Neurotoxicity induced by herbicides Almix and Excel Mera 71 in the Indian teleost Heteropneustes fossilis (Bloch)

Population explosion and simultaneous rapid loss of cultivable land escalated the use of pesticides and herbicides to ensure food security. However, uncontrolled application of toxic pesticides/herbicides, particularly organophosphorus and sulfonylurea, has resulted in increased mortality and morbidity worldwide. The present study reports the neurotoxic effect of herbicides Excel Mera 71 and Almix based on brain histopathology of the Asian stinging fish, Heteropneustes fossilis (Bloch). Herbicides, Excel Mera 71 (17.2 mg/L) and Almix (66.67 mg/L) were administered to fish for 30 days. Study showed several endpoints in optic tectum with varying degree. Spongiosis, binucleated nuclei, congestion, necrosis, enlarged pyramidal cells (EPC), neuronal degeneration, vacuolization, gliosis, aberrant horizontal cell orientation and granular cells were prominent pathological symptoms in optic tectum in Excel Mera 71 and Almix-treated H. fossilis. Among the six layers, SPV (stratum periventriculare) and SAC (stratum album centrale) layer were maximally impacted by herbicide exposure. Appearance of neural necrosis, gliosis, vacuolization and loss of Nissl substances, collectively called neurotoxicity indicators, were very prominent under herbicides treatment. Higher prevalence of these lesions under Excel Mera 71 indicated that this herbicide has higher neurotoxic potential than Almix. Additionally, mean assessment value (MAV) indicated highest pathological lesions in Excel Mera 71 (4.06 ± 0.02), followed by Almix (3.28 ± 0.10) compared with control fish (0.09 ± 0.04). Collectively, these alterations indicated that both herbicides caused adverse effects on brain metabolism including sensory modalities, visual appearances, and motor coordination. Accordingly, brain optic tectum pathological changes can be utilized as biomarker of neurotoxicity evaluating of environmental toxicants.