The axolotl, scientifically known as Ambystoma mexicanum and popularly known as a Mexican walking fish, is a kind of a salamander related to the tiger salamander. The species was originally found in lakes such as Lake Xochimilco and Lake Chalco, underlying Mexico City. Axolotls in the wild are still found only in this area and this is where mexicanum and Mexican walking fish names are derived from.
Axolotls do not swim, rarely float and spend their entire lives walking along the water bottom. They are not fish and not regular salamanders either. So, are axolotls amphibians? Yes, they are. Axolotls are not fish but amphibians. Amphibians are ectothermic (organisms whose internal sources of heat are small or insignificant in controlling their body temperature), tetrapod vertebrates (possess four limbs) of the class Amphibia. Most species of this group are terrestrial or inhabit freshwater aquatic ecosystems. Amphibians start their development as larvae living in water but some species develop abilities to live outside this system, such as frogs, for example.
All of this perfectly describes why axolotls are amphibians – they are born as larvae to begin with. Interestingly enough, they never fully outgrow this condition and their unusual look is due to this phenomenon. They barely have any body temperature, prefer cool waters and do not enjoy bright and direct sunlight. They possess 4 limbs and inhabit fresh water ecosystems (were originally found in lakes). Finally, they never swim and leave the water they inhabit; therefore they cannot be classified as fish. All of these factors put together prove that axolotls are amphibians.
ARE AXOLOTLS AMPHIBIANS?
Yes, they are. Axolotls are a kind of salamander belonging to the family of amphibians.
WHY ARE AXOLOTLS CLASSIFIED AS AMPHIBIANS?
In order for a species to belong to the family of amphibians, it has to cover several requirements. After lengthy and in-depth scientific research, amphibians have been classified with several typical traits. Let’s take a closer look at them and see why axolotls are labeled as amphibians.
1. Amphibians Are Ectothermic.
All species belonging to the group of amphibians are ectothermic – meaning they are organisms in which internal physiological sources of heat are of relatively small or of negligible importance in controlling body temperature. Such organisms rely on environment heat sources. In other words, to explain it more simply, these organisms have from very low to zero body temperature and adapt in accordance to the environment they inhabit. Generally, however, they prefer cool, shady and damp places and like being inside or near water basins.
- How Do Axolotls Fit In This Criterion?
Axolotls NEVER leave the waters they inhabit. If you have one as a pet, it is recommendable to never take it out of the water, if possible.
Their body temperature is insignificant and they thrive in cooler waters rather than warm ones. The Mexican walking fish enjoys cool, damp and shady/dark places and do not like direct and bright sunlight. When you have one as a pet, you have to keep the aquarium in a shady place away from direct sunlight. The conclusion from this explanation is that axolotls perfectly respond to condition number one of amphibians – being ectothermal.
2. Amphibians Are Tetrapod Vertebrates.
Tetrapods are four-limbed (except snakes) animals. That means they have four limbs that allow them to move and use for different survival and mobility purposes. Tetrapods possess numerous anatomical and physiological features inherited from their aquatic ancestors such as the structure of the jaw, limb girdles and eyes and ears for seeing and hearing in water and air.
The group of vertebrates includes species such as tetrapods, including amphibians and reptiles.
- How Do Axolotls Fit in This Criterion?
Axolotls possess exactly four limbs which they use for walking on the water bottom.
3. Amphibians Inhabit Freshwater Aquatic Ecosystems.
Amphibians inhabit a wide variety of habitats, with most species living within terrestrial, fossorial, arboreal or freshwater aquatic systems. That is why amphibians usually start developing as larvae living in water. The young ones generally undergo metamorphosis from larva with gills to an adult with lungs. Amphibians use their skin as a secondary respiratory surface and some of them, such as salamanders, lack lungs and rely completely on their skin for breathing.
- How Do Axolotls Fit in This Criterion?
Axolotls were originally found in two Lakes – Chalco and Xochimilco in Mexico. Lakes contain fresh water and amphibians do inhabit freshwater aquatic systems. Axolotls in the wild are found only in these two lakes until today.
They remain larvae their entire lives, which distinguishes them from the rest of the amphibians. However, they do rely largely on their skin to breathe and very rarely show themselves on the surface to inhale air.
4. A Class Of Amphibians Is Caudata.
The order Caudata (a class of amphibians) gathers in itself salamanders – elongated, low-slung animals that resemble lizards. Also, they are more related to lizards than mammals and keep some larval characteristics as adults.
- How Do Axolotls Fit in This Criterion?
Axolotls are a kind of salamanders and respond fully to the description above – elongated, low-slung, resemble lizards and not so much mammals.
5. Functioning Of The Respiratory System.
The lungs of amphibians are primitive, if existing at all. There are a few internal septa (septum – separates adjacent alveoli in the lung system) and large alveoli. However, lungs are not of much use for amphibians – they exchange gasses (oxygen, including) through their skin.
- How Do Axolotls Fit in This Criterion?
Axolotls retain their larval state forever and have gills, instead of fully developed lungs. They rely mostly on their skin for breathing and survival and almost never float to the surface to inhale air.
WHY AXOLOTLS ARE NOT FISH?
As already mentioned axolotls never exit their larval shape and remain in it for the rest of their lives. That means they never leave water unlike other species that once grown up, they leave the water or can live both inside and outside of it. This is usually the case with amphibians and that is why they are called amphibians and not fish.
In very rare cases axolotls do grow up from their larval stage and leave the water to live on land. And because of these rare cases, they are not classified as fish but amphibians.
Finally, a curious fact to mention is that axolotls have the ability to regenerate. That means when a part of the tail or a limb is cut and lost, it grows back again. This ability is typical for some lizards, too. Regeneration has been a source of fascination to science for many years and its secrets have not been fully discovered yet.
SUMMARY
To sum up, let’s briefly go over all information about why axolotls are amphibians:
Amphibians are ectothermic (organisms whose internal sources of heat are small or insignificant in controlling their body temperature), tetrapod vertebrates of the class Amphibia. Most species inhabit freshwater aquatic ecosystems. Amphibians start their development as larvae living in water but some species have developed abilities to live outside this system. All of this perfectly describes why axolotls are amphibians – they are born as larvae to begin with. Interestingly enough, they never fully outgrow this condition and their unusual look is due to this. They barely have any body temperature, prefer cool waters and do not enjoy bright and direct sunlight. They possess 4 limbs and inhabit fresh water ecosystems (originally found in lakes).
All criteria for a species to be classified as amphibian can be collected in a couple of points:
1. Amphibians are ectothermic.
2. Amphibians are tetrapod vertebrates.
3. Amphibians inhabit freshwater aquatic ecosystems.
4. A class of amphibians is Caudata.
5. Function of the respiratory system.
Axolotls respond perfectly to all 5 points, which is more than enough to confidently classify them as amphibians.
