Rainbow trout in barren tank systems exhibit abnormal behaviours and elevated stress. Environmental enrichment with current and structural complexity improves welfare significantly.
Rainbow trout welfare in commercial RAS and flow-through tank systems can be substantially improved through environmental enrichment that partially replicates natural stream complexity. Current jets allowing fish to exercise against flow, substrate providing tactile stimulation, and physical shelter reducing social aggression all provide measurable welfare benefits. The welfare improvements are accompanied by production benefits through reduced cortisol-mediated growth suppression, making enrichment a cost-effective intervention. Simple enrichment additions including current jets and substrate trays are low-cost relative to welfare and production gains.