Rainbow trout in recirculating aquaculture systems and flow-through raceways benefit substantially from tank design improvements and environmental enrichment that support natural behaviour and reduce chronic stress.
Trout in barren raceways show elevated baseline cortisol, reduced immune function, and heightened aggression. Subordinate individuals in competitive groups suffer from reduced food access and chronic stress. Environmental enrichment with flow refuges, substrate, or visual barriers reduces agonistic behaviour and improves welfare across all individuals. Tank shape influences welfare — circular tanks with central currents allow trout to school and exercise naturally. Good enrichment reduces injury rates, disease susceptibility, and mortality while improving growth efficiency — making it economically as well as welfare-beneficial.