Reference: Long NP, Farina SC. Enormous gillchambers of deep-sea coffinfishes (Lophiiformes:Chaunacidae) support unique ventilatory specialisations suchas breath holding and extreme inflation.J Fish Biol. 2019;95:502–509. https://doi.org/10.1111/jfb.14003
As you swim through a coral reef, you see parrot fish, clams and other colorful aquatic creatures swimming elegantly and going about their lives. While you, with your snorkel, are confined to the surface of the water and the occasional dive for as long and as deep as you can hold your breath, the fish “breathe” easily with their gills (or lungs in the cases of some evolutionarily interesting fish). But do they breathe that easily? Living in and getting oxygen from a high-pressure aquatic environment is difficult and metabolically demanding, and some fish have found special ways to make it easier.
Nicholas Long and Stacy Farina, researchers at Dickinson College and Howard University, looked at a peculiar and charismatic fish (Lophiiformes: Chaunacidae) and the way its gill ventilatory system works. This fish, also known as coffinfish or the sea toad, is a deep-sea anglerfish. Like other anglerfish it is an ambush predator, waiting motionlessly for prey and then suddenly snatching up any edible thing that comes near. Living in the high pressure and low temperature depths with very little light and food, coffinfish have adapted to use as little energy as possible while waiting for prey. Unlike other fish that can pump force water over their gills as they move forwards (a process called ram ventilation), coffinfish are often sedentary and need other ways to get as much oxygen using as little energy as possible.
Gulping for Breath
Deep-sea critters like coffinfish are tough to study because of their inaccessibility, so Long and Farina used coffinfish footage from remotely operated vehicles—essentially robotic submarines—from the National Oceanic and Atmospheric Administration, paired with studies of their skeletons from the Museum of Comparative Zoology. The footage of deep-sea encounters with coffinfish show them inflating their gill chamber with water, essentially holding their “breath.” The fish can sit with their gill chambers full of water for a few seconds to several minutes.
While it is not completely clear why they do this, Long and Farina pose several advantages to this holding of water in their gill chambers. This behavior reduces energy usage and allows them to go for long periods of time without food. Less frequent gill ventilation also reduces disturbance of water near it so it can better sense disturbances from other creatures in the dark depths, all the while remaining effectively invisible to those same creatures. Holding its “breath” also puffs up the fish, a useful defense mechanism that makes it too big for some predators to chomp on and looks visually threatening. This defense mechanism is superficially similar to that of pufferfishes but is accomplished by a very different and unique mechanism. Some of the deep-sea footage even show coffinfish puffing up, when angered or startled by the remotely operated vehicles used in the study.
Holding your breath may not be unique to land-dwellers anymore and may not even be unique to just coffinfish among the marine fauna. It is possible other fish living in the depths employ similar breathing mechanisms, and while these elusive animals may have not been spotted yet, they may be seen in future ocean explorations. To see coffinfish and other deep marine oddities, look at the National Oceanic and Atmospheric Administration’s ocean exploration footage, all publicly available with new discoveries being made every year through the Ocean Exploration and Research expeditions.
Video by Stacy Farina of a coffinfish exhaling, from NOAA remotely operated vehicle footage: