الفهرس 
Relaxation and fixationOnly 14 pages are availabe for public view
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Abstract
The most common fresh water fishes in Gharbia governrate, that peoples like to eat are, Clarias lazera, Bagm bayad and Oreochromis niloticus. So the present research dealed with a surrvielence study of parasites infecting fresh water fishes and the effect of ecological factors as well as mollusccides on the prevalence of infection. Collection of fishes was carried out from Demietta branch in Zefta for a year period ( June 1994 till June 1995). In addition another samples were collected from fish markets of Tanta City. More than 485 fish specimens were collected; 335 specimens belonging to Clarias Zazera., 90 Bagrus bayad and 60 Oreochromis niloticus. Surrveiknce study : 1- The parasites collected fkom these fishes are 20 species belonging to 3 phyla, 12 families and 14 genra . (Table 33) 2- The Monogenea constitute seven species, digenetic trematodes nine species, cestode one species, nematodes two species and copepodes one species. 3. Astiotrerna diverticuli n.sp. (Trematoda : Plagiorchiidae) recorded as a new species from the intestine of Clarias lazera. This species is characterized by the presence of two oesophogeal flaps open into the intestinal caeca by a constriction which may act as a valve that controlling passage of food to these caeca. 4- Cotylaspis sp. ( Aspidogastrea : Aspidogastridae) from the intestine of Clarias lazera and Lamproglena rnonodi from the gills of Oreochrornis niloticus are new records of the Egyptian fauna. 5- Scanning electron microscope was used to study the fine structure of some species and add fine diagnostic characters for some species. 1- It was found that the increase of the length of the host results is in an increase in the prevalence of infection. 2--The prevalence of infection in females is higher than in males. 3- The prevalence of infection reaches its peak in the spring and summer while they are approximately zero in winter. 4- from the experimental study on the effect of temperature on the ectoparasites, it was found that these parasites can live in a wide range of temperatures from 10-32OC while below 10•‹C or above 32OC they begin to die. 5- The study of the effect of 10 mg./L. copper sulphate ( as a molluscide) revealed that, this cencentration is effective to kill ectoparasitic Monogenea after five hours. This study was confied by using scanning electron microsocpe to investigate the effect of CuSo, on the monogenean parasites.