About the only thing that aquacultural engineers can unanimously agree upon is that a body of water is required to raise fish. How this body of water should be contained is open to considerable debate. Should the fish be reared in ponds, raceways, or tanks? If tanks are chosen, to what geometry should the tank conform? How deep should a tank be or more descriptively, what should the tank diameter to depth ratio be? First, this module is restricted to tank culture and Recirculating Aquaculture Systems (RAS) technology. Therefore, we are only addressing tanks and not open ponds. Within that chosen focus, the paramount issue in all tank culture design is to maximize the capability of the tank system for self-cleaning. Without exception, the dominant reason RAS's fail is their inability to self-clean. A system that does not effectively and quickly remove manure from the culture water will never produce fish economically. All individual components of the system will fail to perform efficiently. Thus, the first question that one should ask is whether or not the tank will effectively clean. Secondly, the capability to effectively manage the fish within the tank vessel is the next question that must be addressed. These and other issues will be addressed in this module. And for the stubborn, raceway design will also be reviewed briefly as will a newly designed hybrid of raceway and round tank concepts. All these concepts can be generally applied to either RAS or flow-through systems.