Fish are particularly sensitive to a wide variety of agrochemicals including glyphosate herbicide 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 glyphosate an herbicide was investigated with emphasis on histopathological effects. Nile tilapias (Oreochromis niloticus) juvenile 15 ± 1.0 g were exposed to 0, 2, 9, 30, 97 and 310 mg/l of glyphosate. The lethal concentration (LC50) value of glyphosate was 1.05 mg/l for 96 h of exposure. Glyphosate concentration corresponding to the 96 h LC50 values for juvenile tilapia was used to study the effects of glyphosate exposure for 4 days in inducing histopathological changes of gills, livers, kidneys and brains. In the gills, filament cell proliferation, lamellar fusion, lamellar cell hyperplasia, and epithelial lifting were observed. In the liver, there was vacuolation of hepatocytes and necrosis. Kidney lesion consisted of hyaline droplets in the tubular epithelial cells and pkynosis. The brain lesion also consisted of generalized neuronal degeneration and spongiosis. The changes in these tissues 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. Glyphosate is highly toxic to Nile tilapias, which are more susceptible to this herbicide; therefore their use near fish farm or in area close to aquatic environment should be discouraged.
Key words: Nile tilapia, Oreochromis niloticus, glyphosate toxicity, histopathology.
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