Developing operational welfare indicators for European Sea bass (Dicentrarchus labrax): Delphi-informed reflections on advancing farmed fish welfare

Examining consensus among fish farmers, scientists, and regulatory authorities is critical for the development and implementation of effective animal welfare assessment schemes. Aquaculture researchers provide scientific data on fish needs, and evidence-based welfare indicators that accurately reflect fish physical and affective state. Fish farmers take care and bring empirical insights into what is feasible in day-to-day routine operations, while the competent authorities play a key role in official controls and in aligning welfare schemes with legal standards and policy objectives. To ensure that these diverse perspectives are meaningfully integrated, structured participatory approaches are needed to build shared understanding and agreement. This study employs a modified Delphi method bringing together various relevant stakeholders to identify and evaluate Operational Welfare Indicators (OWIs) for on-growing European sea bass, Dicentrarchus labrax , in net-pen sea cages. Through iterative questionnaires and discussion via an online tool, the SmartDelphi platform (INNEX LABS, Barcelona, Spain), experts prioritised water quality, behaviour, and health metrics as key OWIs. They also highlighted major welfare challenges and proposed improvements for an objective, reliable and effective on-farm welfare monitoring. The findings offer a social approach for prioritising welfare indicators, incorporating them into farm management and welfare assessment schemes for European sea bass and suggest directions for further research across species and rearing systems. • A modified Delphi method was used to identify key operational welfare indicators (OWIs) for European sea bass. • Input and outcome welfare indicators were rated according to their usefulness. • Findings support evidence-based, feasible welfare monitoring for on-farm application.