الفهرس 
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Abstract
Fish parasites and diseases constitute one of the most important problem confronting the fishery biologists. The parasites mainly affect the marketability of produced fish. Although there have been considerable literatures recorded the presence of helminths in many fish in and outside Egypt, but only little of them focus on biological factors affect the presence of the parasites infecting fish. Hence our research studied the occurrence of helminths in some commercially important fish found in Port Said markets and they were hunted from Lake Manzala with studying the effect of biological factors represented by sex lengh and weight of the host on the rat of parasitic infection. Genetic techniques were used to study the similarities and differences between some of these helminths.
In our research 30 samples of T. nilotica 30 samples of T.zilli and 30 samples of C gariepinus were collected from Port Said markets (Lake Manzala ) The sex, weight and lenghth of the collected samples were determined The samples were examined to detect the infections with different helminths The relation between some biological factors and the occurrence of infection representing in prevalence intensity and abundance of infection was studied The diploid chromosome numbers and karyotype of some isolated helminths were determined The phylogenetic differences among the helminths and the phylogenetic relationship among helminths using polymerase chain reaction (PCR) RAPD using ten primers (10 nucleotides )was also recorded
In T. nilotica the recovered helminths were the metacercariae of centrocestus sp Haplorchis sp Stictodora sp pygidiopsis sp. Echinostoma sp and undifferentiated metacercariare The total mean prevalence of infection was (86.7%) the total mean abundance of infection was (1527.3+-461.1) and the total mean intensity of infection was (1762.3+-517.6) and the highest prevalence was recorded in stomach. The highest prevalence was recorded for undifferentiated metacercariae followed by Centrocestus sp The host length weight and sex affect the prevalence of helminths the highest values were recorded in larger fish and in males and the total mean abundance and intensity of infection were directly proportional to prevalence.
In conclusion the incidence of parasitic infections recorded in the present study was markedly high and showed different responses to the biological factors that varied according to parasite species and fish host. Further investigations are needed regarding the quality and marketability of fish from Lake Manzala. In addition the present study confirms that RAPD-PCR is a useful technique to estimate the genetic variability and degree of similarity among helminths species . Fish parasites and diseases constitute one of the most important problem confronting the fishery biologists. The parasites mainly affect the marketability of produced fish. Although there have been considerable literatures recorded the presence of helminths in many fish in and outside Egypt, but only little of them focus on biological factors affect the presence of the parasites infecting fish. Hence our research studied the occurrence of helminths in some commercially important fish found in Port Said markets and they were hunted from Lake Manzala with studying the effect of biological factors represented by sex lengh and weight of the host on the rat of parasitic infection. Genetic techniques were used to study the similarities and differences between some of these helminths.
In our research 30 samples of T. nilotica 30 samples of T.zilli and 30 samples of C gariepinus were collected from Port Said markets (Lake Manzala ) The sex, weight and lenghth of the collected samples were determined The samples were examined to detect the infections with different helminths The relation between some biological factors and the occurrence of infection representing in prevalence intensity and abundance of infection was studied The diploid chromosome numbers and karyotype of some isolated helminths were determined The phylogenetic differences among the helminths and the phylogenetic relationship among helminths using polymerase chain reaction (PCR) RAPD using ten primers (10 nucleotides )was also recorded
In T. nilotica the recovered helminths were the metacercariae of centrocestus sp Haplorchis sp Stictodora sp pygidiopsis sp. Echinostoma sp and undifferentiated metacercariare The total mean prevalence of infection was (86.7%) the total mean abundance of infection was (1527.3+-461.1) and the total mean intensity of infection was (1762.3+-517.6) and the highest prevalence was recorded in stomach. The highest prevalence was recorded for undifferentiated metacercariae followed by Centrocestus sp The host length weight and sex affect the prevalence of helminths the highest values were recorded in larger fish and in males and the total mean abundance and intensity of infection were directly proportional to prevalence.
In conclusion the incidence of parasitic infections recorded in the present study was markedly high and showed different responses to the biological factors that varied according to parasite species and fish host. Further investigations are needed regarding the quality and marketability of fish from Lake Manzala. In addition the present study confirms that RAPD-PCR is a useful technique to estimate the genetic variability and degree of similarity among helminths species .