Nile tilapia Oreochromis niloticus fish exposed to different concentrations of chlorantraniliprole (CAP) as well as its mixture with ZnO-NP as a heavy metal pollutant at 10 µg/ml for four days. Additionally, the histological and biochemical constituents in Oreochromis niloticus, which can be employed as  biomarkers in monitoring aquatic toxicity were investigated. The 96 hrs.LC50 value of test toxicant to the fish found to be 10.607 µg/ml for CAP alone whereas the toxicity of CAP-ZnO-NP mixture (0.386 µg/ml) was 27- fold more. In vivo study, Nile tilapia fish exposed to sublethal concentration of chlorantraniliprole (1/10 LC50) to determine the toxic effect of the environmental contaminant on AChE, ALT, and AST enzymes. The histopathological effect of insecticide and its mixture with zinc on the gill and liver of freshwater fish O. niloticus were also determined by light microscope. The obtained results indicated that the brain of AChE activity of fish exposed to CAP was increased at the early period, 24h and 48h following treatment with CAP, while activities of liver enzymes named ALT and AST were significantly reduced. All enzymes were recovered after 14 days. Gills and liver were found to be seriously affected in comparison with the control. The gill of fish exposed to CAP-ZnO-NP showed numerous pathological changes, including oedema, epithelial lifting, necrosis, hyperplasia, lamellar disorganisation, and lamellar fusion. On the other hand, the liver showed fatty degeneration, increased sinusoidal space, cytoplasmic degeneration, necrosis, and focal fibrosis. These findings may be used as biomarker for water pollution and early warning ecotoxicological parameters for CAP if it would have interacted with another contaminant such as ZnO-NP in the environment.