Abstract
Oreochromis niloticus was exposed to glyphosate-based herbicide Excel Mera 71 for 30 days under field and laboratory conditions to investigate the histopathological and ultrastructural responses in gill, liver, and kidney. Gill displayed degenerative changes in the pillar cells of gill epithelium, curling of secondary lamella, and appearance of globular structure in laboratory condition under light microscopy. Scanning electron microscopic (SEM) observations revealed loss of microridges, disappearance of normal array of microridges, and damage in stratified epithelial cells under both the conditions, while severe vacuolation and necrosis were prominent under transmission electron microscopic (TEM) study in the laboratory condition. In liver, excess fat deposition and acentric nuclei in the laboratory condition were prominent under light microscopic and SEM study. TEM study showed necrosis in mitochondria, cytoplasmic vacuolation, degeneration in endoplasmic reticulum (ER), and reduced amount of glycogen droplets, but under field condition, lesions were less. Kidney showed fragmented glomerulus, excessive fat deposition, and hypertrophied nuclei under light microscope, while topological study showed shrinkage of glomerulus and degenerative changes under laboratory condition. TEM study also confirmed necrosis in mitochondria, dilation and fragmentation of ER, and appearance of severe vacuolation in the laboratory study, but no significant alterations were observed in field under SEM and TEM study. Therefore, the present study depicts that Excel Mera 71 caused comparatively less pathological lesions under field than laboratory condition, and finally, these responses could be considered as bioindicators for toxicity study in aquatic ecosystem.