الفهرس 
INTRODUCTIONOnly 14 pages are availabe for public view
 |  | from | 204 |  |  |
| | | from | 204 | | |
Abstract
In this study, 200 freshwater Nile tilapia (O. niloticus) weighing 67 ± 12 g were collected seasonally from private fish farms in Ismailia Governorate from May 2018 to March 2019. Bacteriological analysis revealed that 82 out of 200 examined fish were infected with A. hydrophila, F. columnare, and E. tarda with a total prevalence of 41%. Liver, kidney and spleen were the most prominent infected organs with A. hydrophila and E. tarda, while the intensity of F. columnare was confined to the skin lesions and gills. Molecular characterization revealed that all tested isolates of A. hydrophila harbored gyrB aerA and alt genes, while only 6 isolates harbored ahp virulent gene. The developed RPA-LFD assay showed high specificity for F. columnare cslA gene, reflecting its potential use for field detection. All isolates of E. tarda harbored gyrB gene, while only 4 isolates were positive for etfA, etfB, etfD, and etfC. MALDI-TOF MS assay showed remarkable spectral peaks and excellent score values for E. tarda. Dietary supplementation of synbiotic (B. subtilis + β-1,3 glucan) provided significant increases in growth parameters, survival rate, hematological markers (WBCs, RBCs, Hb, HCT%), serum proteins and lysozyme after 45 days of pilot experiment.