Abstract
The present study aimed to investigate the effect of different concentrations of protexin probiotic (Enterococcus faecium) on growth performance, differential leucocytes count, phagocytic activity, phagocytic index, serum total protein, albumin, globulin, Total bacterial count, Total enterobacteriaceae count and Total coliform count of intestinal microbial flora of seabass and disease resistance against challenge with Vibrio alginolyticus. Fish were separated in to four experimental groups of 0.0 g/kg feed (control), 0.1 g/kg feed, 0.2 g/kg feed, 0.3 g/kg feed of commercial probiotic protexin concentrate. Fish fed at 3% body weight per day. Results showed that protexin supplementation have significant improvement in growth performance, significantly increasing in lymphocytes, monocytes, phagocytic activity, phagocytic index, Serum total protein and globulin in all treated groups compared to control Contrary neutrophils and albumin/globulin ratio significantly decreased in all treated groups comparing to the control as well as decreasing in Total bacterial count, Total enterobacteriaceae count and Total coliform count of all treated groups comparing to the control. The mortality rates after challenging with Vibrio alginolyticus were significantly lower in all treated groups than the control. Results indicated that by increasing the concentration of the protexin probiotic results getting better in all examined parameters comparing to control. The present study clearly indicated that inclusion of 0.3gm / kg feed of protexin probiotic in fish diet for not less than 6th weeks can improve the immune status of seabass fingerlings to the favor of resistance to diseases.

Key words: Protexin- Enterococcus faecium - sea bass -fingerlings- growth -immune status