This study was undertaken to evaluate the impact of short-term and long-term exposure to the herbicide thiobencarb, wh*ehr4s~tege^ ;$ged~^"M^^-GQnta^ rice cultivation in Egypt,., on ^Ue tilapia; Orepchromis niloticusrLQi[\d\ and sublethal effects of thiobencarb on physiological, biochemical and histological parameters were also studied on the fish as a function of exposure time. Exposure of O. niloticus to lethal and sublethal levels of thiobencarb resulted in significantly (PO.05) lower values for liver and muscle glycogen, total protein and total lipids compared with the control group. In contrast, there was a significant increase (P<0.05) in muscle ash, water content, glucose, cholesterol, creatinine, Uric acid and Lactate dehydrogenase (LDH) in the herbicide-treated group, while aspartate aminotransferase (AST) and alanine aminotransferase (ALT) showed a fluctuated activity in both of acute and chronic exposure. The data indicated that the residue of thiobencarb had a higher value in the liver, while the lowest value was in the brain, Histological sections in gills, kidneys, spleen and liver of treated fish revealed pathological alterations. Cytotoxicity assessment was also included. Fish exposed to thiobencarp showed a significant reduction in growth parameters. The genetic investigations showed breaks, gaps, centromeric attenuation, centric fusion and deletion were the common aberrations. The mean percentage of aberrations were timedependent.