Rainbow trout in bare concrete tanks lack the environmental complexity of their natural stream habitat. Enrichment provision can improve welfare and also production performance in farmed trout.
Rainbow trout in barren tank environments experience chronic sensory and environmental deprivation compared to their natural habitat. The absence of substrate, cover and hydraulic complexity means that fish cannot perform natural habitat-use behaviours including shelter-seeking, substrate feeding and current-positioning. High aggression rates in barren tanks cause fin damage and scale loss that represent both welfare indicators and welfare costs in themselves. Enrichment provision that increases environmental complexity has been shown to reduce aggression, improve fin condition and normalise group structure. The welfare benefit of enrichment appears to reflect genuine improvement in the experience of tank life rather than merely changed behaviour.