A team of scientists from the University of Massachusetts Amherst has found that a major theory explaining why fish are decreasing in size as waters warm may not be true.

Known as the Gill Oxygen Limitation theory (GOL), it has been proposed as the universal mechanism that governs fish size. However, after extensive experiments, researchers found the theory does not appear to hold up.

The GOL theory suggests that as water temperatures rise, fish require more oxygen but their gills cannot supply enough due to a limited surface area.

This supposedly forces fish to shrink in order to adapt. It has been used in global fisheries projections forecasting drastic declines.

To test GOL, researchers studied brook trout over several years. They found while warmer water did decrease fish size as expected, gill surface proved sufficient to meet oxygen needs – contradicting GOL. Surprisingly, the trout’s metabolic rates also adjusted to higher temperatures over time.

Oxygen use may still limit fish size, but our findings show GOL cannot predict what we’re seeing, says lead author Joshua Lonthair of UMass Amherst. This has implications for forecasting climate impacts on future fisheries and ecosystems.

Co-author Lisa Komoroske adds the study highlights the need for interdisciplinary work. Fisheries scientists tend to focus on populations and species, while physiologists study individuals. But to help fish survive warming waters, we must work across all biological scales and pool knowledge.

So what really governs the relationship between fish size and temperature remains unclear. It may not be one mechanism but several factors like oxygen use, says Lonthair.

More long-term interdisciplinary studies are needed to best understand and adapt to our warming world. The researchers’ work provides an excellent example of how scientific collaboration across fields can yield new insights.


University of Massachusetts Amherst | Joshua K. Lonthair, Nicholas C. Wegner, et al., Smaller body size under warming is not due to gill-oxygen limitation in a cold-water salmonid. J Exp Biol 15 February 2024; 227 (4): jeb246477. doi.org/10.1242/jeb.246477

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