الفهرس 
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Abstract
The present work provides mainly studying the relationship between the ecological characteristics of water, hematological and parasitological features of the most common monogenean, Cichlidogyrus halli parasite species infesting the cichlid fish Oreochromis niloticus on each host inhabiting three sites in the same Nile Delta region. The study sites were located at Dakahlyia Governorate, Sherbin, Kafr El-Dabosy village namely, Damietta branch of the River Nile, Drain no.1 (Parallel to Damietta branch of the River Nile at this area) and Pumping Station (Connecting canal with pumping station between the other two study sites) were selected for the water and host collection samples. A total of 36 water samples were collected monthly and 600 specimens of the cichlid fish, Oreochromis niloticus Linnaeus 1757 were collected seasonally between winter 2016 to autumn 2017. The monthly fluctuations of the physical environmental factors of water from Damietta branch of River Nile, Drain No.1 and Pumping Station. The following abiotic parameters were estimated in each water sample: water temperature (°C), hydrogen ion concentration (pH), electrical conductivity (EC), dissolved oxygen (DO) and biological oxygen demand (BOD). Also five heavy metals: Iron (Fe), chromium (Cr), Zinc (Zn), Lead (Pb) and Magnesium (Mg) were measured. According to chemical parameters, there is a remarkable increase in mean K+ in PS (5.81 mg/l) with a notice high values (169.83, 6.51, 27.73, 27.73, 87.13, 52.92, 611.04, 303.52 mg/l) of mean Na+, Mg+2, Ca+2, Cl-, HCO3-, TDS and SO4+2, respectively, in D1 comparing to corresponding values in PS and RN. On the other hand, there is a remarkable decrease in mean Na+, Cl-, TDS, SO4+2 and N in PS (43.09, 23.09, 188.25, 85.05 and 6.76 mg/l, respectively) with a remarkable decrease in Mg+2 (1.08 mg/l) during winter in RN. Statistically, One-way ANOVA test revealed that there was very high significant difference of K+, Na+, Ca+2, Cl-, HCO3-, TDS and SO4+2 between different study sites (p ≤ 0.001). On the other hand, One-way ANOVA test revealed that there was high significant difference of Mg+2, N and P between different study sites (p ≤ 0.01). The Canonical Correspondence Analysis (CCA) program analyzes the input data of all water variables (physical and chemical parameters) for each site monthly then detects the degree of different correlation between each blood analysis variable with the prevalence of parasites. According to prevalence of parasites, all physical and chemical water parameters showed high significant effect on prevalence of parasites in fish under investigation at the first and second axes. In addition temperature showed to more affective in spring and summer seasons, HCO3 in autumn and Cl, EC, SO4, Na, K, Ca, Mg and DO showed to be more affective in winter season. Also the appearance of all three study sites in near the center indicated that these results were similar for the three study sites.