Read our COVID-19 research and news.

Spotted for the first time: a fish holding its breath underwater

Like us, fish need oxygen to survive. But to breathe, most pull oxygen-containing water into their mouths and pump it through their gill chambers before expelling it out of their gill slits. Now, for the first time, scientists have seen fish “holding” that breath, some for up to 4 minutes at a time.

The scientists didn’t set out to catch such persistent fish. Instead, they stumbled on videos of coffinfish, a rarely studied group that lives on ocean bottoms throughout the world, captured by remotely operated vehicles in a National Oceanic and Atmospheric Administration expedition.

The videos, shot in multiple locations in the Atlantic and Pacific oceans, show eight deep-sea coffinfish holding large quantities of water in their gill chambers without any signs of inhaling or exhaling. When the coffinfish finally release the water minutes later, their bodies deflate by 20% to 30% (above). It’s their enormous gill chambers that let these fish store such large volumes of water for several minutes, the researchers report in the Journal of Fish Biology.

Why do they do it? The researchers suggest that holding their breath for long stretches may help the notoriously lazy coffinfish conserve the energy they would otherwise use to actively pump water. Puffing up to such a massive size may also serve as a warning to would-be predators.