Pufferfish don't hold their breath

ocean fish
CC BY 2.0 carlos.miguelanez

For a long time scientists believed that pufferfish held their breath to stay puffed. As soon as they feel threatened, puffer fish will gulp large amounts of water into their stomachs and swell three to four times their usual size.

It's easy to see why researchers might have thought pufferfish couldn't respire with their stomachs full. If you puff out your chest, you'll find it's hard to breathe. It's even harder to stay puffed when your inhaling and exhaling - there's only so much puffing your muscles can do without a bag of air pushing them outwards. Scientists also noticed that one type of pufferfish - the Obscure pufferfish - would keep its gills firmly shut when it inflated.

But biologists from James Cook University and the Australian Institute of Marine Science weren't convinced - so they decided to conduct some experiments.

"We were intrigued by previous studies that suggested the pufferfishes hold their breath while inflated, presumably to keep the ingested water in the stomach," Georgia McGee, who did the research, told Discovery. "If this was true, we thought it likely that pufferfish inflation would have a limited duration, due to a lack of oxygen getting to vital body organs."

McGee and her team took eight puffers and placed them in custom-made devices that measure respiration. They then tricked the fish into thinking they were under threat by squeezing them gently and applying a bit of suction.

When the fish puffed up, the biologists noticed that oxygen levels in the water around them was dropping and that the fish were taking in oxygen through their gills. Myth busted: pufferfish don't hold their breath.

But still, inflating isn't an ideal situation for puffers. Though it helps them avoid getting swallowed, it weakens their metabolism and they become more susceptible to being eaten once they've returned to their normal size. It takes hours for the fish's metabolism to recover from the exercise.

Pufferfish don't hold their breath
It turns out puffers can breathe when they feel threatened