Effects of Selected Probiotics on Water Quality and Growth Performance of Nile Tilapia Cultured in a Recirculating Water System.

This study used selected probiotics (Bacillus subtilis HW3B and Lactiplantibacillus plantarum DW5L) in combination with a recirculating water system to evaluate the effects of the selected probiotics on Nile tilapia growth and water quality in the culture system. The experiment was conducted in aquaria (45 x 60 x 45 cm for each aquarium with 150 liters of water and a 40-liter internal filtration system). Both selected probiotic bacteria were tested in raising 15 fish, 2-3-inch in each Nile tilapia in aquaria with a recirculating water system for 10 weeks by consisting of 4 experimental sets with 5 replications each, consisting of T1 (control set – no microbial products added), T2 (microbial inoculum PM.1, a product of Department of Fisheries as positive control), T3 (mixed selected probiotic strains HW3B and DW5L at 1:1 by volume), and T4 (only B. subtilis HW3B). It was found that T3 significantly controlled BOD and TSS (P < 0.05) better than the control set. T2 was the most effective to control total ammonia, nitrite, nitrate, and total phosphorus, followed by T3, with significant differences. The number of detected bacteria fluctuated with the level of BOD in the water. A significant increase of total bacteria found in T 1 and T4 sets (P < 0.05), while Bacillus spp. found in all inoculated sets (P < 0.05). A remarkable increase of lactic acid bacteria (LAB) was observed only in T3 set (P < 0.05). It can be concluded that the use of T3 (the mixed probiotics HW3B and DW5L set) in combination with the recirculating water system can reduce the amount of waste in the water almost as effectively as the positive control (T2) and significantly better than the control set (T1). Moreover, T3 showed a better tilapia growth performance on final fish body weight and average daily length values compared with the T1 set (P < 0.05).