Abstract
An attempt was made to evaluate histopathological changes in the gills, liver, and kidney tissues of the freshwater teleost Oreochromis niloticus as biomarkers of chlorpyrifos toxicity. An experiment was conducted in glass aquaria with O. niloticus exposed for 28 days to sub-lethal concentrations of chlorpyrifos of 0.0 µg L−1 (control), 10 µg L−1, and 20 µg L−1. Chlorpyrifos caused distortions of the primary gill lamellae structure, the curling of secondary lamellae, desquamation, and epithelial hyperplasia on secondary gill filaments. Hepatocyte vacuolation and nuclear membrane necrosis were found in the liver. Additionally, the shrinkage of the glomeruli, thickening of Bowman’s capsule, glomerular and tubular necrosis, intracytoplasmic vacuoles, and hyaline degeneration in the renal tubule were seen in the kidney of O. niloticus exposed to chlorpyrifos. No remarkable lesions were observed in the control group. The severity of lesions in the fish tissues was assessed using the standard semi-quantitative grading system. The degree of histopathological lesions in various fish tissues was found to increase with chlorpyrifos concentrations. Histopathological lesions appeared to be good biomarkers of chlorpyrifos toxicity.