الفهرس 
Introduction and review of literatureOnly 14 pages are availabe for public view
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Abstract
A total of 1520 specimens of the cichlid fish; Oreochromis niloticus, O. aureus, Sarotherodon galilaeus and Tilapia zilli and clariid catfish, Clarias gariepinus were examined at seasonal intervals in the three sites between summer 2012 to spring 2013 from three sites, River Nile is represented by two sites: Beni-Suif City (Beni-Suif Governorate, 115 Km south to Cairo) and El-Mansoura City (El-Dakahlia Governorate, 120 Km north to Cairo) and the third site in the nourthern brackish, Lake Manzala (El-Dakahlia Governorate, 170 Km north to Cairo). from the study it can be concluded that: 1- During summer, the prevalence mainly showed its maximium values of different fish species at different study sites, followed by a gradual decline during autumn and reaching its minimium values during winter, then followed by increase of the prevalence values noticed in spring season. 2- The prevalence and mean intensity values of differet parasites in cichlid fish, O. niloticus, O. aureus, S. galilaeus, T. zilli and clariid catfish, C. gariepinus display higher values in River Nile (Beni-Suif El-Mansoura) comparing with Lake Manzala. 3- The results showed that, the prevalence and mean intensity values of crustacea and acanthocephala were nil in Lake Manzala during the investigation period. 4- The disappearance of some parasites in Lake Manzala may be due to the relatively high levels of some heavy metals, pH, electrical conductivity (salinity), minerals, ammonia, nitirites and nitrates. 5- It was evident that water temperature, pH value, dissolved oxygen, chromium, calcium, bicarbonates, potassium and total dissolved phosphorus showed high significant correlations with the prevalence and mean intensity values. 6- Parasites can be considered as suitable tools to investigate host ecology, where the close relationships between the parasitic organisms and their hosts may lead to use of parasites as biological indicators for environmental pollution. 7- Strict control enforced by laws regulation should be applied over polluted industrial wastewater, agricultural drainage water and sewage water debouches into the River Nile and Lake Manzala. All these sources of water input affect the physiochemical characteristics of water, sediments, biological components, fish production and human health.