الفهرس 
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Abstract
This work was carried out on a total number of 835; including 348 (wild and cultured) Nile tilapia (Oreochromis niloticus), 219 African catfish (Clarias gariepinus), 79 Stripped grey mullet (Mugil cephalus), 76 Nile Perch (Lates niloticus) and 41 Grass Carp Ctenopharyngodon idella which were collected during period from February to November (2013) from different localities of El – Riah El- Tawfiki and Its tributaries and fish farms in Kafr Elshikh. This study showed that the prevalence of internal parasitic diseases in some fresh water fishes at different seasons and the molecular identification of Contracaecum species which were isolated from Lates niloticus and Oreochromis niloticus. The examined fish were subjected to Clinical, postmortem and parasitological examination. The gross appearance of most infested fish species with internal parasitic diseases showed no pathognomonic clinical signs or abnormalities except slight abdominal distention. Postmortem examination of such fish revealed presence of white nodules with varied size attached to the lateral musculature, eye and internal organs including kidneys, spleen, intestine, liver and heart. Others infested with internal parasites showed emaciation, intestinal wall was congested with the presence of ulcer and protruded anal opening, enlargement liver with distended gall bladder. Wet, squash preparation and stained slides were used for isolation and identification of internal parasites. The isolated parasites include: 1- Myxosporidia spores which infested wild O. niloticus was found as macroscopic nodules, creamy whitish cyst, oval in shape and its number varied about 5-8 cysts per fish that found at the base of gill arch, inner surface of operculum, kidneys and eyes around irris. The total prevalence of Myxosporidia species in wild O. niloticus was (24%) with seasonal prevalence of 28.3, 8.0, 16.4 and 43.3% in spring, summer, autumn and winter, respectively. 2-Henneguya species which were isolated from C. gariepinus appeared as many oval to round nodules which attached to the dentritic organ and intestine. These nodules appeared yellowish in color, filled with milky fluid white in color containing a suspension of mature spores. The total prevalence of Henneguya species was (43.65) with seasonal prevalence of 50.6, 30.8, 37.1and 56.1%in spring, summer, autumn and winter, respectively. 3-Henneguyia species which were isolated from Lates niloticus liver and intestinal wall where appeared as nodules of varied sizes. These nodules were yellowish white in color, filled with milky white fluid containing a suspension of mature spores. The total prevalence of Henneguya species was (57.9) with seasonal prevalence of 69.2, 30.0, 60.9 and 71.4 %in spring, summer, autumn and winter, respectively. 4-Myxosporidia spores which were obtained from Mugil cephalus characterized by presence of white nodules embedded in the mesenteries. The total prevalence of Myxosporidia spores was (65.2%) with seasonal prevalence of 80, 37.1, 58.5 and 85 %in spring, summer, autumn and winter, respectively. 5-Myxosporidia spores which collected from grass carp gill filaments and embedded in kidneys tissues appeared as pin point yellowish white cysts. The total prevalence of Myxosporidia species was (47.2%) with seasonal prevalence of 63.6, 20.0, 38.5 and 66.7 %in spring, summer, autumn and winter, respectively. Along the period of study, cultured O. niloticus was not showed Myxosporidiosis. 6- Encysted metacercariosis in O. niloticus was represented in both of Clinostomum tilapiae and Euclinostomum tilapiae where clinostomum tilapiae appear as yellowish white to orange pea- like cyst measuring 1.5 to 3.5 mm. They were arranged in groups and appear as grape like structure which embedded in the branchiostegal musculature with seasonal prevalence of 6.6, 27.7, 14.5 and 0 % in spring, summer, autumn and winter, respectively, while Euclinostomum tilapiae were embedded in the tissues of the anterior and posterior kidney of O. niloticus. The cysts are of variable size (2-4 mm) with thin wall. They appear as round to oval greyish black cysts with seasonal prevalence of 20.0, 27.3, 19.3 and 6.7 % in spring, summer, autumn and winter, respectively. The metacercariosis infestation of wild catfish appeared as nodules of varied sizes and reaching to hundreds in number in heavily infested cases which mainly found in musculature, liver, spleen, stomach, intestine, kidneys and heart with seasonal prevalence of 58.8, 48.7, 62.9 and 17.1 % in spring, summer, autumn and winter, respectively. Along the period of study, neither Lates niloticus nor Mugil cephalus nor Ctenopharyngodon idella were infested with metacercariosis. 7- Concerning the intestinal helminthes in O. niloticus and C. gariepinus; Acanthocephalans parasites were collected from the intestines O. niloticus and C. garipinus. Nematodes as procamallanus laeviconchus and paracamallanus cyathopharynx were recovered from stomach and intestine of C. garipinus. Polyonchobothrium clarias was the only cestode which was recovered from stomach and intestine of C. gariepinus. The highest rate of the intestinal helminthes was at spring followed by summer then autumn and winter. Contracaecum spp was isolated from the abdominal or pericardial cavity of O. niloticus and Lates niloticus with highest prevalence at summer season reach 90%. The PCR amplification of DNA which was obtained from contracaecum species showed that there was difference in PCR products. In O. niloticus, the PCR amplification performed using universal primers for family Anisakidae (NC2 r and NC5 f) produced band at 150 bp. In Lates niloticus, the PCR amplification performed using universal primers for family Anisakidae (NC2 r and NC5 f) produced band at 100 bp.