In the information age, making informed decisions about food should be straightforward. Consumers increasingly seek trustworthy information on sustainability, nutrition, provenance, and the risks and benefits associated with the products they consume. However, in the case of aquafood, the intersecting complexities of health considerations, environmental sustainability, and climate impacts create a challenging landscape for both consumers and industry stakeholders. To address this, the VeriFish project introduces a robust framework of verifiable indicators designed to support informed and responsible choices among retailers, producers, fishers and citizens. This paper presents the data-driven methodology for constructing a semantic knowledge base that underpins the VeriFish indicator framework by integrating heterogeneous data sources. We outline the key challenges and requirements in building this knowledge base, describe its technical implementation, and detail the mechanisms developed to support discovery and access. Finally, we showcase dedicated applications built on top of the knowledge base that enable practical use of the indicator framework.