Amphibians undergo numerous metamorphic changes, many of which concern their respiratory systems. Since frogs spend part of their lives on land and in water, many amphibian enthusiasts wonder if frogs have gills for breathing underwater.
Frogs have gills as tadpoles during the first 20 weeks of their lives when they primarily live in water. However, frogs lose their gills as they transform into froglets and prepare to live on land. As adults, frogs have no gills and use their lungs and permeable skin for breathing.
While tadpoles use gills for breathing, they do not retain their gills for long as their gills are only suitable for their early life stages. Join us as we discuss how frogs develop gills during their formative phases and lose their gills as they transition to life on land.
Frog Tadpoles Have Gills
Once fertilized frog eggs transform into tadpoles, otherwise known as polliwogs, they breathe through their gills. Frog tadpoles are fully aquatic during their initial metamorphic stages, and more sophisticated respiratory systems only start developing after a few weeks.
As a result, tadpoles have gills that they use to breathe underwater, and their gills are their primary respiratory organ during this metamorphic stage. Tadpoles’ gills undergo a few metamorphic changes before they finally transition to complete respiratory systems as they become mature and semi-aquatic frogs.
Frog tadpoles generally have external gills when they emerge from developed zygotes which are visible on the outside. External gills also function as primary mucosal surfaces in tadpoles, as these creatures have not yet developed the skin and other organs used as mucosal surfaces in adult frogs.
Internal gills are formed when the external gills become concealed by an additional layer of skin, formally referred to as an operculum. This layer of skin creates an opercular chamber around the gills, and spiracles vent the gills.
Depending on the frog species, the spiracles used to vent the gills may occur in the following formations:
- Two spiracles on both sides of the tadpole’s body
- A single spiracle on the left side of the body
- A single spiracle near the vent on the underside
Countless mitochondria-rich cells (MR cells) are scattered on the lateral and ventral epithelia of the internal gill arches and tufts. These cells help the overall transition of ions, which assists the respiration process for tadpoles.
Tadpoles typically develop internal gills during their early phases. The transition from external to internal gills is one of the first metamorphic changes experienced by tadpoles during the formative phases along with the development of their legs.
However, it should be noted that external gills may be present for longer timeframes within some frog species as there are over 7,400 known frogs, some with different development processes.
When Do Frogs Lose Their Gills?
Tadpoles only need their gills to breathe during their fully aquatic phase, and their gills are slowly replaced by sophisticated respiratory components as they transition into the froglet phase. Most frog tadpoles lose their gills after approximately 20 to 25 weeks. However, some froglets may retain their gills for longer timeframes.
The gills used by tadpoles will be replaced by the components necessary for breathing on land as they become froglets. They generally develop lungs and permeable skin tissue which is useful for gas exchange through the skin and mouth lining membranes.
Some young froglets have lungs and gills for a time, as they cannot rely solely on either system during this state. Their gills will only disappear once the tadpoles become complete froglets, ready to spend more time on land (CTNF). Froglets will still typically remain on land for shorter timeframes compared to semi-aquatic adults.
After this point, frogs use their lungs, skin to breathe, depending on the context and environmental conditions.
Below is an outline of how frog tadpoles lose their gills over time:
|Stage||Gill Development||Time Frame||Habitat|
|Early Tadpole||External gills||3 Days||Aquatic|
|Mid-Tadpole||Internal gills||6 weeks||Aquatic|
|Late Tadpole||Lungs being to develop||14 to 16 weeks||Semi-aquatic|
|Froglet||Lungs developing||6 to 9 weeks||Semi-aquatic|
|Adult Frog||Fully developed lungs||–||Species-dependent|
Frogs do not have gills, as they spend more time on land once they reach adulthood. Frogs typically return to water bodies for specific purposes or timeframes, such as mating seasons. Some frog types, such as aquatic frogs, generally spend more time in water compared to others. However, they too utilize other breathing methods while underwater.
Adult Frogs Do Not Have Gills
Since frogs are equipped with a wide range of unique and efficient bodily components, they still have the means to breathe underwater despite their lack of gills. Frogs have three primary surfaces to exchange oxygen and carbon dioxide during respiration, which proves useful whether on land or underwater.
|Skin Membranes||Gas Exchange||Frogs’ skin is permeable, containing a large number of blood vessels. Gas can be exchanged through the skin’s thin membraneous tissue.||Useful underground, underwater, or on land. The skin can absorb oxygen from surroundings, including humid air, water, and soil.|
|Mouth Lining||Gas Exchange||Gas exchange can occur readily within the mouth lining.||Predominant breathing method when at rest on land.|
|Lungs||Oxygen is Forced Into Lungs Through Mouth and Nostril Movements||Frogs lower the floor of the mouth and open their nostrils, after which they close the mouth to force air into the lungs. Carbon dioxide is released by moving up the mouth floor to push air out of the nostrils.||When surrounded by air on land, and when more oxygen is demanded by the body.|
Frogs typically use their skin, mouths, and lungs in combination, and their permeable skin is the primary component that allows frogs to breathe underwater without gills. These components are only present in adult frogs, and tadpoles have gills until they develop the necessary respiratory features for living on land and in water.
More About Frog Gills
Although frog tadpoles are equipped with functional gills, these features are only suited for their formative phases. As tadpoles grow and become froglets, they lose their gills and develop more sophisticated respiratory systems suited for living on land and in water bodies.
Learn more about how frogs breathe on our blog:
Uchiyama M, Yoshizawa H. Salinity tolerance and structure of external and internal gills in tadpoles of the crab-eating frog, Rana cancrivora. Cell Tissue Res. 1992 Jan;267(1):35-44. doi: 10.1007/BF00318689. PMID: 1735117.