The fish farming industry is one of the fastest-growing industries and will be one of the most important businesses in the future. However, more salmon than ever died prematurely in Norway in 2021, mainly due to diseases and lice treatments. Sharing data related to lice is crucial for improving the situation. However, to facilitate data sharing, a platform for storing data, data comparability, and trustworthy relationships must be secured. Sharing data poses challenges that require proper governance. Based on a longitudinal, qualitative case study of a collaborative platform ecosystem in the Norwegian aquaculture industry, we identify governance mechanisms that enable data sharing. Furthermore, we develop a model for the gradual maturation of data sharing. Our insights from a collaborative platform ecosystem within a traditional industry complement the extant research, mainly focused on centralized platform ecosystems. We also provide guidance for practitioners who want to enable data sharing in their ecosystems.