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Diethyl phthalate (DEP) is used as plasticizer, detergent base in aerosol sprays, a perfume binder and it is known to be a contaminant of freshwater and marine ecosystem. The acute toxicity of diethyl phthalate to Clarias gariepinus fingerlings was investigated using static bioassays with continuous aeration over a period of 96h. The fish was treated with graded concentrations of DEP (0, 50, 75,100 and 150µg/1) to determine the LD50. The LD50 of DEP for Clarias gariepinus determined at 95% confidence limit after 24h, 48h, 72h and 96h. The LD50 after 24h, 48h, 72h and 96h were 2.22, 2.73, 3.44 and 3.93µg/l respectively. The mean LD50 was 1.87µg/l. There was no mortality in the control group but there was significant difference (P< 0.05) in the mortality in the treatment groups. The mortality which was dose dependent was 29.9% and 100% in 50µg/1 and 150µg/l DEP respectively. During the exposure period, the test fish was restless and swam erratically. Also, there was haemorrhaging of the gill filaments. These observations are indicative of stress due to effect of the diethyl phthalate on the fish.
Key Words: Toxicity, Clarias gariepinus, Diethyl phthalate, Stress, Mortality