Effect of synbiotics between Bacillus licheniformis and yeast extract on growth, hematological and biochemical indices of the Nile tilapia (Oreochromis niloticus)

Twelve practical diets were formulated to contain four levels of Bacillus licheniformis (0.0, 0.24 × 106, 0.48 × 106 and 0.96 × 106 CFU g−1), respectively, with three yeast extract levels (0%, 0.5% and 1%), respectively. Each diet was randomly assigned to duplicate groups of 50 Nile tilapia (Oreochromis niloticus) (5.99 ± 0.03 g) in 24 concrete ponds (0.5 m3 and 1.25 m depth) for 12 weeks. Increasing dietary B. licheniformis levels in O. niloticus and yeast extract levels significantly (P < 0.01) improved growth performance and nutrient utilization. Supplementation of the experimental diets with, 0.48 × 106 CFU/g−1 and 1.0% yeast extract showed the best nutrient utilization compared to other treatments. All probiotic levels significantly (P < 0.01) increased chemical composition (P < 0.05) compared to the control group, while increasing yeast extract did not significantly alter chemical composition. Hematological indices, total protein and albumin of O. niloticus significantly increased while aspartate aminotransferase and alanine aminotransferase significantly (P < 0.01) decreased with an increase in B. licheniformis level up to 0.48 × 106 CFU g−1. Increasing levels of yeast extract had no effect on hematological parameters and the diets supplemented with 0.48 × 106 CFU g−1 and 0.5% yeast extract showed the highest hematological values.