The effect of the addition of a probiotic mixture of two Bacillus species to a coupled aquaponics system on water quality, growth and digestive enzyme activity of Mozambique tilapia, Oreochromis mossambicus

ABSTRACT The effects of adding a probiotic mixture of Bacillus subtilis and B. licheniformis to an aquaponics system on water quality, fish growth and digestive enzyme activity in Mozambique tilapia, Oreochromis mossambicus, were tested. The fish (36.4 g fish−1 ± 0.10; 3.64 kg m−3 tank volume, 10 fish per tank) were kept in 386-L systems and fed 2% of body mass day−1 for ten weeks. The Bacillus product (Sanolife®PRO-W; 5.0 × 1010 CFU g−1) was added twice weekly. Each treatment was duplicated. The product reduced total dissolved solids and electrical conductivity levels and increased weight gain of Mozambique tilapia. There was no difference between treatment and control in the proximate analysis of the fish. In the Bacillus treatment the activity of the digestive enzymes α-amylase, alkaline protease and alkaline phosphatase was higher than in the control. The probiotic used in this study improved water quality and increased fish growth.