Aquaculture is the fastest-growing food producing industry sector in the world. Demand for feed ingredients, particularly for preferred protein sources such as fishmeal, fish oil and ‘trash fish’, has also increased, raising questions about sustainability and uses of fish for aquaculture feeds or directly as human food. Approximately 30 million metric tonnes (MMT) of fish from capture fisheries are used each year to produce fishmeal and fish oil. The species used are not usually consumed directly by humans. Production of fishmeal and fish oil has remained relatively static over many years, with the increasing amount going to aquaculture feeds being balanced by reducing amounts going to other animal feeds. Trash fish are generally smaller or lower-value species captured in the wild and are increasingly used to directly feed aquaculture species in Asia. Although there is no reliable estimate of the total amount of trash fish used by aquaculture, the figure is probably >5 MMT y–1. As aquaculture expands, the potential for conflict between uses and users of different fish products is increasing. There is an urgent research priority to identify potential impacts of increasing demand on trash fish for aquaculture on fish resources and to identify practical alternatives. The identification and use of alternative ingredients for aquaculture feeds has been an international research priority for at least 15 y, and significant advances have been made. Fishmeal has been completely replaced in feeds for many species and included at very reduced levels in feeds for many others. These trends need to continue and ongoing research in this field remains a priority. Research to replace fish oil is more difficult, but blends of vegetable oils have been used to successfully reduce reliance on fish oil for a number of species. Coldwater marine algae called thraustochytrids, with very high contents of ‘marine’ fatty acids, may provide an alternative if industrial-scale fermentation can be made cost effective.