that on juvenile tilapia cultured in aerated tap water.