To meet the challenges of producing more while lowering impacts on ecosystems, new farming systems have to be designed. To define development strategies, a multi-scale assessment method that estimates the tradeoff between human demand and natural services, as well generates consistent performance indicators on utilization of natural resources and environmental emission levels based on the same set of input data is needed. LCA estimates resource use and potential environmental impacts throughout a product’s life cycle at global and regional scales [1] but does not consider the provision of ecosystem services or products [2]. Emergy accounting (EA) is an ecology-based tool developed to integrate all system inputs (environmental and economic values) using a common unit, solar emergy joule [3]. EA inserts the productive cycle into a local environmental context and quantifies the energy flows between the environment and the production system. Through three contrasting fish-farming systems, we attempted to demonstrate the interest of a combination of LCA and EA to define the major components of environmental sustainability and ecological intensification of fish farming and more globally of agricultural systems. The first system is a recirculating system (RSF) of Atlantic salmon depending highly on external inputs (feed and energy). The second one is extensive fish polyculture in a pond (PF1) with few external inputs. The last one is a small pond farm with use of external feeds. These systems were assessed according the ISO standards for attributional LCA during one production year. The assessment covered farm operations and transportation at all stages. Local emissions of nutrients were estimated using nutrient balance modeling and pond emissions were refined to include nitrogen-fate factors. LCA results are presented as traditional midpoint indicators according CML 2 baseline 2001and are expressed by tonne of fish produced. Emergy accounting [3] is based on LCA system definition but includes also the contributions of natural systems (sun, rain, groundwater, etc.) and provide indicators to evaluate the efficiency of energy use and its quality during the lifecycle. The chosen Emergy indicators are: Percentage of renewability (%R); the Emergy Yield Ratio (EYR, ability to rely on local resources; Environmental Loading Ratio (ELR, level of exploitation of nonrenewable resources compared to renewable ones). For 1 tonne of living fish, RSF had higher potential impacts for NPPU and all the Emergy indicators (Figure 1). PF2 had higher potential impacts in comparison with PF1 except for water dependence. However, RSF had lower potential impacts for climate change, eutrophication, land competition and water dependence than ponds, which reflects the level of intensification of the systems. The consumption of energy (calculated by LCA, Figure 2) was similar for RSF and PF1 and higher for PF2. But, the contributors to this impact differed among the systems (direct energy use for ponds and feeds and direct energy used for RSF). The difference in %R between systems was due to water origin: for RSF water was pumped whereas for ponds it came essentially from rain and water run-off. PF1 has a higher EYR, which means that it depends less on market resources than RSF. The RSF higher value of ELR (7.98) indicates a moderate environmental impact. The combination of LCA and Emergy accounting on contrasting systems provides a perspective of what ecological intensification could mean in aquaculture: a decrease in potential impacts per unit mass of final products, especially for global warming, eutrophication and acidification; a decrease in dependence on market-based and external resources; and an increase in the use of renewable natural resources and input efficiency. This is particularly true for choices regarding feed ingredients and the origin of energy sources.