الفهرس 
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Abstract
The present study provides a detailed investigation on the seasonal variations of some physicochemical and heavy metals in drainage water in the selected five drains located in Dakahlia Governorate. The main objectives of this study are to characterize and assess of wastewater pollution and to measure the accumulation of heavy metals in gill, liver and muscles of African catfish (Clarias gariepinus) and cichlid fish (Oreocromus niloticus) seasonally during the period of winter 2015 to autumn 2016. In addition, the correlations between water variables heavy metals in water samples with condition factor values of the studied fish species were evaluated.The seasonal variations of the physical and chemical variables of water samples collected from five selected drains at Dakahlia Governorate during winter 2015 to autumn 2016. The physical and chemical parameters were estimated in water samples from each site including: water temperature (oC), hydrogen ion concentration (pH), electrical conductivity (EC), total dissolved salts, dissolved oxygen (DO), biological oxygen demand (BOD), carbonates (CO3), bicarbonates (HCO3), chlorides (Cl), sulphates (SO4), calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), phosphorus (P) and ammonia (NH4). The heavy metal include Pb, Cd, Zn, Co, Cr, Ni, Mn, Fe and Cu in water samples were analysed. It is obvious from the results that, there was a pronounced variations in heavy metal contents in the different water samples, where it showed relative fluctuations among the different study sites and during various seasons. Heavy metal concentrations in water samples collected form the five drain study sites could be ranked as follows: Cu > Ni > Mn > Cd > Co > Pd > Fe > Zn > Cr . Detected as the following order: El-Mansoura > Talkha > Belqas > Aga > El-Manzala Study sites. The seasonal changes in the mean weight, mean length and the condition factor of Clarias gariepinus and Oreochromis niloticus in the selective five study drains were also investigated. The mean weight value of C. gariepinus was 338.68 gm. The mean weight value of O. niloticus attained about 149.91 gm. It is noticed that there was not any O. niloticus fish detected in site 4 during the investigation period. On the other hand, The mean length value of C. gariepinus was 34.08 cm. The mean length value of O. niloticus attained about 19.95 cm. The condition factor (K) of C. gariepinus with the mean value attained about 0.83. The condition factor (K) of O.niloticus attained 1.75.The seasonal changes in the hemoglobin, R.B.Cs., Hematocrit, M.C.V., M.C.H., M.C.H.C., W.B.Cs., alanine aminotransferase (A.L.T.) enzyme and aspartate aminotransfcrnsc (A.S.T.) enzyme of Clarias gariepinus in the five study drain sites were estimated. The hemoglobin content of C. gariepinus attained the mean hemoglobin value of 10.10 g/dl and control sample records 11.67 g/dl. The relationships between the physical and chemical environmental factors, heavy metals, blood picture and condition factor of cichlid fish and clariid catfish at the different study sites were analyzed to distinguish the identified groups. In addition, the application of the canonical corresponding analysis (CCA- biplot) to determine the main environmental factors affecting on the selected fish species, where it was clear that water temperature, magnesium and sulphates showed relatively high significant correlations with the condition factor of the studed fish species with the first and second axes. Dissolved oxygen, sodium, calcium, pH value, potassium, total dissolved salts, biological oxygen demand, chlorides and total dissolved phosphorus exhibited moderate significant correlations. While bicarbonates, electrical conductivity and ammonia exhibited relatively low significant correlations with the first and second diagram axes.