How closed is “closed”? Ambiguity in British Columbia’s Closed Containment aquaculture regulations

<jats:p>We examine disease-transmission risks to wild salmon associated with containment technologies proposed in 2025 under British Columbia’s transition away from open-net pen aquaculture. To ensure consistent terminology, and to avoid the mischaracterization of marine “semi-closed” flow-through systems as “closed containment,” we clarify categories of aquaculture production technologies and compare their containment effectiveness and pathogen risks in relation to current Fisheries and Oceans Canada definitions. While semi-closed systems may reduce parasite infestations such as sea lice, they do not protect farmed or wild fish against microbial pathogens unless inflow and effluent water are effectively treated. The effectiveness of water treatment and filtration in marine semi- and fully-closed containment systems is central to risk reduction and should be evaluated under the precautionary principle through rigorous testing of new technologies to verify efficacy. Our findings underscore the need for robust monitoring, transparent reporting, and adaptive regulatory oversight to ensure that innovation in aquaculture technology genuinely reduces pathogen transmission and protects wild fish.</jats:p>