الفهرس 
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Abstract
Four hundred and sixteen sarotherodon sp. fish were collected from different pounds of El-Serow fish farm, Menia Governorate. Fish were examined clinically, 165 (39.6%) of them were subjected to P.M. bacteriological and parasitological examinations. The highest percentage of gill affection among examined fishes occurred during summer season (47%) while the lowest one was observed during winter season (30%).
Gill affections among examined fishes occurred during summer season (47%) while the cases from which Flexibacter columnaris have been isolated in summer seacon were 6 (12.7%) with infectivity rate of 6/47, while gill affections among examined sarotherodon S.P. occurred during autumn season (43.2%) with only (14.5%) infected with columnaris disease where the infectivity rate was (7/48).
The clinical alterations observed among infected fish were, sluggish movements, swimming near the surface of the water end rapid swollowing the water mixed With atmospheric air. Infected fish also showed increase breathing frequency while the gill coverings were stretched open widely.
Fish infected with columnaris disease showed noticable congestion of gills with dark reddish discolouration, presence of mucus in the gill puch, loss of scales from the caudal peduncle Vlhich appeared greyish in colour, while the infested with Cichlidogyrus sp. gills showed fading of colour, hypersecretion of mucus on the surface with a cloudy film consisting of slime, In some parts of the
heavily infested gill being expended and very pale causing destruction of the epithelial tissue. In some cases paleness of the gills were alternated with reddish ones but sometimes palness of the gills with greyish descolouration of the free portion and the presence of excessive mucus in the gill pouch. Roughness of the scales and their detatchment.
Bacteriologioal examination of diseased fish yielded thirteen isolates cloely related to Flexibacter columnaris morphologically culturelly and biochemically.
The biological properties of 7 isolates of flexibacter columnaris were studied by artificial inoculation in Sarotherodon sp. fish proved that only three of them (3, 5, 7) were virulent to the inoculated fish with a varying degrees. The isolate No.(3) was found to be highly virulent, while the isolate No.(7) was moderately virulent and the other five isolates .were avirulent to the tested fish.
The antibiogram of Flexibacter columnaris isolates revealed their sensitivity to streptomycin, oxytetracycline and chloramphenicol which could be recommended for in vivo application against their infection. Besides all tested isolated were resistant to bacitracin , a fact which could be recommended for further studies to be used as purifying agent in media used for isolation of Flexibacter columnaris from contaminated samples.
Parasitological examination of fish revealed the presence of Cichlidogyrus sp. a monogentic tremated infestations among the diseased Sarotherodon sp. in one hundredand sixty five fish out of 461, constituting (39.66%) of the examined fish as well as (100%) of diseased cases. The extensiveness of Cichlidogyrus sp. durinp, summer and autumn seasons were 47% and 43.2% respectively while the intensiveness of infeatation was 20-40 and 20-35 parasites/microscopic field respectively. On the
other hand during winter and spring seasons the extensiveness of the parasites was 30% and 38 % respectively and the lntesnsiveness was 2-5 and 5-10 parasites microscopic field respectively. The results showed that Sarotherodon sp. fish reared in Egyptian aquaoulture systems could be infected naturally or experimentally with columnaris disease and also t may contract Cichlidogyrus sp. in a various degrees of severity depending on the variation of temperature and stress factors.