Adaptive Biofiltration Strategy for an Evolutionary Relic: Assessing Bacterial Consortia for Nitrogen Management in <i>Huso huso</i> Aquaculture

Recirculating aquaculture systems (RASs) represent a sustainable solution for intensive fish production, offering 90%–99% water savings compared to conventional systems while preventing nutrient contamination of natural waterways. The accumulation of nitrogenous compounds, driven by factors, like overfeeding, fish waste, and insufficient water exchange, can cause major problems in aquaculture production. This study investigated the optimization of biofiltration systems for nitrogen removal in RAS through a factorial design examining two bacterial species ( Nitrosomonas and Nitrobacter ), two substrates (sand and straw), and two cell densities in a beluga ( Huso huso ) sturgeon farm. Results demonstrated distinct functional specialization, with the most effective total ammonia nitrogen (TAN) reduction (upto 85%) achieved by Nitrosomonas in straw and sand systems, while Nitrobacter in straw systems showed 70% nitrite (NO 2 − ) removal. Substrate–microbe interactions were critical, revealing that sand provided an optimal environment for Nitrosomonas , whereas straw optimized Nitrobacter ‐driven nitrite reduction. These findings provide actionable guidelines for designing targeted biofiltration systems in RAS, with sand– Nitrosomonas recommended for ammonia‐dominated systems and straw– Nitrobacter for nitrite mitigation. The study advances sustainable aquaculture practices by demonstrating how substrate‐specific microbial optimization can simultaneously improve water quality management and environmental protection.