الفهرس 
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Abstract
Cadmium, copper, lead and iron salts are usually found in agricultural and industrial liquid waste which discharged into water resources. These metals are toxic to aquatic life at low concentration; such metals may be accumulated from water to higher level in fish tissue. Metallothionein play a key role protecting cells against high levels of essential metals, as well as in detoxifying non-essential metals such cadmium. from this point of view we aimed to: 1- Determining the heavy metals residues in the tissue of O. niloticus fish. 2- Studying the effect of heavy metals contamination on Metallothionein gene expression using semi-quantitative RT-PCR.The study was focused on the determination of the bioaccumulation progress of some heavy metals (Cd, Pb, Cu and Fe) in different tissues (liver, brain, muscle and heart) of O. niloticus fish which represented by 2 fishery sites: Sample site 1: 90 Fish were collected from Bahr El-Baqar drain region which represented heavily polluted site with wastewater
Sample site 2:90 Fish were collected from El-Bahr El-Sagheir (tributary of River Nile) represented the less polluted site.
Each sample group was divided into three subgroups according to weight as follow:
Subgroup 1 : their weight ranged between 40-100 g (small)
Subgroup 2 : their weight ranged between 101-200 g (medium)
Subgroup 3 : their weight ranged between 200-300g (large)
where 30 individuals were used for each weight group obtained from each site.