But fish around the world are getting smaller as their habitats get warmer.

For example, important commercial fish species in the North Sea have declined in size by around 16 per cent in the 40 years to 2008, while the water temperature increased by 1–2C. This "shrinking" trend is forecasted to significantly exacerbate the impacts of global warming on marine ecosystems.

The link between warmer water and smaller size is well known, but poorly understood. Our experiments keeping fish in warmer water offer some crucial clues — and may help us learn how to prepare for a warmer future with smaller fish.