Aquaculture plays a crucial role in meeting the escalating global demand for animal protein. However, some aquaculture systems are often linked to high rates of greenhouse gas (GHG) emissions. A promising alternative to minimize emissions is the adoption of recirculating aquaculture system (RAS), an emerging practice in the aquaculture industry that intensifies production while reducing water and land use. Yet the effects of RAS on GHG emissions remain poorly understood. We demonstrate that most emissions from a RAS-based Nile tilapia fish farm with suspended tanks originate from the water treatment system (biofilter), and that the total CO2eq emission is lower than that of other animal protein sources.
After calculating the daily fluxes of CH4 and CO2, we observed that the CH4 flux increased considerably in the biofilter as the production cycle progressed, while the CO2 flux decreased due to the primary production by Lemna minor and Pistia stratiotes L. Additionally, we observed a higher ebullitive emission than diffusive emission from the RAS, and a difference between measurements with the aerator on and off in the tanks. We found a total of 2.97 tons of CO2eq directly emitted by the RAS-based fish farm and 2.03 kg CO2eq/kg protein or 0.32 kg CO2eq/kg live weight. The biofilter accounts for ~98% of the emissions and the total emissions per protein is mostly the result of indirect emissions. Our results highlight the need to seek further improvements in RAS, to reduce emissions particularly from water treatment systems to further decrease emissions per protein production in aquaculture.