Rainbow trout in bare circular tanks show frustration behaviour and reduced welfare — environmental enrichment studies reveal simple interventions can dramatically improve fish welfare outcomes.
Environmental impoverishment in trout production creates frustration through prevention of natural behaviour including shelter-seeking, flow-preferring, and substrate investigation. Stereotypic circling is a welfare indicator in unstimulated fish. Simple enrichment — substrate areas, plastic plants, flow variation — measurably improves welfare without reducing growth. Certification schemes are beginning to include enrichment standards.