The concept of “breathing through the butt” refers to a biological process known as cloacal respiration. The cloaca itself is a single, multi-purpose opening found in certain animal groups, including reptiles and birds, that functions as the exit point for the digestive, urinary, and reproductive tracts. While this orifice is primarily used for waste and reproduction, some aquatic species have evolved to utilize it for a highly specialized form of gas exchange. This adaptation allows them to remain submerged for extended periods.
Identifying the Aquatic Respiration Specialists
The animal most famously associated with this unique ability is the Fitzroy River Turtle (Rheodytes leukops), a freshwater species native exclusively to the Fitzroy River basin in Queensland, Australia. This turtle has perfected cloacal respiration to such an extent that it can derive a significant portion of its oxygen needs from the water. Under normal conditions, this species can absorb up to two-thirds of its required oxygen through this method, with some reports suggesting they can remain underwater for up to three weeks at a time. Other Australian river turtles, such as the Mary River turtle and the white-throated snapping turtle, also use this adaptation to a lesser degree. Beyond reptiles, certain aquatic insects, like the nymphs of dragonflies, use a similar form of rectal respiration, drawing water into their hindgut for oxygen absorption.
The Mechanism of Cloacal Respiration
The physical process of cloacal respiration involves specialized anatomical structures located within the cloaca. Inside the turtle’s posterior opening are two large, sac-like extensions called cloacal bursae, which function like aquatic lungs. These bursae are lined with numerous tiny, finger-like projections known as papillae, which greatly increase the surface area available for gas exchange. The papillae are densely packed with blood vessels, creating a thin membrane between the water and the turtle’s bloodstream. The turtle actively pumps water in and out of the cloaca through rhythmic muscular contractions, circulating the oxygen-rich water over the vascularized papillae, allowing dissolved oxygen to diffuse directly into the blood and carbon dioxide to be released into the water.
Why This Adaptation is Necessary
This respiratory method provides a significant survival advantage for the Fitzroy River Turtle. The ability to extract oxygen from the water allows the turtle to remain submerged for extended durations, which is beneficial for avoiding aerial and terrestrial predators. Staying underwater for long periods also enables the turtle to maintain its position in fast-flowing currents without needing to expend energy swimming to the surface for air. Cloacal respiration is especially important when the water temperature is low, such as during periods of dormancy or brumation. Colder water holds more dissolved oxygen, and the turtle’s metabolic needs decrease, allowing the cloacal exchange to sufficiently support the animal’s lowered oxygen demand.