Integrated biofloc-based tilapia aquaculture system with mussels enhances growth performance and functional potential for nitrogen removal.

Aquaculture produces more than half of the global fish supply, providing high-quality protein for humans. Biofloc technology improves feed nitrogen utilization efficiency through microbial protein recycling, which is crucial for increasing fish production and reducing environmental impact. However, the poor palatability of microbial flocs and excessive biofloc accumulation can limit nitrogen recovery and the sustainability of traditional biofloc aquaculture (BAT). Here, we developed a novel pilot-scale biofloc-mussel aquaculture system (BMAT) to enhance nitrogen recovery and compared its performance with BAT. Batch experiments showed that a biofloc concentration of 0.4 g L-1 provided a balanced condition for biofloc biomass growth (14.3 mg L-1 d-1) and high TN removal efficiency (93.2 %). Long-term culture experiments demonstrated that BMAT increased the specific growth rate (SGR) of tilapia (Oreochromis sp.) by 14.1 % and fish nitrogen recovery by 5.7 %. qPCR showed significantly higher TSS-normalized abundances of nitrification-related (AOA-amoA and AOB-amoA), denitrification-related (nirK and nirS), and N2O-reduction-related (nosZI) genes in BMAT. Overall, BMAT provides a promising micro-ecological approach that enhances fish growth with numerically higher nitrogen recovery and greater genetic potential for N2O reduction per unit biofloc biomass under pilot-scale conditions.