A 90-day experiment was conducted to evaluate the effects of the addition of a probiotic mixture of Bacillus subtilis and B. licheniformis to a coupled aquaponic system on growth and composition of gastrointestinal microbiota of juvenile Mozambique tilapia, Oreochromis mossambicus . A total of 96 fingerlings (4.74 ± 0.01 g fish−1 ) were randomly distributed into replicated independent aquaponic systems, with each containing 24 fish. Aquaponic systems assigned to the Bacillus treatment received 5.31 g of a commercial Bacillus mixture (Sanolife®PRO-W; 5.0 × 1010 CFU g−1 ) twice weekly until the end of the experiment. The addition of the probiotic resulted in increased weight gain, specific growth rate, feed efficiency and improved feed conversion ratio. Water quality remained within recommended ranges for tilapia culture, while free ammonia levels were reduced in the treatment systems. Microbial characterisation by Illumina MiSeq sequencing of 16S rRNA gene amplicons showed that bacterial gut communities were dominated by the phylum Fusobacteria, specifically the species Cetobacterium somerae . Compared to the control, lower relative abundances of members of the family Enterobacteriaceae , represented by genera Aeromonas , Edwardsiella , and Klebsiella were observed in the gut of O. mossambicus from the Bacillus treatment. The Shannon index values significantly decreased in the Bacillus treatment as compared with control, which suggests that the bacterial community was not modified to a large extent by the addition of Bacillus spp. This study establishes baseline data for probiotic trials in aquaponic systems.
KEYWORDS Bacterial communities, probiotics, Next-generation sequencing