Effect of probiotics on the survival, growth and challenge infection in Tilapia nilotica (Oreochromis niloticus)

This study was conducted in order to evaluate the potential bene¢t of Bacillus pumilus and a commercial product (‘Organic Green’ TM ) as a probiotic in the culture of the tilapia nilotica .T wo doses ofB. pumilus (10 6 and 10 12 g � 1 diet fed) and Organic Green TM (1 and 2 g kg � 1 diet fed) were used as feed additives and administered for periods of 1 (groups 2, 3, 4 and 5 respectively) and 2 (groups 6, 7, 8 and 9 respectively) months; group 1 served as a control. Each group consisted of 4 equal replicates of 320 ¢sh. Body weight, nitroblue tetrazolium (NBT) activity, haematocrit values and total and diierential leucocytic counts (TLC and DLC) were recorded in each group after 1 and 2 months. At the end of the experiment (8 months), survival and individual body weights were recorded. Challenge infections were performed after 1, 2 and 8 months using 0.5 mL culture suspension of a pathogenic reference strain of Aeromonas hydrophila (10 8 bacteria mL � 1 ). The NBT values were increased signi¢cantly in all treated groups, except those administered B. pumillus (groups 3 and 6). There were signi¢cant changes in haematocrit values and TLC and DLCs in the treated groups, except group 3, which showed a signi¢cant increase in TLC, lymphocytes and monocytes. There was a statistically signi¢cant increase in the individual body weight in groups 5, 6, 8 and 9. The survival rates of all treatment groups were higher than the control group, the diierences being statistically signi¢cant in groups 3 and 9. The challenge infection showed a variable response with the type and dose of treatment and the period of application. The highest relative levels of protection were an average increase of 62.5% after 1 month (groups 3 and 5), 55.6% after 2 months (group 7) and 15.8% after 8 months (groups 8 and 9). Overall, both types of probiotics induced a similar eiect. The results show the potential of using probiotics to enhance immune and health status and improve disease resistance in Oreochromis niloticus, thereby improving growth performance. However, further extensive testing, including a full commercial cost^bene¢t analysis, is necessary before recommending their application in aquaculture.