Fish and other aquatic foods (blue foods) present an opportunity for more sustainable diets 1,2 . Yet comprehensive comparison has been limited due to sparse inclusion of blue foods in environmental impact studies 3,4 relative to the vast diversity of production 5 . Here we provide standardized estimates of greenhouse gas, nitrogen, phosphorus, freshwater and land stressors for species groups covering nearly three quarters of global production. We find that across all blue foods, farmed bivalves and seaweeds generate the lowest stressors. Capture fisheries predominantly generate greenhouse gas emissions, with small pelagic fishes generating lower emissions than all fed aquaculture, but flatfish and crustaceans generating the highest. Among farmed finfish and crustaceans, silver and bighead carps have the lowest greenhouse gas, nitrogen and phosphorus emissions, but highest water use, while farmed salmon and trout use the least land and water. Finally, we model intervention scenarios and find improving feed conversion ratios reduces stressors across all fed groups, increasing fish yield reduces land and water use by up to half, and optimizing gears reduces capture fishery emissions by more than half for some groups. Collectively, our analysis identifies high-performing blue foods, highlights opportunities to improve environmental performance, advances data-poor environmental assessments, and informs sustainable diets.The food system is a major driver of environmental change, emitting a quarter of all greenhouse gas (GHG) emissions, occupying half of all ice-free land, and responsible for three quarters of global consumptive water use and eutrophication 3,6 . Yet, it still fails to meet global nutrition needs 7 , with 820 million people lacking sufficient food 8 and with one in three people globally overweight or obese 9 . As a critical source of nutrition 8,10 generating relatively low average environmental pressures 1,2,11,12 , blue foods present an opportunity to improve nutrition with lower environmental burdens, in line with the Sustainable Development Goals to improve nutrition (Goal 2), ensure sustainable consumption and production (Goal 12), and sustainably use marine resources (Goal 14).Blue foods, however, are underrepresented in food system environmental assessments 13 and the stressors considered are limited 4 such that we have some understanding of GHG emissions 14,15 , but less of others such as land or freshwater use 16 . Where blue foods are included, they are typically represented by only one or a few broad categories (see, for example, refs.
3,17,18), masking the vast diversity within blue food production. Finally, estimates combining results of published life cycle assessments undertaken for different purposes, and consequently using incompatible methodologies 19,20 , cannot be compared reliably. It is therefore critical to examine the environmental performance across the diversity of blue foods in a robust, methodologically consistent manner to serve as a benchmark within the rapidly evolving se...