Probiotic microbial feed supplements are gaining wide acceptance in livestock production, and may be applicable to aquaculture production systems. The present study was designed to investigate the effect of incorporation of probiotics
(Bacillus subtilis and Biogen®), spices (garlic or fennel) and also a combination of B. subtilis with garlic or fennel in the diets of Nile tilapia, Oreochromis niloticus.A total of 420 Nile tilapia fry were divided into seven treatments (3 replicates for each treatment) and fed on the experimental diets for 90 days. The basal diet was fomulated to contain 30% CP and 2700 Kcal ME kg-1 and divided into 7 diets. The 1st one as a control diet (D1). The other diets were supplied by the diffeent additives, B. subtilis (D2), 0.2% Biogen® (D3), 1% garlic (D4), 1% fennel (D5),B. subtilis+1% garlic (D6) and B. subtilis+ 1%fennel (D7).Results of the present experiment indicated that, supplementation of the basal diets with probiotics B. subtilis or Biogen® and spices (garlic or fennel)significantly (P<0.01) improved survival rate of Nile tilapia. A combination of B. subtilis and garlic or fennel showed the best fish survival rate but did not significantly differ from those recorded for the diets supplemented with probiotic or spices alone.Feed intake (FI), feed utilization and growth performance of Nile tilapia including final body weight (BW), final body length (BL), weight gain (WG),
specific growth rate (SGR), feed conversion ratio (FCR) and protein efficiency ratio (PER), were significantly (P<0.01) higher in all treatments than the control diet. The combination of B. subtilis and fennel in tilapia diets showed the best
feed utilization (FCR and PER) and the highest growth performance (BW, BL,WG, and SGR) compared to the other treatments.The highest and optimum feeding behaviour among treatments was observed in fish fed on the diet D7, while the lowest feeding behaviour was recorded in fish fed on the control diet (D1). Moreover, the combination of B. subtilis with garlic or fennel improved the feeding behaviour than that observed in fish fed on the diet supplemented with B. subtilis alone. There was no significant difference in agonistic activities amongst fish fed on the different diets supplemented with probiotics or spices and the control diet. Probiotics (B. subtilis or Biogen®) or spices (garlic or fennel) or the combinations of B. subtilis and garlic or fennel in the diets of Nile tilapia significantly (P<0.01) decreased hematocrite (Ht) and reduced the levels of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) while hemoglobin (Hb) showed some variation (but not significant). Dry matter (DM), crude protein(CP) and ether extract (EE) of fish whole-body were significantly (P<0.05) affected by the different treatments compared to control fish group.