الفهرس 
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Abstract
The object of this study was to determine the effect of Boron (boricacid) and Cadmium (cadmium chloride) on Nile Tilapia (Orechromis niloticus) heat shock protein70 gene expression, activity of liver enzymes, body composition and histopathological alterations of liver and gills. The study was conducted through two phases, first was to determine the LC50 for boron and cadmium and this was by using five concentrations of boron (1,20,40,80,500 mgL-1) and four concentrations of cadmium (15,30,60,90 mg L-1) in addition to the control group, one replica for each concentration, the test continued to 96hrs. By the end the LC50 was calculated and tissue sections from liver were taken. The second phase was to study the chronic effect of boron and cadmium on the Nile Tilapia through using quarter dose of LC50. The experiment continued for 2 months and treatments were “control, with concentrations of 29 mgL-1 and 72.5 mgL-1 for boric acid, a concentration of 6.25mg L for cadmium, and combinations of (B 29 mgL-1 + Cd 6.25 mgL-1) and (B 72.5 mgL-1 + Cd 6.25mgL-1). Triplicates had been used and fish had been fed twice/daily on commercial diet 30% protein by 10%of its body live weight. By the end of the experiment total length, total weight and liver weight were determined, liver, gills and flesh section were taken for analysis body composition, heat shock protein70, activity of liver enzymes and other histopathological changes. Results showed that chronic influence of boron and cadmium on heat shock protein (Hsp70) in musculature, liver function, antioxidant enzymes, and histopathology of liver and gills. The relative expression of HSP70 in B29, B72.5, B29+Cd, B72.5+Cd, and Cd was P= <0.0001, P= 0.0018, P= 0.0198, P= 0.4573, and P= 0.9814, respectively, in comparison with the control group. Alanine aminotransferase (ALT), aspartate aminotransferas (AST), and alkaline phosphatase (ALP) enzymes activities demonstrated significant differences between treatments. Liver antioxidant enzymes catalase (CAT), superoxide dismutase (SOD), and glutathione peroxidase (GPx) activities showed significant differences between treatments. Histopathological investigation of fish liver and gills in treated groups revealed alterations and changes of normal structure as compared to control. Histochemical studies on liver using bromophenol blue and Periodic acid Schiff to identify general proteins and carbohydrates, in altered tissue both hepatocytes and hepatopancreatic acini were strongly stained and irregular distribution in glycogen and depletion were observed respectively.