Fresh waters in lakes, ponds, rivers, estuaries and wetlands are only 0·3% of available global surface water yet support 47–53% (> 15 000) of all extant fish species. Freshwater fishes are globally valuable yet threatened everywhere through overfishing, pollution, habitat loss, damming, alien invasive species and climate change. Hence, they are in dire need of effective and sustained conservation action, including through zoo and aquarium programmes in the wild and ex situ. To address these challenges, zoo and aquarium staff need to be familiar with the substantial issues, develop greater expertise, and become better integrated in wider regional and global initiatives in freshwater-fish conservation and sustainability. Resolving diverse issues requires knowledge of the many different values in the conservation of freshwater fishes, including sustainable commercial fisheries and the aquarium trade. It is necessary to assess and mitigate threats to fish survival through research and monitoring. An improved conservation-orientated science of threatened fish species is also needed in terms of taxonomy and biology. From this, the implementation and dissemination of appropriate conservation policies, strategies and legislation can be developed. All these factors enable direct practical action for fish conservation, in conjunction with improved zoo education, training and public communication. Finally, review and evaluation of the efficacy of various conservation actions must be carried out in order to plan future undertakings.