Method

OWI selection process

This protocol selected OWIs through a comprehensive analysis of existing OWI frameworks and materials, a complete list of which is in the Appendix under “OWI selection”.

The selection process involved:

• Structured review of indicators used in established protocols (e.g., Laksvel for Atlantic salmon and APROMAR’s ‘A guide on fish welfare in Spanish aquaculture - volume 3: Welfare of gilthead sea bream’).¹³
• Review of other materials considering operational welfare indicators, including those published by industry.
• Analysis of certification requirements from major schemes (e.g., ASC).
• Consideration of commercial need for the indicator to be included, scientific validity, practical feasibility, and welfare relevance for gilthead sea bream.

Threshold development process

Scoring thresholds were aligned with the system used in our previously published Rainbow Trout Operational Welfare Indicator (OWI) Protocol: Ongrowing, Seawater,¹⁴ which in turn was based on Laksvel. Threshold recommendations for each OWI were developed through an indicator-specific structured review of the current scientific literature, prioritizing evidence from ongrowing gilthead sea bream in commercial conditions. Where such evidence was limited (which was often the case), the analysis incorporated evidence from laboratory settings, alternative life stages, or other species, as well as expert opinions.

Each paper was evaluated based on the following criteria:

• Quality: Study design, sample size, peer review status, etc.
• Indicator relevance: How directly the study investigated the impact of a specific indicator on welfare.
• Context: How closely the study context and findings apply to ongrowing gilthead sea bream in commercial production, considering laboratory/commercial conditions, life stage, environmental conditions (e.g., stocking densities), and species.

Papers were qualitatively graded as high, moderate, low, or very low according to the quality and relevance of each study (considering factors such as study design, sample size, duration, and applicability to commercial gilthead sea bream) with stronger and more relevant evidence given greater weight in setting the threshold recommendations. This approach ensures the recommendations are grounded in the best available science while providing practical guidance where specific knowledge gaps exist.