Acute Toxicity of Methyl Parathion on Freshwater Catfish, Heteropneustes fossilis (Bloch) Under Laboratory Conditions

Abstract

Methyl parathion, a highly toxic organophosphorus insecticide, is widely employed in agriculture. Runoff from these fields frequently pollutes freshwater ecosystems, endangering non-target aquatic life. This study assessed the acute toxicity of methyl parathion on the freshwater catfish Heteropneustes fossilis (Bloch) in a controlled laboratory setting. Healthy fish were subjected to varying concentrations of methyl parathion in static bioassay systems over a 96-hour period. Mortality rates, behavioral changes, and toxic symptoms were documented at 24, 48, 72, and 96-hour intervals. The median lethal concentration (LC₅₀) was calculated using probit analysis. Fish exposed to the chemical displayed hyperactivity, erratic swimming, and excessive mucus production, loss of balance, breathing difficulties, and surfaced frequently before dying. Previous studies have reported the 96-hour LC₅₀ value for H. fossilis to be approximately 7.0 ppm, indicating the species' high sensitivity to organophosphate pesticides. These findings reveal that methyl parathion poses substantial ecological threats to freshwater fish populations and can negatively impact aquatic biodiversity. The study underscores the importance of stringent regulation of pesticide application near aquatic habitats.