Three tilapia species; Oreochromis niloticus, Oreochromis aureus and Tilapia  zillii were evaluated as biomarkers for five different  organophosphorus pesticides (Diazenon,  Lindan, Parathion,  Malathion and Chlorpyrifos) at  Lake Edku, Egypt.  O. niloticus  reflected highest accumulated pesticides comparing with T. zillii, which reflected lowest accumulation levels of Diazenon,  Lindan,  Parathion,  Malathion and  Chlorpyrifos  respectively.  O. niloticus, O. aureus and T. zillii showed varied antioxidant activity patterns corresponding with pesticide accumulation levels. O. niloticus was superior for Superoxide  dismutase activity comparing with O.aureus and T. zillii, which reflected lower level respectively. Moreover, T. zillii reflected the lowest  Catalase  activity comparing with O. aureus that showed the highest activity. O. niloticus showed high glutathione  Peroxidase activity comparing with O. aureus and T. zillii. Glutathione reductase reflected distinguishable variation among O. niloticus, O. aureus, and T. zillii. Glutathione - S-transferase enzyme activity was decreased for T. zillii comparing with O.niloticus and O.aureus. As protein fraction, Glutathione S-transferase (GST) was expressed as one single band with different protein content. Glutathione S-transferase (GST) gene sequence of T. zillii reflected the highest genetic similarity (92.81%) with GST reference sequence. The lowest genetic similarity for GST gene sequence remarked   (75.29%) O. niloticus.  O. aureus  showed moderate genetic similarity (87.11%) comparing with the reference gene sequence.  It could be concluded that, significant correlation was detected among different  organophosphorus   pesticides accumulation and activity levels. Protein content and sequencing of  many antioxidant enzymes indicated promising potential of employing three Tilapia species O. niloticus, O. aureus and T. zillii as biomarkers.