Brain Acetylcholinesterase Activity as a Potential Biomarker for the Rapid Assessment of Chlorpyrifos Toxicity in a Euryhaline Fish, Oreochromis mossambicus

Acute studies of chlorpyrifos, O,O-diethyl-O-(3,5,6-trichloro-2-pyridyl) phosphorothioate insecticide on fish, Oreochromis (Tilapia) mossambicus, were carried out to assess the toxicity in relation to the marker enzyme, acetylcholinesterase (AChE, EC 3.1.1.7) activity in a semi-static system. Chlorpyrifos can be rated as highly toxic to O. mossambicus, with median lethal concentrations (LC50) of 43.52, 35.89, 30.6 and, 25.78 μg L−1 for 24, 48, 72, and 96 h respectively. The time required for 50% inhibition (IT50) of acetylcholinesterase (AChE) activities were measured in the brain of O. mossambicus, exposed to different median lethal concentrations indicated a decrease in time as the concentration increased. After exposure, survival fish were transferred to clean (chemical free) water and studied. AChE recovery were recorded in regular intervals of 3, 7, 14 and 21 days as a biomarker of exposure to this compound. The fish exposed to the LC50 for 24 h (43.52 μg L−1) showed a significant inhibition of AChE ...