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The detection of organophosphate (OP) insecticide pollution in natural waters requires knowledge of the physiological target sites and the mechanism of action of these chemicals in fish. This study was designed to determine the acute lethality of acephate (ATE), a phosphoramidothioate, and fenitrothion (FTN), a phosphorothionate, on rainbow trout fingerlings at three test temperatures; the sublethal effects of ATE and FTN on heart rate (HR), ventilation rate (VR), buccal amplitude (BA), and cough frequency (CF) in adult rainbow trout; and the effects of ATE and FTN on the brain, erythrocyte, gill, heart, serum, and skeletal muscle cholinesterase inhibition (ChEI) in these fish. From our results, the LC50 values of ATE were approximately 600 to 1000 times greater than those of FTN. Temperature affected the LC50 values, median survival times, and slopes of mortality curves of FTN, but not those of ATE. Both insecticides produced a decrease in HR, and an increase in VR and BA. FTN produced an increase in CF, but ATE did not. The cholinesterase activity in the erythrocytes, gill, heart, and serum showed marked inhibition after 3 h of exposure to ATE, compared with 1 h of exposure to FTN. More time was required to attain maximal inhibition in the brain and skeletal muscle than in other tissues. This study indicates that the cardiovascular and respiratory systems in fish are important sites of action for OP toxicity, and that this toxicity depends on physicochemical properties, for example, lipid solubility, and on environmental factors, for example, temperature.
absorption, acephate, aquatic toxicology, biochemical sites, biotransformation, cardiovascular system, respiratory system, cholinesterase, distribution, fenitrothion, organic phosphates, physiological mechanisms, temperature
Research scientist, National Inland Fisheries Institute, Kasetsart University, Bangkhen, Bangkok
Research scientist, Environment and Fisheries Canada, Freshwater Institute, Winnipeg, Manitoba, Canada