Mortality of fish challenged with A. hydrophila was decreased in all mistletoe-treated group. Abd El-Rhman [52] reported that crude propolis and its ethanolic-extract reduced A. hydrophila induced mortality, indicating the positive effect of the propolis extract in activating the immune system of the tilapia. Similar reports regarding the reduced mortalities on challenge with A. hydrophila were presented [53-56]. In the present data, 50 mg mistletoe-treated group C showed the highest survival rate compared to control. The challenging test suggests that dietary supplementation of an appropriate concentration of mistletoe extract has enhancing effects on disease resistance of tilapia.