a 30% reduction of FCR in a trout farm resulted in a reduction of almost 20% of the global environmental impact,excluding energy use (Roque d’Orbcastel et al., 2009c). RAS provides
optimal environmental conditions all year round (total ammonia nitrogen and dissolved CO2 concentrations were lower in the RAS than in the FTS), contributes to fish welfare and minimizes the FCR, hence improving feed efficiency (Losordo, 1998a,b; Roque d’Orbcastel et al., 2009a). Feed impact on the environment may also be reduced by choosing local feed ingredients and ingredients from a low trophic level (e.g. proteins and lipids from phytoplankton rather than fromfish), provided feed digestibility does not decrease.