Scientists from the University of Massachusetts Amherst have found no physiological evidence to support the Gill Oxygen Limitation (GOL) theory, which posits that fish are shrinking due to increased water temperatures affecting their gill surface area. Their long-term experiments on brook trout showed that while the fish were smaller in warmer temperatures, their gill surface area was sufficient for their energy needs. This suggests that factors other than gill surface area, such as oxygen use, may be influencing fish size in warmer waters, challenging the GOL theory that has been used in predictions of future global fisheries yields.