Abstract:
The present research was conducted to determine the effects of different types of commercial probiotics on growth performance, microbial load and immune response of Nile tilapia (Oreochromis niloticus). Seven experimental diets were formulated. Diet1 was the control diet without probiotics while diets 2-7 contained BC 201 (1.3 x 106 CFU/g), BC 201(2.6 x 106 CFU/g), B. licheniformis (1.6 x 106CFU/g), B. licheniformis (3.2 x 106CFU/g), B. licheniformis + B. subtilis (1.28 x 106CFU/g), B. licheniformis + B.subtilis (3.2 x 106CFU/g) respectively. Two hundred and ninety four (294) Oreochromis niloticus juveniles were used for the experiment. The fish were randomly stocked at 14 fish per tank into 21 glass tanks of water representing seven treatments with three replicates per treatment. The fish were fed to apparent satiation twice daily for 56 days. At the end of the experiment, the growth performance, mortality rate, microbial load count and immune responses of Nile tilapia were compared. A challenge test was conducted at the end of the feeding trial using 30 fish from each treatment (10fish/replicates), by introducing 1ml/L of pathogenic bacteria (Salmonella typi) to the fish via oral administration. The mortality rate was estimated for 14days post challenge. Results revealed a marginal increase in the weight gain and Specific growth rate of fish fed dietary probiotics compared with fish fed non probiotics diet. There were significant differences (P < 0.05) in FCR and PER in fish fed different types of probiotics diets in comparison with those of fish fed non-probiotics diets. There was also significant increase (P <.0.05) in the white blood cell counts (WBC) of all the fish fed probiotics diets in relation to fish fed the control diet. In terms of immunity, the group of fish fed probiotics diets showed higher resistance to the pathogenic organisms. It was also observed from the results that fish fed multi-strains of probiotics diets had greater survivability compared to those fed single strain probiotics and the control. The fish fed B. licheniformis + B. subtilis at 3.2 x 106 CFU/g (T7), had the best
survivability ((100%), This study therefore recommends the incorporation of B. licheniformis + B. subtilis (3.2 x 106 CFU/g) to Nile tilapia feed as supplements to stimulate growth, improve microbial balance and immune system.
