Asian Journal of Fisheries and Aquatic Research

Fish are particularly sensitive to a wide variety of agrochemicals including herbicides that may arise from not only deliberate discharge of these chemicals into waterways but also from approved agricultural practices. In the present study, the toxicity of weed crusher (Paraquat dichloride) an herbicide was investigated with emphasis on histopathological effects. Clarias gariepinus juvenile (mean body weight of 3.54±1.61g) and averaged average length 6.55±2.23 cm were exposed to 0, 0.06, 0.08, 0.1, 0 .12, and 0.14ml herbicide per litre of water (ml/l) weed crush (Paraquat dichloride). The lethal concentration (LC50) value of Paraquat dichloride was 0.007ml/l for 96 h of exposure. Paraquat dichloride concentration corresponding to the 96 h LC50 values for juvenile Clarias gariepinus was used to study the effects of Paraquat dichloride exposure for 4 days in inducing histopathological changes of gills. In the gills, filament cell proliferation, lamellar fusion, lamellar cell hyperplasia, and epithelial lifting were observed. The changes in gills occur predominantly in the 96 h exposure. Respiratory stress, erratic swimming and instant death of fish were observed in exposed fish, which varied with the concentration of the toxicant and this showed that mortality increased with increase in concentration. Paraquat dichloride is highly toxic to Clarias gariepinus, which are more susceptible to this herbicide; therefore their use near fish farm or in area close to aquatic environment should be discouraged.