Abstract
A total of 100 fish samples (Oreochromis niloticus) were collected as 25 fish apparently health and 75 fish appeared to be clinically diseased fish. Samples of kidney, heart, liver, gills and skin lesions are collected and cultured on TCBS medium. Eighty three samples show biochemically positive to vibrio species.10 random samples amplified to 16srRNA gene by PCR technique for more accurate identification resulting in 8 isolates were positive to 16srRNA.The 8 isolates amplified to suspected species specific primers. Resulted in 4 V.parahaemolyticus (50%), 2 V. harveyi (25%) ,1 V. anguillarum (12.5%) and 1 V. alginolyticus (12.5%). Each species amplified to PCR technique for more identification to virulence genes. V.parahaemolyticus amplified to tdh and trh; V. harveyi to Partial hly and Vhh; V. alginolyticus amplified to trh and tdh and V.anguillarum amplified to virA and angM. This study proved that PCR protocols could be useful tools for rapid and simultaneous detection of different Vibrio species virulence factors. Also using of 16srRNA gene in molecular characterization (PCR) of Vibrio is the fastest and most accurate method to identify all isolates of Vibrio.

Key words: Vibriosis, vibrio species, PCR, 16srRNA and Virulence factors.