The present study was initiated to assess the levels of Fe, Mn, Zn. Cu. Ni. Co. Pb and Cd together with Na, K, Ca and Mg in liver and muscle of Tilapia zillii from three different aquatic ecosystems namely. Lake Manzaiah (Brackish water). Lake Qarun (Saline water) and El-Salam Canal (fresh water) and Oreochromis niloticus from Lake Manzaiah and El-Salam Canal throughout four seasons (1999-2H00). The present results revealed that liver has higher tendency to accumulate Fe and Cu more than the other studied heavy metals for O. niloticus and T. zillii in different studied sites. Zn followed Fe in the accumulation abundance in muscle tissues of the two studied species and Cd was the lowest one. The fluctuation of metal concentrations in muscle tissues for O. niloticus and T. zillii exhibited the following descending order
Fe>Zn>Mn=Cu-Ni=Co=Pb>Cd. while the abundance order of the same metals in liver tissues was: Fe>Cu>Zn>Mn>Ni>Co= Pb>Cd.