Marine By-Products in the Protein Transition: Stakeholder Insights and Adoption Pathway from Five EU Countries

Marine biomass represents a nutrient-rich and underutilized resource with significant potential to contribute to the alternative protein transition. In the European Union (EU), the valorization of marine by-products aligns with strategic objectives related to circularity, resource efficiency, and the blue bioeconomy. This study investigates stakeholder perspectives on the use of marine by-products for food and feed applications across five EU countries (Germany, Hungary, Poland, Portugal, and Spain). Qualitative data were collected from 62 stakeholders representing diverse positions along the food and feed value chains, including primary production (aquaculture and mixed farming), food processing and manufacturing, feed and animal nutrition, ingredient supply, research institutions, innovation actors, and industry associations. A deductive thematic analysis examined key domains such as desired product attributes, sustainability, cost, regulation, and consumer acceptance. Findings indicate that adoption is not driven by a single determinant, such as sustainability appeal or consumer demand. Rather, marine-based protein integration emerges through the interaction of technical feasibility, regulatory legitimacy, economic viability, and socio-cultural acceptance. Based on these insights, a stakeholder-derived adoption pathway is proposed. While country-specific differences were identified, the findings suggest that many adoption barriers are largely structural and shared across stakeholder contexts. Overall, study advances understanding of marine-based proteins within broader sustainability transition processes and provides a systems-oriented framework to inform policy and innovation strategies.