In some cases, the critical resource is water, and the intensification of tank systems
consists of increasing production with the available water supply (i.e., increase production
in terms of mass produced per volume of water used, or kg/l). In other cases, the critical
resource may be space, in which case, intensification may consist of increasing the
production density (i.e., increase production in terms of mass produced per area per time,
or kg/m2
/year). While intensification in tank systems may be achieved without water
recirculation (e.g., through the use of pure oxygen only), it normally includes some other
form of water treatment and reuse. The degree to which water is reused and the system
becomes a tank recirculation aquaculture system (RAS) is highly variable. In fact, the
point at which a system may be described as a RAS is, to a large extent, arbitrary. The
impact on effluents ultimately depends on how intensification is implemented and the
extent and characteristics of the water treatment processes used.