The turtles that breathe through their butts
Australia's Fitzroy River turtle has a highly unusual survival hack: it can breathe through its rear end. Using a process called cloacal respiration, the turtle pumps water in and out of its cloaca—the multi-purpose opening used for waste and reproduction. Specialized chambers inside are lined with blood vessels that extract oxygen directly from the water, allowing the turtle to remain submerged for up to three weeks.
The Mechanics of Rear-End Respiration
While all freshwater turtles possess lungs and must periodically surface to inhale atmospheric air, the Fitzroy River turtle (Rheodytes leukops) has developed a remarkable supplementary mechanism that minimizes its need to surface. This adaptation is known as cloacal respiration. The cloaca is an all-purpose chamber found in reptiles, birds, and amphibians that serves the digestive, excretory, and reproductive systems. In this species, however, the interior of the cloacal opening houses an intricate respiratory apparatus consisting of two enlarged internal sacs called cloacal bursae.
These bursae are not simple cavities. Their internal surfaces are densely carpeted with highly vascularized, multi-branched projections known as papillae. By rhythmically expanding and contracting muscles in the pelvic region, the turtle actively pumps water in and out of the cloaca at rates ranging between 15 and 60 times per minute. As water flushes over the papillae, dissolved oxygen diffuses directly across the thin epithelial walls and into the surrounding network of capillaries. This physiological exchange mirrors the basic function of aquatic gills, enabling the turtle to absorb the majority of its resting oxygen requirements directly from the surrounding water.
Under optimal aquatic conditions, cloacal respiration allows the Fitzroy River turtle to remain submerged for extended durations without taking a single breath of air at the surface. Laboratory observations and field records indicate that individuals can stay completely underwater for days or even weeks at a time. This continuous submersion offers substantial ecological advantages, drastically reducing the turtle's exposure to surface predators like birds of prey and terrestrial hunters while conserving energy that would otherwise be spent swimming to the surface.