Fish welfare and performance in recirculating aquaculture systems

Recirculating aquaculture systems (RAS), in which fish tank water is recycled with the aid of biological filters, is little used in Norway. RAS may offer advantages over traditional flow-through (FT) systems, regarding sustainability and fish welfare, but these aspects have been little studied for Atlantic salmon smolt production. The main hypothesized advantages concern reduced use of water for production, improved control and stability of environmental conditions for the fish, and fulfillment of strict waste discharge limits. However, welfare and performance of Atlantic salmon in such production systems must be secured. The competence of the Norwegian aquaculture research sector is low in this field, a situation that must be remedied. AKVAFORSK has reco gnized these limitations, and made a strategic decision to improve the competence regarding RAS. In RASALMO, the overall aim is to improve the knowledge of how welfare and performance of Atlantic salmon relate to environmental conditions in RAS. In the first section we will investigate effects of fish density, ammonia, nitrite, and temperature, parameters that have not been sufficiently studied regarding RAS and Atlantic salmon. In the second part, focus will be put on RAS design and water quality manag ement, including a long-term comparison between FT and RAS, tank hydraulic parameters, and strategies to maintain fish welfare around milestones such as vaccination. Finally, feed pellet structural stability will be investigated, issues affecting mechanic al filtration and thus biofilter function. A limited study of microorganism classes in RAS will be performed on selected trials. To complement traditional parameters, development of sensitive indicators of fish welfare and performance will be conducted, s uch as molecular and biochemical markers. The project will be lead by a group of scientists with knowledge of welfare, physiology, and molecular biology, as well as microbiology and RAS design.