Effect of utilizing a Bacillus sp bacteria consortium for biofilter inoculum in a lab-scale tilapia RAS to enhance...

For the success of recirculating aquaculture systems (RASs), effective biological filtration is essential. This study examined the biofiltration efficiency of four moving bed biofilm reactor (MBBR; abbreviated BF) configurations inoculated with a Bacillus spp. consortium (BC) and their effects on tilapia performance and health. Four treatments were tested: (1) BF₁₂₀BC₀: Biofiltration process lasted 120 days, 60 days before and 60 days during the experiment, without Bacillus spp. consortium addition. (2) BF₆₇BC₆₇: Biofiltration process lasted 67 days;7 before and 60 during the experiment. The MBBR received 1 g BC/m³ media every 15 days. (3) BF₁₂₀BC₆₀: Biofiltration process lasted 120 days, with 60 days without Bacillus spp. Consortium addition before the experiment. Then, the MBBR received 1 g BC/m³ media every 15 days for 60 days. (4) BF₁₂₀BC₆₇: From day 60 to day 7 before the experiment, the MBBR's media was half (2.5 L) and then full (5 L). The MBBR was given 1 g BC/m³ media every 15 days for 67 days, starting from day 7 before the experiment. Using 12 RAS units, 120 tilapia weighing 72.41 g were stocked at 10 fish per tank, totaling 12 kg/m³, in four groups of three replicates. The first month's water exchange was 1%, the second 2%. The results showed that adding Bacillus spp. consortium to the longer MBBR configuration period improved water quality, fish performance, and tilapia health. Compared with the other treatments, the BF₁₂₀BC₆₀ treatment showed enhanced performance in tilapia growth, feed utilization, and body composition. It also had a significant (P ≤ 0.05) effect on serum digestive enzymes, lipid profiles, liver and kidney enzymes, immunity, stress levels, antioxidants, immune/growth-related hormones, and health indicators in the gills, intestines, and liver.