الفهرس 
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Abstract
The aquatic environment and its water quality are considered the main factor controlling the state of health and disease in fishes. Pollution of the aquatic environment by inorganic and organic chemicals is a major threat to the survival of fish O. niloticus. Monitoring Water quality has one of the highest priorities in environmental protection policy. The River Nile water is facing rising sources of pollution, as it receives a large quantity of industrial, agriculture and domestic wastewater, Rosetta Branch of River Nile is the most polluted part of River Nile. It is about 220 Km length and about 180 m width with average depth 2.0 to 2.3 m. It starts from EL-Qanater EL-Khayria and ends at Rosetta Estuary.
The physico-chemical characteristics of the aquatic environment directly influence the life inhabiting it. Fluctuations in these constituents create an adverse environment to organisms, limiting their growth and interfering in the physiological processes.
Among aquatic pollutants heavy metals regard as serious pollutants of aquatic ecosystem because of their environmental persistence and toxicity, the most commonly heavy metals in waste water are (arsenic, cadmium, chromium, copper, lead, nickel, and zinc), Heavy metals are dangerous because they bioaccumulate in fish, which may cause biochemical and morphological alterations, also causes changes in antioxidant defense system, which include enzymes such as (SOD, CAT, GPx, GST and GR),also the end product of lipid peroxidation (MDA).
So monitoring fish tissue contamination is important, it used as an early warning biomarker of aquatic pollution. Also, biochemical parameters may provide early warning indicators of general as well as specific toxicological responses. Biochemical biomarkers of contamination are important indices used in fish toxicity tests and for field monitoring of aquatic pollution.
Water and O. niloticus fish samples were collected from different sites form Rosetta Branch of River Nile, during seasons (spring, summer and autumn 2014 – winter 2015). Water samples collected from ten sites from El-Qanater El-Khyria before bifurcation (which selected as a referee site) to the area after industrial area Kafr El-Zayat city. Fish O. niloticus samples collected from three sites, (site I) El-Qanater El-Khyria before bifurcation (relatively unpolluted site), (site II) in front of Al Qata (polluted by El-Rahawy drain discharges) and (site III) in front of industrial area Kafr El-Zayat (polluted by industrial wastes). Twenty four (24) fish were collected seasonally from each sampling site, nearly the same size, length and weight. With average body weight (150 ± 10 gm.), and average body length (19 ± 5 cm).
Most of Physico-chemical parameters of water samples (Temperature, EC, TDS, pH, Transparency, DO, BOD, COD, NO2¯, NO3¯ and NH4+) and heavy metals (Fe, Zn, Cu, Mn and Cd) were within the permissible limits at site (1), indicating better water quality, so it used as referee site. Sites (3 and 9) recorded an elevation in most of physico-chemical parameter and exceeded the maximum permissible limits, Due to the effect of El-Rahawy drain and industrial area at Kafr El-Zayat.
The concentrations of Heavy metal (Fe, Zn, Mn, Cu, and Cd) in muscles of O. niloticus collected from Rosetta Branch of River Nile, displayed a significant increase in sites (II and III), where the maximum values were in winter. The accumulation patterns of heavy metals found in muscles of O. niloticus collected from Rosetta Branch of River Nile in the following order: Fe > Zn > Mn > Cu and Cd.
The bioaccumulation factor (BAF) follows the order: winter > autumn > summer and spring. The concentrations of heavy metals (Zn, Mn, Cu and Cd) in muscles of O. niloticus in the present study were below the maximum permissible limits except (Fe).
All antioxidant enzymes and MDA level showed a significant elevation in tissues of O. niloticus, and liver recorded a higher value than white muscles in all sites during all sampling seasons, especially in cold seasons.
Biochemical parameters (Glucose, Total protein, albumin, urea, creatinine, uric acid cholesterol, triglycerides, AST and ALT) in blood serum of fish O. niloticus showed a significant increase at all sites. Due to the negative effect of pollutants presents in water and their accumulation in O. niloticus tissues, which leads to consuming more energy and organs (liver and kidney) malfunction and increase their enzymes in blood stream.
It could be concluded from the present study that, water pollution have harmful effects on fish and alters the activity of the antioxidant defence system (SOD, CAT, GPx, GST, GR) and increase the risk of lipid peroxidation, also impaired the biochemical metabolites as: glucose, total protein, albumin, cholesterol, triglycerides, kidney function (urea, creatinine, uric acid) and liver function enzymes (AST and ALT).
The present study recommends a constant monitoring program for water quality of River Nile, in order to record any change in the quality and mitigate the outbreak of health problems, and the adverse impact on the aquatic ecosystem. Since the River Nile serve as source of drinking water and fish. Moreover, the River Nile water quality must be protected and improved as soon as possible.