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. Two doses of B. pumilus (106 and 1012 g1 diet fed) and Organic GreenTM (1 and 2 g kg1 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 di¡erential 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 after1, 2 and 8 months using 0.5mL culture suspension of a pathogenic reference strain of Aeromonas hydrophila (108 bacteriamL1). 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 inTLC, 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 di¡erences being statistically signi¢cant in groups 3 and 9. The challenge infection showed a variable responsewiththe type and dose of treatment and the period of application. The highest relative levels of protection were an average increase of 62.5% after 1month (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 e¡ect. 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.