Can you imagine seas and oceans completely bereft of colourful fish? The possibility may not be all that far-fetched, thanks to rising carbon dioxide (CO2) emissions. By the end of the century, CO2 concentrations in seas will interfere with fish's ability to hear, smell, turn and evade predators, says Phillip Munday, professor at the ARC Centre of Excellence for Coral Reef Studies and the James Cook University.