February 22, 2024 — A collaborative team of scientists led by the University of Massachusetts Amherst recently found that there is no physiological evidence supporting a leading theory—which involves the surface area of fish gills—as to why many fish species are “shrinking” as waters grow warmer due to climate change. Known as the Gill Oxygen Limitation (GOL) theory, it has been proposed as the universal mechanism explaining fish size and has been used in some predictions of future global fisheries yields.
However, the researchers, representing the National Oceanic and Atmospheric Administration, U.S. Geological Survey, the University of California Davis as well as UMass Amherst, conducted a series of long-term experiments on brook trout and found that though increased temperatures do lead to significantly decreased body size, gill surface area did not explain the change. The results of the study were recently published in the Journal of Experimental Biology.
“We know that global climate change is happening and our oceans and rivers are getting warmer,” says Joshua Lonthair, lecturer in biology at UMass Amherst and the paper’s lead author. “And we know that many animals—not just fish—are growing to smaller adult body sizes under warmer temperatures. We even have a name for this, the Temperature Size Rule. But despite decades of research, we still don’t understand why size decreases as temperature increases.”
In both marine and freshwater fish species, rising water temperatures have a critical effect on metabolism, reproduction and other life functions, but a critical factor that most of the models underlying fisheries management rely on is fish size. Commercial fisheries are often regulated by tonnage, and when fish shrink, it takes more of them to fill out a ton. Lower weight is also linked to reduced reproduction. Altogether, this means that managers need to adjust their models for our changing world.