Have you ever wondered how some animals, like frogs and turtles, can stay underwater for a long time without drowning? Unlike humans, these amazing creatures have adapted in fascinating ways to be able to breathe both underwater and on land.
Keep reading to uncover the mysteries behind amphibious breathing!
If you’re short on time, here’s a quick answer to your question: Animals like frogs, turtles, aquatic mammals, and certain fish are able to breathe both underwater and on land because they have adaptations that allow them to extract oxygen from water or air.
They use gills, lungs, or a combination of both breathing systems.
Animals with gills
Fish
Fish are aquatic animals that possess gills to breathe underwater. There are over 30,000 known species of fish that inhabit oceans, rivers, lakes, and streams around the world. Fish obtain oxygen from water by passing it over their gills as it flows through the mouth and out the gill slits.
Gills are composed of filaments containing capillaries for gas exchange with the water. When water passes over the gills, dissolved oxygen moves into the bloodstream while carbon dioxide moves out. This allows fish to extract oxygen from water, which is about 1/20 as concentrated as oxygen in the atmosphere.
Amazingly, some fish can also absorb oxygen from air using adaptations that allow their gills to remain moist. Fish like betta fish and gouramis have a special organ called the labyrinth organ that allows them to breathe air.
The gills of fish are delicate structures that are highly adapted to extract oxygen from water. Fish gills are arranged in four pairs and are covered by an operculum or gill flap. Each gill arch contains two rows of gill filaments composed of cartilage.
The filaments contain secondary lamellae which increase the surface area for gas exchange. Between the filaments are tiny blood vessels that absorb oxygen as water passes over the gills. To ensure a constant flow of water, fish must keep swimming or moving their mouths to pump water through the gills.
This is why most fish will die from oxygen starvation if they stop moving for too long.
Fish have evolved amazing adaptations to survive in aquatic environments all over the world. Their gills allow them to thrive underwater by extracting oxygen even when it is scarce. Fish truly exemplify the diversity of respiratory systems in the animal kingdom.
Larval amphibians
Larval amphibians like tadpoles and salamander larvae breathe underwater using gills during their early life stages. Amphibians undergo metamorphosis, transitioning from aquatic gill-breathing larvae to air-breathing terrestrial adults.
Larval amphibians extract oxygen from water using external gills that protrude from the head and neck region. The feathery external gills increase surface area for gas exchange with the surrounding water. Oxygen diffuses into the bloodstream while carbon dioxide diffuses out.
Tadpoles have papery external gills that look like tiny leaves sprouting behind their heads. The gills are covered by gill slits that provide an opening for water to flow over the gills. As tadpoles mature, their lungs develop and their gills slowly disappear.
Salamander larvae have large external gills that extend from behind their heads in bushy tufts. They actively pump water through their gills using rhythmic movements of the throat. When salamander larvae transform into terrestrial juveniles, the gills are reabsorbed into the body.
The transition from gills to lungs allows amphibians to adapt from an aquatic lifestyle to living on land. While gills are ideal for extracting oxygen from water, lungs are more efficient for breathing air.
Larval amphibians exemplify the amazing metamorphosis that enables amphibians to inhabit both aquatic and terrestrial environments at different life stages.
Animals with lungs
Frogs
Frogs are amphibians that can breathe both underwater and on land using lungs. When under water, frogs rely on cutaneous gas exchange by diffusing oxygen through their moist skin. On land, frogs breathe with lungs like humans do. Their lungs allow them to take in oxygen and remove carbon dioxide.
A frog’s lungs are similar to human lungs in that they have alveoli – tiny sacs where gas exchange occurs. However, a frog’s lungs are much simpler and only have a single chamber compared to the complex, multi-chambered lungs of mammals.
Frogs don’t have a diaphragm or intercostal muscles to inflate their lungs. Instead, they use buccal pumping, forcing air into the lungs by contracting the throat.
When submerged underwater for extended periods, frogs rely on cutaneous respiration. Oxygen diffuses into the bloodstream through the moist lining of the mouth and skin. A frog’s skin is thin and permeable, containing many blood vessels close to the surface for gas exchange.
Some aquatic frog species have well-vascularized skin flaps to maximize cutaneous respiration.
Turtles
Like frogs, turtles are capable of breathing both in water and on land. Turtles have lungs to breathe air but can also exchange gases through their skin and the linings of their mouths and throats. This allows them to hibernate underwater for long periods.
When breathing air, turtles contract their throat and abdominal muscles to ventilate their lungs. Turtle lungs have broader surfaces containing thin blood vessel networks for gas exchange. Aquatic turtles have large shoulder muscles that let them actively pump water over the lining of their mouth and throat to facilitate cutaneous respiration.
Many turtle species have cloacal bursae, which are respiratory sacs connected to the cloaca. These sacs expand the surface area for gas exchange and oxygen absorption when under water. Some turtles can also extract a small amount of oxygen from water via the rich supply of blood vessels in their hindgut.
Aquatic mammals
Aquatic mammals like whales, dolphins, seals and sea lions breathe air using lungs. They must surface periodically to inhale oxygen from the atmosphere. Marine mammals have adapted in ways to maximize time spent under water in between breaths.
These adaptations include:
- Increased blood volume and concentration of red blood cells to store more oxygen.
- Ability to redirect blood flow away from non-essential organs when diving to conserve oxygen for the heart and brain.
- Excellent lung capacity and breath control to make the most of each inhale.
- Efficient respiratory systems that rapidly transfer oxygen to blood and remove carbon dioxide.
Additionally, many marine mammals like seals can collapse their lungs to expel air before diving deep. This prevents gases from entering the bloodstream and allows them to withstand water pressure changes better.
Overall, the remarkable lung adaptations of aquatic air-breathers let them thrive in both aquatic and terrestrial environments.
Animals with gills and lungs
Axolotls
Axolotls are fascinating amphibians that can breathe underwater using gills and on land using lungs. These unique salamanders are native to Lake Xochimilco in Mexico City. Axolotls have the amazing ability to regenerate limbs, organs, and even parts of their brain!
They can regrow lost legs, tails, jaws, and more with little difficulty. Axolotls stay in their larval form their whole lives, meaning they keep their tadpole-like features like gills and fins as adults.
When conditions get harsh, like cold weather or not enough food, axolotls can morph into a terrestrial form with lungs to survive on land. After metamorphosis, their gills disappear and they develop eyelids and a thicker skin.
See the axolotl’s incredible regeneration abilities on this National Geographic video. Though once abundant, axolotls are now critically endangered in the wild.
Mudpuppies
Mudpuppies, also called waterdogs, are types of salamander that retain their gills their entire lives. They have gray-blue skin, four toes on each foot, and bright red external gills on each side of their head. Mudpuppies can be over a foot long!
They inhabit lakes, rivers, and ponds across eastern North America. These fully aquatic salamanders rarely venture onto land, only leaving the water to migrate short distances. Though they have lungs, mudpuppies get the vast majority of their oxygen through their large, feathery gills which constantly wave back and forth.
Their gills allow them to stay underwater for their entire lives. Check out this video of a mudpuppy swimming with its gills fluttering. While mudpuppies have lungs, the lungs are small and not very well-developed.
If a mudpuppy is forced to rely on its lungs alone, it can quickly suffocate from lack of oxygen.
Lungfish
Lungfish are a unique group of freshwater fish that can survive out of water for extended periods using primitive lungs. There are only six species of lungfish left in the world, inhabiting rivers and lakes in South America, Africa, and Australia.
Fossil records show lungfish have remained unchanged for over 300 million years. All lungfish species have lungs connected to their mouth via a glottis. Their lungs are very similar to the lungs of amphibians and other primitive vertebrates.
While the lungfish’s gills are its primary breathing apparatus underwater, if the water dries up during droughts, the lungfish can gulp air at the surface into its lungs. Some species can even burrow into the mud and breathe air through their lungs for up to four years while waiting for water to return!
The Australian lungfish has the most advanced lungs and largest genome of all lungfish, making it the closest living fish relative to the tetrapods, or four-limbed vertebrates. Learn more in this overview from the American Museum of Natural History.
How gills work
Gills are the specialized respiratory organs that allow certain animals, like fish and amphibians, to extract oxygen from water. They are a marvel of evolution that enable aquatic creatures to thrive underwater. Here’s an overview of how these unique structures work:
Gill anatomy
Gills are made up of filaments and lamellae. The filaments are the main shafts that contain blood vessels for gas exchange. Attached to the filaments are tiny plate-like lamellae. These lamellae provide a huge surface area to allow for diffusion of oxygen from the water into, and carbon dioxide out of, the bloodstream.
The process
As water flows over the gills, dissolved oxygen moves across the thin membranes of the lamellae by diffusion down a concentration gradient into the blood capillaries. At the same time, carbon dioxide diffuses out of the blood into the water.
This countercurrent exchange between the capillaries and water is extremely efficient.
The deoxygenated blood in the blood vessels then flows toward the heart, where it will be pumped to the gills again to pick up more oxygen. This forms a continuous circuit to keep tissues supplied with oxygen.
Special adaptations
Different species have specialized gill adaptations to enhance oxygen uptake. For example:
- Some fish can open or close their operculum (the gill cover) to adjust water flow for more efficient gas exchange.
- Sharks have multiple gill slits on the side of their body to maximize diffusion surface area.
- Tuna have countercurrent blood flow within the lamellae for rapid gas exchange.
How lungs work
The lungs are incredible organs that allow animals to breathe both underwater and on land. Here’s a look at how they work their magic:
Gas exchange
The main job of the lungs is to exchange gases between the air and the blood. When we breathe in, oxygen enters the lungs and passes through the thin walls of the air sacs called alveoli. It then binds to red blood cells for transport around the body.
At the same time, carbon dioxide waste exits the blood and makes its way out of the lungs when we exhale.
Breathing mechanisms
Animals like frogs and turtles can breathe through their skin when underwater, but they still need lungs for breathing air. Marine mammals like seals and sea lions also have lungs to breathe when on land. Their lungs work just like ours – inhaling oxygen and exhaling carbon dioxide.
The difference is they can hold their breath for a really long time while diving and swimming!
Underwater extraction
You might wonder how animals can extract oxygen from water using their lungs. Some species have developed anatomical adaptations that allow their lungs to extract dissolved oxygen from water rather than air:
- Sea snakes have a special valve that closes off their nostril cavity on land, opening only when they are underwater.
- Sea turtles can pull oxygen from water into their lung tissues through a process called cloacal respiration.
- Crocodiles have specialize multi-chambered lungs with the ability to shunt blood away from non-functioning areas of the lung when underwater.
So while mammal lungs are fairly similar to ours, reptiles have developed some cool tricks for breathing in aquatic environments!
Conclusion
The ability to breathe both underwater and on land gives amphibious animals great flexibility to move between aquatic and terrestrial habitats. Evolution has produced specialized respiratory systems like gills and lungs that enable gas exchange in different environments.
Understanding the anatomy behind amphibious breathing continues to fascinate biologists and nature lovers alike.
