الفهرس 
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Abstract
The aim of this study was to measure chemical, bacteriological, biochemical changes of fish to determine the pollutants level and their effects on the quality of catfish (Clarias gariepinus) and Oreochromis niloticus (are two of the most important fish species, widely distributed in Egypt and can persist in a highly polluted habitat and is possible to use as a potential bio-indicator for aquatic environmental contaminants). Therefore, Two sites in Egypt farms were chosen for the research, Damietta (site 1) and Lake Burullus (site 2).
The concentrations of heavy metals (Pb, Cd, Fe, Zn and Hg) were estimated in fish (muscles, gills, liver), sediments and water. Also, bacteriological analysis (total viable aerobic count, S.auerus, L.monocytogenes, E. coli, Salmonellae and coliform count) were estimated in fish (muscles, gills, liver). In addition, antioxidant parameter (Superoxide dismutase activity (SOD), malondialdehyde level (MDA), glutathione reductase, catalase, reduced glutathione (GSH), total anti- oxidant activity (TAO), and nitric oxide level). Also, differential leucocyte count (lymphocyte, neutrophil, monocyte, acidophil and basophil). In addition, serum protein, protein electrophoresis, RNA, DNA, RNA/DNA ratio, haemoglobin, WBCs, RBCs, heamatocrite. Finally, estimation of hepatosomatic index, liver water content, condition factor, moisture, lipid contents and total volatile nitrogen were determined in the fish.
Where, the obtained results showed that the contents of heavy metals in fish were depending on water and sediment contents of these metals. Also, depending on fish organs and sampling sites. Site 1 had greater concentrations of heavy metals Hg, Pb and Cd in water, sediment and tissues. While, Hg was not detected in site 2.
In the antioxidant parameter; there was increased in levels of MDA and nitric oxide, and reduced levels of SOD, GSH, catalase, glutathione reductase and TAO in fish samples of site 1. However, decreased levels of nitric oxide and increased levels of SOD, GSH, catalase, glutathione reductase, MDA and TAO occurred in fish samples of site 2. The results also revealed that, there was suppression of immune response in site 1. Immune response with these metals provides opportunities for the entry of pathogens and developing of many diseases in fish. Lipid contents, liver water content and total volatile nitrogen were highly elevated in fish samples of site 1. On the other hand, hepatosomatic index, condition factor, moisture, serum protein, RNA, DNA, RNA/DNA ratio, haemoglobin, WBCs, RBCs and heamatocrite were highly decreased in fish samples of site 1.