The Nile tilapia ( Oreochromis niloticus) is one of the most popular species worldwide. Nevertheless, intensive aquaculture systems is the most common fish farming systems generate a high amount of ammonia, a major metabolic waste product of fish, owing to fish waste and feed residue decomposition, increased organic matter deposition at the bottom of ponds, and a shortage of dissolved oxygen. On the other hand, plant extracts Yucca schidigera has been proven to be a potent, cost-effective agent for controlling ammonia. The inclusion of dietary Bacillus subtilis stimulates the immune system, promotes growth performance, and modifies the intestinal flora. Thus, evaluating the effect of using yucca and/or Bacillus bacteria on growth performance, immune status, and water quality of cultured Nile tilapia is the main objective of the current study.
As for the un-ionized ammonia (NH3 ), CON gave a significantly higher value than the rest of the treatments; YB yields the lowest value of all. The highest growth performance and feed utilization were observed in the B treatment, followed by the YB treatment, while the control and Y treatments gave lower results. PA ; PO; RB and ACH50 were showed the highest levels for YB-treatment with significant differ ences from the rest treatments; the lowest level was obtained for control (Table 2) . LSZ lowest value was reported for YB-treatment which differs significantly from other treatments; the lowest value was for the control. The highest activity of SOD, GPx and GH were observed for YB- treatment, while the lowest activity was for the control (Table 1) . Control showed the highest MDA result while the lowest result was reported for YB-treatment. The highest activity of Il-8 and Il-1 cytokines activity were observed for B- treatment followed by YB- treatment and control which possess the lowest activity. YB-treatment gave the maximum mean value of Tnf cytokine followed by B-treatment which higher than Y-treatment and control (Table 3).