Conventional aquaculture systems typically release 70–80% of the N, P and C from feed into the environment, primarily through dissolved and solid wastes, thereby contributing to significant pollution. As an alternative to traditional approaches relying on nitrification followed by water exchange or denitrification, assimilation-based recirculating aquaculture systems (AsRAS )—including aquaponics, algaponics , and bacterioponics —offer a more sustainable solution. All AsRAS couple conventional RAS with an assimilation-based reactor in a symbiotic arrangement, whereby fish-generated wastes serve as nutrients for plants (in aquaponics), algae (in algaponics ), or bacteria (in bacterioponics ) (Zhu et al., 2024; Yogev & Gross, 2019). This configuration enables the biological assimilation of fish waste, which purifies the water for recirculation while simultaneously maximizing water and nutrient use efficiency, minimizing effluent discharge, and recovering or conserving energy.
Over the past few years, we have developed three distinct AsRAS configurations that operate on fresh or brackish water in multi-loop, near-zero waste setups. Each system maintains separate loops for fish production and assimilation-organism growth, optimizing conditions for both products. Our experimental trials demonstrated fish stocking densities as high as 80 kg/m3 (with a typical density of ~50 kg/m3 ), survival rates exceeding 95%, and feed conversion ratios between 1.1 and 1.4. Notable energy savings were observed: over 80% in aquaponic systems and about 50% in biofloc-based RAS. Furthermore, carbon sequestration in aquaponics reached levels 1.4 times higher than the carbon content in feed, achieving a 64% reduction in carbon footprint relative to conventional RAS; greater reductions are anticipated in algaponics -based AsRAS. In all systems, N2O emissions were significantly lower than those from traditional RAS.
These findings are among the first to demonstrate the viability of large-scale AsRAS production with near-zero water and waste discharge, coupled with substantial energy savings. We posit that AsRAS hold considerable promise for replacing traditional nitrification–denitrification-based RAS, thereby advancing more sustainable aquaculture practices.