© Merve
The Rainbow Trout Operational Welfare Indicator (OWI) Protocol: Ongrowing, Seawater is described by its authors as the first comprehensive, standardised and threshold-based welfare assessment tool developed specifically for farmed rainbow trout in seawater systems.
The protocol brings together 33 operational welfare indicators across three categories: 14 individual-based indicators, five group-based indicators and 14 environmental indicators. These range from body condition, fin damage and sea lice to mortality and feeding behaviour, as well as environmental parameters including stocking density, dissolved oxygen, temperature, salinity and water velocity.
Each indicator is scored from level 0 to 3, with higher scores representing a greater risk of welfare compromise. The system has been aligned with the Laksvel protocol used for Atlantic salmon, while thresholds were developed through reviews of scientific literature relevant to rainbow trout and commercial seawater production.
The guidance is intended primarily for farm staff conducting routine welfare monitoring, but also for certification bodies, auditors and seafood buyers. It has been designed to support welfare assessment requirements under schemes including RSPCA Assured and the Aquaculture Stewardship Council (ASC).
The authors stress that scores should be treated as indicators of welfare risk rather than definitive measures of a fish’s welfare state, and recommend considering multiple indicators together and tracking them over time. They also acknowledge that the evidence base varies considerably between indicators, with some thresholds relying partly on research from Atlantic salmon or freshwater rainbow trout.
The Centre for Aquaculture Progress plans to review the protocol at least every two years as new science, industry feedback and certification requirements emerge.
