Recirculating aquaculture systems and fish welfare: A critical overview of constraints and opportunities

Recirculating Aquaculture Systems (RAS) represent a transformative approach to fish farming, offering a controlled and sustainable alternative to traditional open systems. While RAS offer significant opportunities for improving fish welfare, they also introduce unique challenges that must be carefully managed to ensure optimal health and welfare of cultured species.
From a fish welfare point of view, an advantage of RAS is the ability to maintain stable and customizable water quality parameters, which allows for the creation of species-specific environments that can reduce stress and disease susceptibility. Furthermore, the biosecurity inherent to closed systems minimizes the risk of pathogen and parasite exposure and facilitates early detection and intervention in case of health issues. These features collectively contribute to improved survival rates, growth performance, and overall welfare outcomes. Despite these benefits, RAS systems also pose several welfare-related challenges. Energy-related costs inherent to RAS often require relatively high stocking densities to optimize production efficiency; stocking density and other management-related procedures need to be considered carefully to avoid deleterious effects on fish welfare. Water recirculation induces alterations on water physicochemical and microbiological variables that are relevant to fish, some well-known but several also less known, and more research is needed to better characterize welfare affecting parameters in RAS. In addition, relevant knowledge gaps remain about potential effects of RAS design-related variables on the welfare of different fish species.
Opportunities for enhancing welfare in RAS include the integration of precision aquaculture tools, such as automated monitoring systems (involving AI, machine-learning, etc.) for both fish and system performance as well as behavioral analytics, which can provide real-time insights into fish condition and environmental parameters. Additionally, research into species-specific preferences and behavioral needs should contribute to the design of more welfare-friendly RAS environments. Research and innovations on RAS-specific feed formulations, development of fish strains specifically adapted to RAS, optimized lighting regimes and rearing unit design, and co-rearing with low-trophic organisms also hold promise for mitigating stress and promoting preferred behaviors and rewarding events that contribute to positive welfare outcomes.
The presentation will provide an overview of different aspects of RAS-based aquaculture that are relevant to fish welfare, taking into account its design- and technology-related diversity and will comment on future perspectives on the topic.