This thesis is divided into four main chapters. Chapter 1 gives definitions and describes the context and problems of fishing to which the stock assessment is related, in particular: Ecosystems, and Fishery and Fish Stock Assessment. Some biological characteristics of the Common Sole (Solea Solea) are introduced and the stock assessment of this demersal fish is derived from a recent scientific survey, SoleMon, made by specialized marine biologists. Chapter 2 sets the computer science context elaborating on the Agent-base Paradigm and on Agent-based Modelling and Simulation. Chapter 3 describes the theory and the background of the developed model and simulator, giving an overview of Repast Simphony, the agent-base platform over which the DISPAS simulator is developed. Moreover, experimental results, the validation of such results and some preliminary predictions made using the simulator are also presented in this chapter. Finally, Chapter 4 concludes and gives several directions for future work.