Firstly, current status of RAS (recirculation aquaculture systems) sector especially in the Baltic Sea region but also in the global perspective is reviewed. Of the Baltic Sea countries, Denmark has been the pioneer of RAS farming and is also a strong player as a RAS technology developer and supplier. Denmark has invested in RAS farming R&D and the regulation includes incentives to adopt discharge abatement technologies.
In the second part, nutrient abatement technologies and typical nutrient discharges are presented and an overview of various RAS technologies is given. Depending on technological details, phosphorus and nitrogen discharges can be reduced by appr. 80-90 % in comparison to cage aquaculture. However, carbon footprint of RAS farming is much larger than in cage farming especially due to high electricity consumption of the RAS processes.
In the third part, RAS cost items are presented, whereafter both literature feasibility studies and RAS company accounting data are used in the economic analysis for discussion what can be considered as BAT in the Baltic Sea aquaculture. Based on the available data, the economic performance of RAS companies is much poorer than estimated in feasibility studies, where preconditions for RAS projects have been evaluated. Despite public subsidies for the investments, RAS farms are mostly heavily on red and several companies have terminated their activities or are bankrupt. Although large RAS projects are still being launched especially for Atlantic salmon smolt production but also to grow larger fish, it is questionable to argue that RAS farming is the best available technology for market size rainbow trout farming in the Baltic Sea countries.