Roque d’Orbcastel et al. (2009c)calculated that energy use through LCA is 1.4–1.8 higher in RAS (63,202 MJ/ton of fish or 16 kWh/kg fish) than in flow-through systems. Energy use reduction in RAS is possible by finding a compromise between an optimal design for water circulation and water oxygenation of the airlift and between the backwash and operation of the bio-filters (Roque d’Orbcastel et al., 2009c) or the incorporation of denitrification in the recycling loop (less make-water means less energy to heat water,Eding et al., 2009). A reduction of transport of feed ingredients in fish feeds will further lower energy consumption.
Table 3shows that the energy consumption per kg of trout or sea bass produced in FTS and RAS is comparable to the amount needed to capture 1 kg of cod at sea (5–21 kW/kg). Recent RAS designs minimize height differences between RAS compartments and also pumps became more efficient or replaced by air lifts. This resulted in a reduction in energy use, a trend that continues considering further improvements such as completely low head RAS with only few
centimetres of height differences or raceway systems that use and treat water alongside
cascades.