The Dutch finfish aquaculture sector is unique in Europe and worldwide. This innovative sector is based solely on recirculation aquaculture systems (RAS). RAS are land based fish production systems in which water from the rearing tanks is re-used after mechanical and biological purification to reduce water and energy consumption and to reduce nutrient emission to the environment. The water consumption in RAS is entirely based on water exchange to compensate for evaporation, incidental losses and to control water quality. Because of its controllability, water temperatures in a RAS are kept constant at the optimal rearing temperature for the target species.