Management of aquaculture farms needs to constantly monitor production parameters with the aim of optimizing technical efficiency of production cycles, to reduce production costs and to enhance competitiveness and sustainability. A benchmarking tool, based on Key Performance Indicators (KPIs), was built to benchmark biological capacity, cost-efficiency, fish health and welfare and environmental performance of marine Mediterranean fish farming industry. The KPI tool was developed in close collaboration with the five fish farming Producer Associations (APROMAR, FGM, API, CCE-CAA, SFAMN), aggregating the major European aquaculture companies, RD&I aquaculture managers and scientific partners. It was specifically designed for sea bass and sea bream aquaculture and for being applied to the whole production cycle, from hatchery to grow-out till harvest, excluding the processing phase. The tool includes 55 Key Performance Indicators: 35 KPIs Technical-KPIs (T-KPI) to measure the technical performances, as growth, feed efficiency, deformities, losses, diseases and use of antibiotics and antiparasitic compounds 9 Welfare KPIs (WE-KPI) to assess welfare during fish farming husbandry practices 14 Environmental KPIs (E-KPIs) to measure the use of land, water and energy required for fish production and to estimate the impact of farming practices on marine habitat and biodiversity 2 Key Economic Performance Indicators (EC-KPIs) to measure the productivity and efficiency of aquaculture farms.