The Food and Agriculture Organization of the United Nations (FAO) was founded after the Second World War with a clear mandate: to raise levels of nutrition, improve access to food, conserve natural resources and help free humanity from hunger. It is promoting major expansion of aquaculture as a means of advancing food security, nutrition and climate action—but without establishing adequate safeguards to ensure that this growth supports those objectives. The FAO climate roadmap calls for at least 75% growth in global ‘sustainable aquaculture’ production by 2040 compared with 2020. Because FAO’s policies shape what governments, development banks, donors and businesses accept as sustainable, its target will influence aquatic food systems, food security, fishing livelihoods and the health of marine ecosystems for decades to come.