To breathe below the surface, most fish gulp down water, sending oxygen circulating throughout the body via blood vessels found in the animal’s gill chambers. Once a fish has sufficiently replenished its oxygen levels, it “exhales” the now oxygen-depleted water out of its gill slits and expels carbon dioxide waste at the same time.
Typically, this process occurs fairly quickly. But as a new study published in the Journal of Fish Biology reports, scientists have now identified a fish capable of “holding” its breath—in other words, holding water within the body for an extended period of time before exhaling—for up to four minutes. This evolutionary adaptation, made possible by the coffinfish’s enormous inflatable gill chambers, may help the deep-sea dweller conserve energy in a low-resource environment.
According to Science magazine’s Erica Tennenhouse, co-authors Nicholas P. Long, who conducted the research as an undergraduate biology student at Dickinson College, and Stacy Farina, a biologist at Howard University, first observed the coffinfish’s breath-holding abilities while studying open-access videos recorded by remotely operated vehicles during National Oceanic and Atmospheric Administration (NOAA) expeditions to the Atlantic and Pacific Oceans. To better understand how the animal’s gill chambers work, Joshua Rapp Learn writes for National Geographic, Farina and Long also dissected and CT-scanned specimens housed at Harvard University’s Museum of Comparative Zoology.
Per Live Science’s Yasemin Saplakoglu, the footage shows eight coffinfish, or Chaunax endeavouri, holding large amounts of water in their gill chambers for periods ranging from 26 seconds to four minutes. As Rapp Learn notes, the animals, known colloquially as sea toads, boast such sizable gills that they can increase their body volume by up to 30 percent upon inhaling a significant quantity of water. For comparison, Farina says, this uptick in volume would equate to a human inflating their lungs to the size of the entire abdomen.
In the study, the authors point out that the coffinfish’s “extraordinarily slow ventilation” is well-suited to the species’ sedentary lifestyle. (Giant gill chambers aren’t the coffinfish’s only deep-sea adaptation: The animals also have special fins that enable them to “walk” across the seafloor.)
“They’ve completely adapted to be a seafloor animal,” Long tells Rapp Learn. “They hardly ever swim. Some people call them lazy.”
Sea toads eat infrequently, according to the paper, and generally “consume anything that comes close enough and fits in[to] their mouth.” But this indiscriminate diet isn’t simply the result of gluttonous tendencies; instead, Long explains, it’s “pretty unlikely” that prey will cross a coffinfish’s path on any given day. By dedicating less energy to breathing, the animals may find themselves better equipped to survive in an unfriendly, food-scarce habitat.
It’s also possible that coffinfish, like pufferfish, inflate their bodies as a defense against predators. John Caruso, an ecologist at Tulane University who was not involved in the new study but called the research “excellent,” tells Rapp Learn that this explanation is a “plausible hypothesis.” (He warns, however, that the coffinfish caught on camera may have simply been holding their breath in response to the ROVs’ bright lights.) Hsuan-Ching Ho, a marine biologist at Taiwan’s National Dong Hwa University who described three newly discovered coffinfish varieties in 2016, finds the theory less convincing, pointing out that pufferfish can maintain their shape if squeezed or bitten, whereas coffinfish, which have open gill chambers, would simply leak out water if bitten.
Ultimately, Farina and Long conclude in the study, the coffinfish’s “slow, high-volume ventilation” and breath-holding abilities “support [the species’] survival ... as deep-sea, benthic fishes with a strategy of ambush predation, limited activity and defence against more mobile predators.”