I love fishing. As with every fisherman, I have my fair share of "the one that got away" stories steeped in *mostly* truth. So, you can imagine my interest in reading research that shows fish appear to be shrinking in warming waters.
Warm waters carry less oxygen, which makes it difficult for fish to breath...especially larger fish. Metabolism is also higher in fish living in warm waters. Higher metabolism means the fish need more oxygen. The gills of fish are responsible for extracting oxygen from water and when they reach their maximum ability to provide oxygen, fish stop growing. According to estimates presented by Drs. Daniel Pauly and William Cheung from the University of British Columbia in Vancouver, fish could grow as much as 30% smaller with only a 1 degree Celsius increase in temperature and as much as 45% smaller with just a 2 degree Celsius increase.
Pauly D, Cheung WWL. Sound physiological knowledge and principles in modeling shrinking of fishes under climate change. Global Change Biology. Published online August 21, 2017..