Toads are amphibians, which means they spend part of their lives in water and part on land. During the breeding season, it is common to see hundreds of toads migrating to ponds where they can swim and lay their eggs. But can toads breathe underwater?
Toads can breathe underwater via cutaneous respiration. Dissolved oxygen in the water that comes in contact with their skin is absorbed into the bloodstream via diffusion, and carbon dioxide is released from the bloodstream into the water.
However, this method of breathing does not give them all the oxygen they need, so they can only be underwater for a limited time before they have to resurface to breathe air with their lungs.
Toad Tadpoles Can Breathe Underwater With Their Gills
Most toads start their lives as tiny tadpoles. Tadpoles are very different from adult toads because they’re adapted for a fully aquatic life (life in the water), while adult toads are adapted for a mostly terrestrial life.
Toad tadpoles have gills on either side of their head, and a flat paddle-like tail fin to help them move in the water.
At this stage, toad tadpoles breathe underwater through their gills, just like fish.
Their gills have an extensive capillary network very close to the skin surface; Oxygen that is dissolved in the water that comes in contact with their gills is absorbed into their bloodstream via diffusion.
At the same time, carbon dioxide from the bloodstream passes through the gills and is diffused into the water.
Sometimes, Toad Tadpoles Breathe Air
Tadpoles sometimes live in water with low oxygen levels – where their gills (and skin) cannot absorb sufficient oxygen. This means they also need to breathe air. For this reason, most toad tadpole species also develop lungs in addition to their gills.
When they first hatch, the tadpoles are too feeble to break through the water’s surface for a gulp of air. To get around this, they “bubble-suck”.
To do this, they first stick their open mouths to the underside of the water’s surface. They then open their jaws wide and suck at the water’s surface. Doing this creates an air pocket that they can pinch off by quickly closing their jaws.
After they close their mouth, a portion of the fresh air bubble is forced down into their lungs.
Since the tadpoles are tiny, they usually cannot absorb the entire air bubble, and the excess is burped out as a small bubble, after which it floats back up to the water’s surface.
Once the tadpoles get bigger, they will be strong enough to break through the water’s surface for a gulp of air.
Tadpoles Transform Into Toadlets
After a period of 2 to 3 weeks to as long as over 3 months (depending on the species), the tadpoles go through a process known as metamorphosis. In this process, they lose the features that help them live in the water and develop features more suitable for living on land.
During this process;
- They lose their gills and get well-developed lungs for breathing air
- The tail shortens and is eventually absorbed into the body
- They develop strong legs for moving on land
Once this process is complete, tiny toadlets (small toads), typically half an inch long will leave the water and live a fully terrestrial life.
These toadlets will grow into adult toads and once they mature, they will go back to the water to breed and lay their eggs.
Adult Toads Breathe Underwater Through Their Skin
Adult toads have well-developed lungs which they use to breathe air. They take air through their nostrils, and down into their lungs.
That said, amphibian lungs are quite primitive when compared to our own. They usually can not give a toad all the oxygen it needs.
For this reason, toads also have the ability to breathe through their skin and thin membranes in their mouth and throat to get extra oxygen.
The skin contains a large network of capillaries and other blood vessels close to the surface. The oxygen that comes in contact with their skin and membranes is absorbed into the bloodstream via diffusion.
At the same time, carbon dioxide from the bloodstream passes through the skin and membranes and is diffused into the atmosphere.
This process of “skin breathing” known as cutaneous respiration is very similar to what happens inside our lungs.
How Toads Breathe Underwater
Toads breathe underwater via cutaneous respiration. Dissolved oxygen in the water that comes in contact with their skin is absorbed into the bloodstream via diffusion. At the same time, carbon dioxide from the bloodstream passes through the skin and is diffused into the water.
However, this method of breathing does not give them all the oxygen they need, so they can only be underwater for a limited time before they have to resurface to breathe air with their lungs.
How Long Can Toads Stay Underwater?
Exactly how long a toad can stay underwater depends on how much oxygen it needs vs how much oxygen it can absorb from the water through its skin.
This is usually affected by: how much dissolved oxygen there is in the water, the temperature, and how active the toad is
1. How Much Oxygen There Is in the Water
Fast-moving or ‘stirred up’ water generally contains more oxygen than still water. This is because oxygen from the atmosphere mixes with the water more easily.
If water is very still, oxygen only dissolves on the water’s surface, and anything below the upper layer of the water will have a low oxygen content.
Additionally, aquatic plants and algae also affect the dissolved oxygen in a body of water. During the daylight hours, they produce oxygen through photosynthesis and release it into the water.
At night, aquatic plants and algae will use up dissolved oxygen in the water via aerobic respiration and release carbon dioxide into the water.
For these reasons, the concentrations of dissolved oxygen in water with lots of photosynthesizing aquatic vegetation will be highest in the mid-to-late afternoon when photosynthesis rates are greatest and will reach the lowest concentrations just before the sun rises the next morning.
Also, water with lots of decaying plants will have a lower oxygen content. This is because the bacteria responsible for the process of decomposition use oxygen and release carbon dioxide into the water, reducing the oxygen content of the water.
Toads can stay underwater in water with a high oxygen content for much longer than they can in water with a low oxygen content.
2. The Temperature
Toads are ectothermic (cold-blooded) animals, so the environmental temperatures will affect their rate of metabolism. At higher temperatures, they will have a higher metabolic rate, meaning they have a greater oxygen demand.
At lower temperatures, the opposite is true. Toads will have a lower metabolic rate meaning they have a lower oxygen demand.
Also, the temperature will affect the oxygen content of the water. More oxygen will dissolve into the water at colder temperatures, than at warmer temperatures.
This means toads can stay underwater at lower temperatures for much longer than they can at warmer temperatures.
3. How Active the Toad Is
Activity affects how much oxygen the body needs. Think about it, when we are running or jogging, we breathe heavier and in much quicker breaths than when we are lying on the couch.
For toads, this is also true. They will have a higher oxygen demand when they are very active in the water (escaping a predator for example), and a lower oxygen demand when they are inactive.
For this reason, toads will be able to stay underwater when at rest for much longer than when they are active.
Can Toads Drown?
Even with their ability to breathe underwater through their skin, toads can drown. Toads have lungs, and If their lungs fill with water, they can drown.
The oxygen they absorb through their skin is usually not enough to meet all their oxygen needs for long, so they can only stay submerged for a limited time before they will have to surface to breathe air with their lungs.
If a toad dives into the water so deep that it can not surface for air in time, it will drown.
Final Thoughts
Toads are semi-aquatic animals, which means they spend part of their lives on land, and part in the water. They start their lives as tadpoles with gills for breathing underwater. At this stage of their life, frogs (tadpoles) can stay underwater for as long as they can get enough oxygen through their gills.
Over time, the tadpoles will transform into toadlets through the process of metamorphosis. During this process, they lose their gills and develop functional lungs.
Once fully transformed, the toadlets will leave the water for life on land. Adult toads breathe by using their lungs and absorbing oxygen through their skin and thin membranes in their mouths and throats.
When underwater, they breathe entirely by absorbing dissolved oxygen in the water through their skin.
This does usually not meet all their oxygen requirements, so they can only stay underwater for a limited amount of time before they have to surface to breathe.