الفهرس 
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Abstract
This study was planned as an attempt to throw spotlight on fungal infection among freshwater fish farms in Dakahlia Governorate, this aim was achieved by the following steps: 1-Collection of samples from infected freshwater fishes in different farms during the four seasons of the year. 2-Isolation & identification of pathogenic fungi from infected freshwater fish. 3-Determination of the prevalence of fungal infection among the examined fishes in relation to different localities, fish species and different seasons of the year. In the present study, 500 examined fishes included 300 O.niloticus and 200 C. gariepinus. Fishes were obtained alive from Manzala fish farm and Al-Mansoura private fish farm in Dakahlia Governorate. The fish samples were collected during the period from January 2017 to December 2017. The fungal isolates from infected fishes were Aspergillus flavus, Aspergillus niger,Aspergillus fumigatus, Saprolegnia spp., Penicillium spp., Alternaria spp., Cladosporium spp. and Candida albicans. The prevalence of fungal infection was 29.6% among the examined fishes; the infected fishes were 44.6% from examined O. niloticus and 55.4% from examined C. gariepinus. O. niloticus showed the highest prevalence rate of infection was 12.2%, 6.7%, 6.7%, 5.4%, 5.4% and 4.1% for A. niger, Penicillium spp., Saprolegnia spp., A. flavus, Alternaria spp. and A. fumigatus respectively, while the lowest rate of infection was 2.7 % for C. albicans followed by 1.4% for Cladosporium spp. In case of C.gariepinus showed the highest prevalence rate of infection 14.9%, 9.5%, 8.1%, 6.8% and 5.4 for A. niger, Saprolegnia spp., A. flavus, A. fumigatus and Alternaria spp. respectively, while the lowest prevalence was 4.0% for each of Penicillium spp. and Cladosporium spp. followed by 2.7% for C. albicans. The prevalence of fungal infection showed that, autumn season showed the highest infection rate among examined fishes 41.7%, while spring season was the lowest infection rate among examined fishes 17.5%. The prevalence of fungal isolates from external and internal organs of infected fishes cleared that, skin and fins, gills, liver, kidney, eyes and spleen; the infection rates were 55.4%, 18.9%, 10.8%, 10.2%, 2.7% and 2% respectively. The clinical signs and postmortem (P.M.) lesions findings of infected fishes were reported as: The infected fishes with A.niger showed emaciation with congestion in the internal organs with enlargement of spleen. The infected fishes with A.flavus showed scales loss ulceration of the skin with yellow liver. The infected O. niloticus with Saprolegnia spp. showed cotton-wool like appearance of head region and severe ulceration on the head region. The inflected fishes with Cladosporium spp. and Alternaria spp. showed severe erosions and ulcerations of the skin in the posterior part of the body with black liver. from the results, it can be concluded that, the mycotic infections were illustrated in high prevalence among Nile tilapia (Oreochromis niloticus) and African catfish (Clarias gariepinus) in Dakahlia Governorate during low temperature seasons. The freshwater fishes harboured a number of fungal flora, which are pathogens for fish as Saprolegnia spp., Aspergillus spp., Alternaria spp., Cladosporium spp., Candida albicans and non-pathogenic as Penicillium spp. The isolates of Aspergillus niger, Saprolegnia spp. and Aspergillus flavus were highly prevalence, the isolates of Asperillus fumigatus, Alternaria spp. and Penicillium spp. were moderate prevalence and the isolates of Cladosporium spp. and C. albicans were low prevalence. Clarias gariepinus showed a higher prevalence rate of infection with different fungal species than Oreochromis niloticus.