الفهرس 
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Abstract
The Nile is consider to be the principle artery for Egyptian life. It is to be noted that, its branches and irrigation canals have been subjected over the last decades to the attack of industrial wastes as a direct results of several factories constructed very near to its banks, which would certainly lead to intensive accumulation of heavy metals in fish flesh and many changes in the water body from being clean oligotrophic to an alarming case of eutrophication. The present study has been initiated to determine the physicochemical characteristics of water, the distribution of some heavy metals in water, biochemical composition of fish flesh, heavy metals accumulation in fish flesh and the histopathological changes in some organs of Oreochromis niloticus caught from different stations. Four station have been selected along the Damietta branch for the collection of water and fish samples. These are El-Kanater, Benha, Zefta ant Talkha [El-Mansoura] stations. The water samples were collected monthly from January to December (1997) from the sub-surface layer. Fish samples were collected seasonally during the same year. The experiments in this research were carried out as follows : I-Water analysis: (A)Physical characteristics l-Air and watertemperature: Air temperature recorded clear changes at the studied area, it recorded a maximum value in August, (31;8°C), and a minimum one in March, (16.°C). This changes is related to the differences in collection time. Water temperature showed clear changes. They are ranged between (16.1°C) at Benha station and (31. 4°C) at El-Kanater station. 2-Transparency: Transparency values recorded wide fluctuations between 42 em _at El-Kanater station in July and 190 em at Talkha station in November. These falues werehigher in the cold monthes because of the less contain of the suspended matter. The transparency values depend alsolon increasing phytoplankton blooms and water turbidity. B-Chemical characteristics I-pH The pH values showed wide range between 6.9 in July at Talkha station and 8.79 in October at Benha. This change related to _the clear activity of phytoplankton arid the higher oxygen concentrations. Lower pH values were recorded in summer, which are due to the bacterial decomposition of organic matter. 2-Alkalinity :
The carbonate alkalinity values were ranged from, O.0 to 20. 0 mg CaCo3r1 and the bicarbonate alkalinity values were ranged from 80.0 to 216.0 mg CaCOjr1 for the different stations. The highest bicarbonate value was recorded in January, and the lowest value was observed in December.
3-0xygen studies
a-Dissolved oxygen:
Talkha station showed the lower values of the oxygen content. That they decreased to (4mgr1) in June which are due to the exhausting of oxygen in oxidizing the organic matter but at El-Kanater station at recorded the highest values of 15.2 mgl” in May because of increasing phytoplankton flourishing.
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b-BiologicalOxygen Demand: (BOD).
The values of BOn recorded the highest value in November at El-Kanater station•.while the lowest value was observed in May at Talkha station. The BOD values were related to the higher values of the dissolved oxygen.
c-Chemical Oxygen Demand (COD).
The maximum value of the COD was obtained in February at El-Kanater station, 28.00 mgl” and the lower minimum values in March and April 4.00 mgl” at Talkha station. The partial oxidation of organic matter which weakly takes place, causes the higher values of COD.
4-Nutrient salts:
a-Ammonia : Ammonia represented higher vaJlues at all stations. This is attributed to the increasing in the quantities and various kinds of wastes at the studied stations. The maximum value was 1.7 mgl-l was observed in August at Talkha station, while the minimum value of 0.1 mgl-l was recorded in February at El-Kanater station.
b-Nitrite:
Nitrite values changed from 1.9 to 43.2 J.l.gr1.The maximum value was recorded in December at Talkha station. This is because of the reduction of nitrate to nitrite or the oxidation of .ammonia to nitrite. The minimum value was recorded in February 1.9 Ilgr1 at EI-Kanater station.
c-Nitrate : i
Nitrate valuJs• changed from 5.98. t 242.9 Ilgr1. The maximum value was observed in November at Zefta station and the minimum value was recorded in September at El-Kanater station. The agricultural runoff contain nitrate fertilizers from near lands, is considered one of the important causes of increasing the concentration of ni,trate.
S-Heavy metals of water :
The four metals measured are Iron, Zinc, copper and lead. Their concentrations changed from one site to another through the studying period. The concentration of iron was changed from 0.43 to 0.90 mgl”, zinc from 82. To 180 ugl”, copper from 1(j.6 to 29.3 Jtg/L and lead from 9.0 to 32.3 J.1g1L. The higher values differ from one metal to another because of changing the stations, the quantities and kind of waste and the concentration of every metal. The maximum values of all metals were recorded at Talkha station, because, it exists in the zone of the agricultural and industrial activity.
II-Biochemical studies:
IL l-Biochemical composition
The main biochemical contents in the flesh of Oreochromis niloticus were determined at El-Kanter, Benha, Zefta and Talkha stations. The obtained results revealed that:
I-Water content:
Two maximum values were obtained for fish caught from El-Kanater and Benha stations during the summer season, being (86.9%), the while minimum value was obtained at Talkha station during spring being (79.1 %). It is to be noted that the water content showed an increase before immature than in mature fish.
2-Protein content:
The maximum values of the protein content in fish flesh were recorded during spring at Benha and Zefta stations being (87.5%, 88.0%). The minimum values recorded during autumn at the other stations, specially in the mature fish male or female,
3-Lipid content:
The maximum: value of the lipid content was recorded during the autumn season at Benha station specially in the mature fish, being (15.3%). The minimum value was recorded at all the other stations in spring, it was (15.3%). The minimum value was recorded at all the other stations III spring in the fishes, which were immature.
4-Ash content:
The present results showed that the higher value of ash existed was obtained in fish caught from El-Kanater station during autumn in the mature fish, being 10.9%. The lowest value was at Talkha station during summer in immature fishes being (3.7%).
5-Carbohydrate content:
The maximum value of carbohydrate content in fish flesh was obtained at El-Kanater station being (4.3%) in the male mature fishes during the summer. The minimum value was at Zefta station (0.1%) in the immature fishes, being (3.7%). As a general the present results indicate that the minimum values for the main biochemical constituents of fish flesh were obtained for those fish caught from Talkha station, which may be attributed to the increase in the concentrations of the heavy metals in water at this area than other studied areas.
Il.Z-Heavy metals accumulation injishjlesh :
The concentration of the heavy metals measured in water and also in fish caught seasonally from the studying station area of investigation, showed a great fluctuation according to the area. Fish caught from El-Kanater station, the concentration of Fe showed the maximum value (320 mg/g) during the summer season, however lead was found to be (11.67 mg/g) during the spring. Fish caught from Talkha station showed the maximum concentration of copper (9.6 mg/g). This is may be attributed to the fertilizers of Talkha factory during the summer. Fish caught from Benha station showed the maximum concentration of zinc (45.6 mg/g) during the spring. All these fluctuations may be due to the difference and kind of waste (industrial or agricultural). Therefore it can be considered, that the accumulation of the studied heavy metals in fish flesh (O.niloticus) are accepted as edible fish, although these are notable increase in the concentrations of Fe and Zn respectively.
III-Histological study:
Samples of fish Oreochromis niloticus fishes were seasonally collected from El-Kanater, Benha, Zefta, and Talkha stations, we had dissected them after catching directly. We had collected samples of gills, liver, muscles and gonads [ovary and testes].
l-Gills:
During the dissection, we observed that the gills had a light red color, which covered with a mucous layer. The histological studies had great and observable effect on the gills of fishes on which we made the study. This may be attributed to resulted from the great effect of pollutants in water along the River Nile .especially at the studied stations. The following effects are.
5-Testes:
The precise histological study showed a sparation between the testes wall and some parts of it, destruction for some spennatocytes at all stages and the other cells appeared in a good case to form the sperm. So we observed that there was a great effect on the ovary more than on the tests. In general, we observed that the morbid states had appeared severely in fishes, which are located Talkha station especially in summer and autumn. This is can be attributed to the increasing in the concentration of heavy metals, ammonia, nitrite, and reduced DO in the water at this station. from these results, we conclude that the Oreochromis niloticus fishes which located at the River Nile (Damietta branch) have been affected severely because of polluting the River Nile. So we adjure to rescue the River Nile from all kinds of pollution which resulted from the agricultural runoff that carry pesticides and fertilizers, sewage and industrial waste. This can be achieved by the treatment of this water or transporting it to other places for from the river.