There is no doubt that teleostean fish have attained great economic importance as a productive source of animal protein for human consumption. It was found that Random Amplified Polymorphic DNA (RAPD) analysis produced clear fingerprints from which the fish species could be easily identified. This approach offers the potential to detect fraudulent or unintentional mislabeling of these species in routine seafood authentication analysis. Aquatic contamination represents a constant source of public health concern. In Egypt, River Nile is the main water source and exposed to many kinds of pollutants.Biochemical markers are measurable responses to the exposure of an organism to xenobiotics. One of the most intensively studied biomarkers, in both laboratory and field conditions, is Cytochrome P450. Therefore, the aim of this work is to: 1-Employ RAPD-PCR method for detecting genetic variations withinfour tilapia species namely Oreochromis niloticus, Oreochromis aureus, Sarotherodon galilaeus and Tilapia zilli based on their ability to screen the variation in different parts of the genome. 2-Evaluate the effect of benzo-a-pyrene on the expression of CYP1A gene in Oreochromis niloticus.