الفهرس 
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Abstract
This study was carried out on 200 catfishes (Clarias gariepinus) collected from farms at Al-Dakahlia governorate from September, 2013 to March, 2014. Fishes were selected on the basis of the characteristic clinical abnormalities. Bacteriological and mycological examinations were carried out under complete aseptic conditions and the affected organs were preserved in formal saline solution for histopathological examination.
Experimental infection was conducted to investigate the effect of Saprolegnia on the percentage of egg hatching and rate of fry survival of the African catfish (Clarias gariepinus).
The results revealed that:
Mycological examination revealed the isolation of 500 fungal isolates (460 molds and 40 yeast isolates). The isolated moulds were classified as follow: Aspergillus flavus (12.0%), Aspergillus niger (34.0%), Aspergillus ochraceus (2.0%), Alternaria Species (6.0%), Cladosporium Species (8.0%), Mucor Species (2.0%), Penicillium Species (4.0%), Scopulariopsis (2%), Fusarium moniliforme (2.0%), Blastomyces (2.0%) Ichthyophonus hoferi (8.0%) and Saprolegnia (10%). Yeast isolates had the following incidence: Candida albicans (6.0%) and Rhodotorula (2.0%). Particular concern was given to monitor the pathologic alterations of these pathogens in gonads of both sexes.
Fungal isolates from different organs of Clarias gariepinus were as follow: Ovary (40.0%), Liver (22.0%), Spleen (14.0%), Kidney (12.0%), Muscles (8.0%) and Testis (4%).
Bacteriogical examination revealed the isolation of 360 bacterial isolates from 200 catfishes belonging to 7 species having the following percentages as follow: photobacterium damselae 30%, Aeromonas hydrophila 20%, Atypical Aeromonas salmonicida 10%, Aeromonas sobria 10%, Vibrio species 25% and 5% for Citrobacter and Salmonella species. These bacteria were isolated from different organs of catfish with the following incidences: Ovary 33%, Liver 22%, Kidney 22%, Spleen 14% and Testis 9%.
The incidence of bacterial isolates from different organs of Clarias gariepinus was as follow: Ovary 33%, Liver 22%, Kidney 22%, Spleen 14% and Testis 9%.
It was concluded that infection with saprolegnia can cause egg mortalities upto 80-100%.
Histopathology revealed the pathologic changes which were associated with the isolated pathogens such as the systemic reactions which varies from leukocytic infiltration in kidneys to granulomatous reaction in the liver. Gonads were of particular concern and ovaries illustrated variable degrees of degeneration and/or regression of ovarian follicles while testes showed necrosis of sperms manufacturing cells. Marked invasion of organs with fungal spores was noticed.