الفهرس 
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Abstract
The environmental pollution is considered as one of the most serious problems in the world. Pollution of aquatic environments by metals is a world-wide problem due to the persistence and continuing accumulation of metals in environment. Mercury is considered to be of the most toxicologically problematic metals in fresh water environment. The present study was designed to evaluate the effect of temperature on the toxicity of mercury chloride in Nile tilapia fish by studied its effect on, serum biochemical parameters, oxidative stress parameters in liver tissue, mercury accumulation in muscle ,histopathological changes and effect of mercury and temperature on expression of heat shock protein.
-In this study 100 acclimated Nile tilapia fish (Oreochromis niloticus) were divided in- to 5 experimental groups 20 in each group.
-Preparation of stock solution by added 10 mg mercury chloride /L distilled water then use 0.022 mg/L of stock solution of Hg Cl2 (1/10 LC50) /L water in aquaria
-group I: Nile tilapia fish kept as control with water temperature 25 c°.
-group II: Nile tilapia fish was exposed to 0.022 mg/L of stock solution of Hg Cl2 (1/10 LC50) /L water in aquaria with water temperature 25 c°.
-group III: Nile tilapia fish was exposed toHg Cl2 (1/10 LC50) /L water in aquaria with water temperature 28 c°.
-group IV: Nile tilapia fish was exposed to Hg Cl2 (1/10 LC50) /L water in aquaria with water temperature 31 c°.
-group V: Nile tilapia fish was exposed to Hg Cl2 (1/10 LC50) /L water in aquaria with water temperature 34 c°.
The experiment was extended for 42 consecutive days.
Groups were observed daily Collection of blood samples were performed at21 and 42days of experiment. Blood samples centrifuged and obtained serum for biochemical analysis, Liver tissue was taken (259 mg/fish) kept for antioxidant activities measurement, Liver, kidney and gills samples were kept in formalin 20% for histopathological examination and dorsal muscle for estimation mercury residue and for determination heat shock protein (HSP 70) expression..
The results obtained in this study could be summarized of follows:
Regarding to the biochemical results ALT, AST ,creatinine and urea level showed highly significant increase in all exposed groups if compare with the control group and it increases gradually with increase in temperature. Total protein, albumin levels, SOD, GPX and CAT showed significant decrease these results were clear at group exposed to high temperature. Also Mercury residue in muscle showed significant increase in all exposed groups in compare to control. There were highly significant increase in exposed groups if compare with the control group and it increases gradually with increase in temperature. These results were clear at group exposed to high temperature and more pronounced at the end of experiment. There were highly significant decrease in exposed groups at 21 and 42 days of experiment if compare with the control group and it decrease gradually with increase in temperature. These results were clearer at group exposed to high temperature.
The histopathological examination of liver, kidney and gills revealed alternation in histological structure of these organs at 21 and 42 days of experiment as it showed sever congestion, necrosis in liver and kidney. Sever congestion was seen in gills after 42 days of experiment.
More elevation of temperature in Hg 1/10 LC50 at 34c° exposed group cause more exhaustion of antioxidant parameters .Results revealed significant decrease in SOD, GPX and CAT level.also significant increase in level of ALT, AST ,creatinine and urea indicate more liver and kidney damage. Moreover, high temperature increase mercury residue in muscle .sever congestion and necrosis were seen in liver and kidney .Temperature effect on incidence and severity of histological changes in liver and kidney. Gills showing sever congestion in arch, diffuse of goblet cell formation in the epithelial cells of rakers and ischemia and atrophy in the filaments and lamellae.
The expression of Hsp70s can be induced by many factors besides heat-shock, including environmental stresses, such as heavy metal contamination, chemical poisons and biological stresses. Hsp70 was over-expressed and it has physiological importance in a balanced immune response.HSP70 gene expression increased gradually with increase in temperature. These results were clear at group exposed to high temperature. These results were clear at group exposed to high temperature and more pronounced at the end of experiment.