Warming temperatures in the sea as a result of climate change could shrink fish by 20% to 30%, says a new study by two researchers at the University of British Columbia in Canada. The study, titled “Sound Physiological Knowledge and Principles in Modeling Shrinking Fishes Under Climate Change”, was published in the journal Global Change Library.

In a statement on Tuesday, Associate Professor at the Institute for the Ocean and Fisheries and William Cheung said fish cannot regulate their own body temperatures as they are cold-blooded animals. “When their waters get warmer, their metabolism accelerates, and they need more oxygen to sustain their body functions,” said Cheung, who co-authored the study.

However, warming seas are already reducing the availability of oxygen in some parts of the ocean. So when the gills stop supplying enough oxygen for a larger body, the fish stops growing, he explained.

Daniel Pauly, the study’s lead author and a professor at the Institute for the Ocean and Fisheries, said that as fish grow, they need more oxygen. But the gills do not grow at the same pace, which will mean even lesser oxygen.

Smaller fish like tuna will be affected more than others as they are fast-moving and need more oxygen for energy.