Intensive land-based mariculture-systems are flow-troughs or recirculating systems. Flow-through systems are constructed with a water inlet and outlet on opposite ends. Aquatic organisms can be grown in streams of controlled velocity. The Water is used once only and then discharged into the receiving water with or without treatment. Recirculation Systems are closed or partially closed systems employed in aquaculture production. The effluent water from the system is treated and recirculate to enable its reuse. Usually, a relative small portion of the actual culture medium is exchanged per unit time. These systems are also called recirculating aquaculture systems (RAS). It is assumed that the use of recirculating systems in intensive commercial aquaculture will increase in the future. These systems would be preferred for cultures of exotic species and genetically modified organisms (GMOs), because escapes can be prevent. Generally, recirculating systems are used for the culture of high value products such as crustaceans and other marine delicatessens.