The physical environment of farmed fish — substrate, flow rate, light, shelter — affects welfare as directly as social conditions and diet. Environmental enrichment for fish is an emerging welfare priority.
Wild fish inhabit structurally complex environments with substrate diversity, flow variation, and shelter. Bare tank aquaculture denies all environmental complexity. Gravel substrate provision for trout allows natural resting and foraging behaviour. Artificial shelters reduce aggression by allowing subordinate fish to escape dominant individuals. Flow rate variation in recirculating systems can mimic natural riffle-pool dynamics. Light provision matching natural photoperiods reduces disruption to circadian rhythms in captive fish.