This book synthesises the role of data, modelling, and Artificial Intelligence in aquaculture. It explains how these technologies can be used to construct a "digital twin" - a virtual representation of a fish farm - that provides operators with deeper insights into farm processes, helps identify efficiency pathways, and supports the study of performance issues. The book outlines the fundamental components of a marine digital twin, including data collection, data processing, and data generation. It discusses the diverse datasets generated on farms and how these can be interrogated using Artificial Intelligence and numerical simulation to extract valuable insights. Several real-world case studies are presented to illustrate these approaches in practice.