الفهرس 
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Abstract
It is known that river Nile and its branches are polluted with industrial, agricultural and sewage wastes. So, the current study was performed to declare the degree of pollution with mercury in fish and water of the river Nile at Gharbia Governorate.
Therefore, a total of one hundred samples of both Tilapia nilotica and Clarias lazera were harvested by fishermen by a means of a fishing net in Kafer El Zayat at Gharbia Governorate. Fifty random samples of Tilapia nilotica and Clarias lazera were harvested from the same area and divided into (25 of each small and large type) for detection of mercury in each type. The samples of both fish and water were examined using Atomic Absorption Spectrophotometer (Perkin Elmer, Model 2380, U.S.A.) and all values were reported as ppm (mg/kg) wet weight for fish samples and as ppm (mg/liter) for water samples. The results declare that the mean values of mercury concentrations in examined samples of Tilapia nilotica in small fish were 0.650 ± 0.076 ppm and in large fish were 0.868 ± 0.74 ppm, respectively, while the mean values of mercury concentrations in examined samples of Clarias lazera in small fish was 0.763 ± 0.071 ppm and in large fish were 1.000 ± 0.084 ppm, respectively. Sixty four (64%) percent of large fish of Tilapia nilotica harvested from Gharbia governorate contained mercury exceeded the safe permissible limits while (80%) of large fish of Clarias lazera harvested from the same governorate contained mercury exceeded the safe permissible limits. So, the result indicated that the (28%) of small fish of Tilapia nilotica and 56% of small fish of Clarias lazera contained mercury exceeding the safe permissible limits, respectively. The results declared that there were a significant differences between the levels of mercury in both of Tilapia nilotica (small and large) and Clarias lazera (small and large) fish types. Small Clarias lazera revealed 1.53+ and large Clarias lazera revealed 3.68+, while, small Tilapia nilotica contained 0.47+ and large Tilapia nilotica revealed 1.09. Furthermore, the results declared that the concentrations of mercury in water samples collected from Gharbia governorate ranged between 0.113 & 0.652 ppm with a mean value 0.347 ppm and these results were recorded in area (A) which far from the surface by 30 cm. Whilemean, the concentration of mercury in area (B) which far from surface by 50 cm was 0.285, 1.091 ppm with mean value 0.75 ppm. from the above mentioned results, the levels of mercury in Clarias lazera were more heighr than those in Tilapia nilotica which were harvested from the same area. Suggested recommendations were discussed to prevent the pollution of the Nile river with mercury, as a heavy metal, and for protection of fish for and consumers.