الفهرس 
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Abstract
Two hundred fish were collected as following : Sixty Tilapia nilotica and sixty Armont catfish were collected from ponds of Faculty of Agriculture (Assiut University ). River Nile and Ibrahimia Canal.
Forty Tilapia mosampikaand forty Channel catfish were collected from ponds of International
Fisheries Academy-United states of America. Fish were examined clinically. (15.15.10.10 fish)
respectively presence of clinical alternations. These fish were subjected to Pill parasitological, and bacteriologically examinations. The clinical alternations were a white line on the alter margin of the fin which progresses toward the base of the fin. As the lesion develops. the alter fin margin
becomes frayed from disintegration of the soft tissues, between the fin. The degenerative process continlles llDtil the whole 1.n is lost and in the case of the caudal fin erosion. only a stump is left. Redness, hemorrhagic patches distributed all over the body and fins, Exophthalmia and anal prolapsed with abdominal distension. Roughness of the scales and their detachment from some parts of the body and formation of ulcers. Parasitological examination of fish revealed the presence of Itch Yophthirisus mu1tifi1is protozoon infestation among the diseased fish which was considered as a stress factor.
Bacteriologic examination of diseased fish revealed the presence of nine isolates from Aeromonas
1iguefacens strains and Four isolate s from Pseudomonas fluoresces strains which were in their morphologic cultural and biochemical behavior closely related to the previous organisms.
The biological properties of the isolates were studied by inoculation in fish. In case of Aeromonaa 1iguefacens strains seven isolate s were found viru1ent, aDd two isolates were avirulent to the tested fish. In case of Pseudomonas fluorescence strains three isolates were found virulent and to the tested fish, one isolate is virulent The infection of fish with Aeromonas liguefacens and
Pseudomonas fluorescence were transmitted experimentally by IIp and lIM routes and not transmitted by scarification of the epidermis. The coldness was essential factor for increasing the incidence of the disease among cultivated fishes. Besides Tilapia, Catfish have been proved to be a good
model for studying the biological properties of fish pathogenic bacteria