Warmer waters as a result of climate change could shrink the size of fish by 20 to 30 percent, a new study by researchers at the University of British Columbia (UBC) has claimed.

In a statement on Monday, co-author William Cheung said that fish, as cold blooded animals, were not able to regulate their body temperatures.

When the waters they are in become warmer their metabolism accelerates, and they require more oxygen to sustain their body functions. "There is a point where the gills cannot supply enough oxygen for a larger body, so the fish just stops growing larger," Cheung added.

Lead author Daniel Pauly said that when fish grow into adulthood their body mass becomes larger and their demand for oxygen grows.

The surface area of the gills, where oxygen is gathered, does not grow at the same rate as the rest of the body. Pauly described this as the "gill-oxygen limitation theory."

The impacts of climate change are already being felt by some animals. The WWF has described polar bears, for example, as the "poster child for the impacts of climate change on species." Polar bears' reliance on sea ice, according to the WWF, makes them "highly vulnerable" to a changing climate.

The UBC study, "Sound physiological knowledge and principles in modeling shrinking fishes under climate change", was published in the journal Global Change Biology.