Linking Ecophysiological Alterations and Pesticide Bioaccumulation in Tilapia zillii Inhabiting Wadi El-Rayan Lakes, Egypt

Wadi El-Rayan lake system, a Ramsar-designated wetland is one of the most ecologically and economically important freshwater bodies in Fayoum Governorate, Egypt. This study investigated the seasonal and spatial variations in pesticide bioaccumulation and the associated physiological impacts on Tilapia zillii from Wadi El-Rayan lakes, Egypt. Twenty pesticide compounds—including organophosphates, triazoles, carbamates, and pyrethroids—were quantified in fish tissues. Significantly higher concentrations were detected in Lake 1 during winter, with compounds such as terbufos, malathion, and methyl parathion showing notable accumulation. Morphometric traits and relative organ weights indicated severe impairments in growth and organ function, particularly in Lake 2 fish, which exhibited reduced muscle mass along with enlarged gills and livers. The condition factor (K) also varied significantly across lakes and seasons, correlating with levels of contaminant exposure. These findings highlight the ecotoxicological risks posed by agricultural pollutants and emphasize the need for regulatory actions and continuous ecological monitoring.