Can Turtles Breathe Through Their Butt?

Some turtles genuinely extract oxygen from water through their rear end, and the process is far more sophisticated than the crude phrasing suggests. The scientific term is cloacal respiration, and in certain freshwater species it accounts for a large share of their total oxygen intake while submerged. The anatomy involved, the species that rely on it, and the surprising way it has inspired medical research in mammals all make this one of the more fascinating corners of reptile biology.

What Cloacal Bursae Actually Do

Turtles have a single rear opening called the cloaca that serves the reproductive, urinary, and digestive systems. In several freshwater species, a pair of thin-walled sacs called cloacal bursae branch off from this opening. These sacs are richly lined with tiny, finger-like projections called papillae, which are packed with blood vessels. The turtle rhythmically pumps water in and out of these sacs, and dissolved oxygen in the water passes across the thin tissue walls directly into the bloodstream, much the way oxygen crosses lung tissue during normal breathing.

The Fitzroy River turtle (Rheodytes leukops) of Queensland, Australia, is the most extreme known example. Its cloacal bursae are greatly enlarged and heavily vascularized, and the species relies on them as its chief means of extracting oxygen from the water.¹ This turtle can stay submerged for extraordinarily long periods, sometimes barely surfacing at all in well-oxygenated water. It pumps water through its cloaca in a steady rhythm, essentially “breathing” underwater the way a fish uses gills, just from the opposite end of the body.

How Much Oxygen Can a Turtle Get This Way

The numbers are striking. In the white-throated snapping turtle (Elseya albagula), another Australian freshwater species, aquatic respiration overall meets about 70% of the animal’s oxygen needs while submerged. The cloacal bursae alone account for roughly half of that aquatic oxygen uptake, making them the single most important site for underwater gas exchange in the species.² When researchers experimentally blocked the cloacas of these turtles, their reliance on aquatic respiration dropped significantly, confirming that the bursae were not just supplementary but central to the animal’s oxygen supply.

The Fitzroy River turtle takes things even further. It is so reliant on cloacal breathing that when dissolved oxygen levels in the water drop, the animal does not simply swim to the surface more often. Instead, it slows its heart rate and shifts into an oxygen-conservation mode designed to stretch out its dive time.³ In normal oxygen conditions, these turtles rely heavily on cloacal respiration; when oxygen drops, they switch strategies to conserve what they have. This behavioral flexibility shows how deeply integrated the cloacal system is with the animal’s overall physiology.

Smaller Turtles Are Better at It

Body size plays an important role in how effectively a turtle can breathe through its cloaca. Smaller Elseya albagula turtles have a relatively larger cloacal bursae surface area compared to their body mass, which allows them to extract proportionally more oxygen from the water.⁴ This is a familiar pattern in biology: as an animal grows, its volume increases faster than its surface area, so structures that depend on surface-area-to-volume ratios become relatively less efficient.

For young turtles, this means cloacal breathing can cover a larger fraction of their oxygen demands. As they grow, they become increasingly reliant on surfacing to breathe with their lungs. This shift does not mean the bursae stop working in adults, just that their contribution becomes a smaller piece of the total oxygen budget. For a hatchling or juvenile, though, cloacal respiration may be the difference between staying safely hidden at the bottom and risking a trip to the surface where predators wait.

Not Just the Butt: Other Ways Turtles Breathe Underwater

Cloacal bursae get the attention because of the novelty, but they are not the only way turtles exchange gases underwater. Some species absorb oxygen through the lining of their throat in a process sometimes called buccopharyngeal respiration. The Chinese soft-shelled turtle (Pelodiscus sinensis), for example, pumps water in and out of its mouth and throat while submerged. In experimental measurements, throat breathing accounted for about 23% of the animal’s total oxygen uptake, while oxygen absorbed directly through the skin contributed another 13%.⁵

Soft-shelled turtles in general have thin, leathery shells and highly vascularized skin, which makes cutaneous gas exchange more feasible for them than for hard-shelled species. The throat-pumping method and the skin route are anatomically different from cloacal breathing, but the underlying principle is the same: pass water over a thin, blood-vessel-rich surface and let oxygen diffuse across. Different turtle lineages have independently evolved different versions of this trick, which hints at how useful it is for animals that spend long periods underwater.

Surviving Winter Without Any Oxygen at All

While cloacal and other forms of aquatic respiration help turtles stay submerged for long stretches, some species face a more extreme challenge: spending the entire winter under ice, where surfacing is impossible. Painted turtles and snapping turtles in northern North America routinely hibernate submerged in ponds that freeze over for months. In well-oxygenated water at low temperatures, freshwater turtles can often meet all or most of their oxygen needs through aquatic respiration. But painted and snapping turtles go further: they can survive four to five months with no oxygen at all.⁶

This is not breathing in any sense, cloacal or otherwise. It is tolerance of total oxygen deprivation. The turtles slow their metabolism to a crawl, and as lactic acid builds up from anaerobic processes, their shell and bones act as a chemical buffer. The minerite of the shell releases calcium and magnesium carbonates into the bloodstream, neutralizing the acid, while also absorbing and storing lactic acid directly.⁷ After 125 days without oxygen at 3°C, painted turtles in one experiment had plasma lactate levels almost a hundred times higher than normal, and both shell and bone had absorbed enormous quantities of lactate.⁸ The shell, in other words, doubles as a chemical life-support system. It is one of the most extreme survival strategies in vertebrate biology.

The distinction matters: the Australian turtles famous for butt-breathing live in flowing, warm rivers where dissolved oxygen is available. The painted turtles trapped under ice in a Minnesota pond are solving a completely different problem. Both adaptations help turtles survive long submersion, but through entirely different mechanisms.

Why Dams and Low Oxygen Threaten These Turtles

If your breathing strategy depends on dissolved oxygen in the water, anything that lowers oxygen levels is a direct threat. River impoundments created by dams tend to have lower dissolved oxygen because water moves more slowly and sits deeper behind the dam wall. For species like the endangered Mary River turtle (Elusor macrurus), which relies on cloacal respiration, this is a serious problem. Research on the species found that long-term low oxygen conditions behind dams impair the turtle’s diving ability and disrupt the respiratory physiology that allows it to stay submerged.⁹

A turtle that cannot stay submerged for long periods is more exposed to predators and more likely to be displaced from its preferred habitat. For species already listed as endangered, the compounding effect of dam-induced oxygen loss on top of other pressures like nest predation and habitat loss makes conservation considerably harder. The trait that makes these turtles remarkable, their ability to breathe underwater through cloacal bursae, also makes them unusually vulnerable to a specific kind of environmental degradation that most land-dwelling animals would barely notice.

Most Turtles Cannot Do This

It is worth being clear about how widespread cloacal breathing actually is, because the internet tends to present it as a universal turtle feature. It is not. The species with well-documented, functionally significant cloacal bursae are concentrated among certain Australian freshwater turtle families, particularly the Chelidae. The Fitzroy River turtle and the white-throated snapping turtle are the best-studied examples. A handful of other freshwater species have some degree of cloacal gas exchange, but in many turtles the cloaca plays no meaningful respiratory role at all.

Sea turtles, for instance, are obligate lung-breathers. Terrestrial tortoises have no need for aquatic respiration. Even among freshwater turtles, the degree to which the cloacal bursae contribute varies enormously. Some species have small, poorly vascularized bursae that may serve other functions, like water absorption, without contributing much to breathing. The popular framing of “turtles breathe through their butts” is true for a few species and misleading for most others.

Medical Research Inspired by Intestinal Gas Exchange

The idea that a rear-end opening could serve as a backup breathing organ has not been lost on medical researchers. In 2021, a team in Japan published work showing that mammals could be oxygenated through their intestines in a method they called enteral ventilation via the anus, or EVA. The researchers were inspired not by turtles specifically but by loaches, freshwater fish that swallow air and absorb oxygen through their gut lining. The team demonstrated that delivering an oxygen-rich liquid form of perfluorocarbon, a compound already used in some clinical settings, into the rectums of mice and pigs improved blood oxygen levels and alleviated respiratory failure.¹⁰

The approach essentially repurposes the lower intestine as a supplementary breathing organ. The thin, highly vascularized wall of the gut, much like the lining of cloacal bursae in turtles, allows oxygen to pass into the bloodstream. The researchers concluded that EVA could potentially serve as a backup oxygenation method for patients in critical respiratory distress, offering a way to get oxygen into the blood when the lungs are failing.¹¹ The work is still early-stage and has not reached routine clinical use, but it shows how studying the unusual biology of aquatic animals can open up genuinely novel ideas in human medicine.

The parallel to turtle physiology is imperfect but real. Turtles evolved cloacal bursae over millions of years, optimizing a tissue surface for gas exchange that was originally designed for other purposes. The EVA approach does something conceptually similar in a clinical shortcut: it exploits an existing mammalian tissue, the rectal lining, that was never meant for breathing but happens to have the right physical properties. Both rely on the same basic biology: thin, well-supplied-with-blood tissue plus dissolved oxygen equals gas exchange. Evolution figured it out first.

Why the Fitzroy River Turtle Is the Star of This Story

Among the cloacal breathers, Rheodytes leukops occupies a special place. It was first described in 1980, lives only in the Fitzroy River system in Queensland, and is the most aquatically committed of the known cloacal-breathing turtles. Its bursae are proportionally enormous and covered in densely branching papillae that dramatically increase surface area for gas exchange.¹ While other species supplement their lung breathing with cloacal respiration, the Fitzroy River turtle has essentially reversed the priority: cloacal respiration is the default, and lung breathing is the backup.

This level of specialization has consequences. The species depends on clean, fast-flowing, well-oxygenated water. Anything that degrades water quality, slows flow, or reduces dissolved oxygen threatens its primary respiratory mechanism. The Fitzroy River turtle is classified as vulnerable in Queensland. Its extreme adaptation, the very thing that makes it biologically remarkable, also makes it fragile. A turtle that breathes mainly through its lungs can handle murky or low-oxygen water by simply surfacing more often. A turtle that breathes mainly through its cloaca does not have that easy fallback.

Researchers studying this species have tracked its heart rate and cloacal pumping behavior under varying oxygen conditions, finding that it fine-tunes both in response to how much oxygen is dissolved in the surrounding water.³ When oxygen is plentiful, the turtle pumps steadily and keeps its heart rate relatively stable. When oxygen drops, it slows its heart and adjusts its strategy to stretch out what oxygen is available. The precision of this regulation suggests that the cloacal respiratory system is not a crude workaround but a finely tuned physiological system that has been shaped by natural selection over a long period.

What People Get Wrong About Turtle Butt-Breathing

The biggest misconception is that all turtles do it. They do not. A box turtle in your backyard breathes exclusively with its lungs. A green sea turtle cruising a coral reef surfaces regularly to fill its lungs. Cloacal respiration is a specialized adaptation found in certain freshwater lineages, and the degree to which it matters varies even among those species.

A second common confusion is between cloacal breathing and the hibernation strategy of painted turtles. Popular accounts sometimes blend these together, as if painted turtles under the ice are breathing through their cloaca all winter. Painted turtles can absorb some oxygen through aquatic respiration when dissolved oxygen is available, but their famous overwintering trick is surviving without oxygen at all, relying on metabolic shutdown and shell buffering rather than on any form of breathing. The two stories are both about turtles staying alive underwater for long periods, but the mechanisms are fundamentally different.

A third misunderstanding is that cloacal respiration is somehow primitive or crude. The internal anatomy of the cloacal bursae in species like the Fitzroy River turtle is remarkably elaborate, with branching papillae that maximize surface area in a way that is functionally comparable to the gill filaments of a fish. The system is under active physiological control, with the turtle adjusting pumping frequency and heart rate to match conditions. Calling it “butt-breathing” is funny and not inaccurate, but it undersells the sophistication of what is actually happening.