الفهرس 
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Abstract
The present investigation deals with a study on the helminth parasites of brackish water fish collected from Lake Burullus. Particular emphasis is laid on certain aspects of the host specificity, effect of host length on the incidence of the parasites. 740 Fish were collected from Lake Burullus, belonging to six families, six genera and six species. The fish were 200 Clarias gariepinus, 250 Oreochromis niloticus , 80 Dicentrarchus labrax, 50 Anguilla anguilla, 60 Cyprinus carpio and 100 Mugil cephalus. The incidence of infection among the examined fish was 203 fishes (27.4%). The majority of the infected fish harbour only single helminth infection (Trematodes) was recorded Dicentrarhus labrax and Mugil cephalus, while Oreochromis niloticus has double helminth infections (Trematodes and Acanthocephala) whereas, Clarias gariepinus have triple helminth infections, (Trematodes, Cestodes and Nematodes). On the other hand, two species of fish have no helminth infections viz, Anguilla anguilla and Cyprinus carpio. The great majority of incidence of infection (29.5%) are due to cestodes and nematodes, while the incidence of trematode infections is (26.1%), while the incidence of acanthocephalan infection is very low (14.7%). The incidence of various trematode genera in different species of fish are 9.8% for both Astiotrema and Orientoreadium, Acanthostomum 3.9% and Pseudopecoelina 2.4% . On contrary cestode infection genera are 23.1% for Polyonchobothrium and 6.4% for Monobothroides then for nematode infection genera 29.5% recorded and finally 14.7% recorded for Acantrocephalan infection. The last chapter of the thesis faithful to a detailed morphological and taxonomic study on four species of trematodes, two species of cestodes and one species for nematodes and acanthocephalan. These species are described and compared with other studies in different locations. There are single genus of trematode infection; Pseudopcaelina is recorded for the first in such locality Lake Burullus. This study deals with ultrastructural study of scolex, spermiogenesis and spermatozoon of the Polyonchobothrium clarias (Cestode: Pseudophyllidea) an intestinal parasites of the Clarias gariepinus.