Ethion-induced Tissue Damage in Tilapia Oreochromis mossambicus (Peters, 1852): A Histopathological Insight

Abstract

Aquatic ecosystems are increasingly threatened by agrochemical contamination, particularly from organophosphate pesticides introduced through agricultural runoff and industrial effluents. This study investigated the acute toxicity and histopathological effects of Ethion [O, O, O′, O′-tetraethyl-S, S′-methylene bis (phosphorodithioate)] on Oreochromis mossambicus (Mozambique tilapia), an ecologically and economically important freshwater fish species. The median lethal concentration (96-h LC₅₀) of Ethion was determined to be 0.271 ± 0.10 mg/L, indicating high acute toxicity. Fish exposed to sublethal concentrations (0.027, 0.054, and 0.081 mg/L) exhibited pronounced behavioral alterations, including erratic swimming, hyperactivity, and loss of equilibrium, reflecting neurotoxic effects associated with acetylcholinesterase inhibition. Histopathological examination revealed progressive, dose-dependent tissue alterations across vital organs. Gills showed epithelial lifting, lamellar fusion, and necrosis, indicating impaired respiration and osmoregulation. The liver exhibited cytoplasmic vacuolation, sinusoidal dilation, nuclear pyknosis, and necrosis, suggesting hepatocellular degeneration and disrupted detoxification. Renal tissues demonstrated glomerular shrinkage, tubular necrosis, and inflammatory infiltration, reflecting impaired ion regulation and excretory dysfunction. The presence of enlarged melano-macrophage centres indicated activation of defence mechanisms against oxidative stress. These findings demonstrate that Ethion exposure causes severe structural and functional impairments in O. mossambicus, even at sublethal concentrations, underscoring the ecological risks posed by organophosphate contamination. Histopathological biomarkers observed in this study provide a sensitive diagnostic tool for assessing pesticide-induced toxicity in aquatic organisms and can aid in establishing safe environmental limits for pesticide usage.