A bioeconomic model for the simulation and the optimal management of a fish farm for sea bass Dicentrarchus labrax is presented. Growth and mortality, considered as a Markovian process, are described by a biological submodel, taking into account the effects of water temperature, feeding level, oxygen content, and water supply. Stochastic effects in growth and mortality, relating to the effects of genetic differences, can be also considered in the model. An economic submodel evaluates costs and revenues relating to plant management. The model exhibits good capabilities in predicting the effects of operating variables on fish growth and on economic outcomes and in determining the optimal strategies for plant management in different scenarios, considering the complex interactions of technical, biological, and economic aspects.