الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 32 |  |  |
| | | from | 32 | | |
Abstract
The occurrence of Edwardsellosis caused by Edwardsella tarda, in cultured freshwater fish, Oreochromis niloticus and Clarias gariepinus in Kafrelsheikh Governorate fish farms was studied, all over the seasons of a year. A total number of 288 fish; 36 / fish species / season, showed gross cutaneous lesions. The examined fish were succumbed for bacteriological isolation, and the isolates were identified through biochemical identification and the suspected isolates were investigated for the characteristics of E.tarda which confirmed by PCR as well as four virulence genes.The seasonal incidence of E. tarda infections was studied in O. niloticus and revealed that the disease and pathogen were recorded only in summer (11.11%) while as, in C. gariepinus the pathogen was isolated allover the seasons, but had the highest incidence in summer (50%) followed by spring (30.55%), autumn (25%) and lastly winter (22.22%).The pathogenicity of the isolated E.tarda strains was evaluated by determination of the lethal dose fifty (LD50) and the experimental infection. The LD50 revealed that, the dilution 105 CFU caused fifty percent mortalities in the fish within (24-48h). The recorded mortalities through the pathogenicity experiments of the four fish groups were higher in groups; one and two infected with E.tarda strains containing four and three virulence genes respectively, whilst the groups three and four, containing two and one virulence genes respectively of E.tarda have a relatively low mortality rates.Some hematological and serum biochemical parameters of the blood and sera of naturally diseased and experimentally infected fish were studied and revealed a decreased Hb, RBCs, PCV, total proteins, albumin and globulins levels and increased TLC and Lysozym concentrations. Histopathological studies on the tissues of naturally diseased and experimentally infected fish were also recorded.