The axolotl (scientific name: Ambystoma Mexicanum), also known as the Mexican Walking Fish, is a type of salamander species native to high-altitude lakes near Mexico City, Mexico, North America.
For decades, their cute looks have made axolotls very popular amongst exotic pet enthusiasts. In parallel, their amazing biology – such as their ability to regenerate limbs – has caused them to become the subject of intense scientific scrutiny and research.
More recently, appearances in blockbuster franchises like Pokémon (via a character called Wooper) or Minecraft have significantly boosted the salamander’s popularity amongst younger generations – spurring a renewed interest in keeping pet axolotls.
Unfortunately, their numbers in the wild have been dwindling and axolotls are now listed as a critically endangered species by the International Union for Conservation of Nature and Natural Resources (IUCN).
In this article we will do a brief overview of axolotls, then we will take a look at the main factors contributing to the decline in axolotl populations and finally, we will see what efforts are being made to protect the species.
Table of Contents
- Overview
- How Many Axolotls Are Left?
- Main Contributing Factors To The Extinction Of Axolotls
- Actions Taken To Help Protect Axolotls
Overview
The axolotl, known by the scientific name Ambystoma Mexicanum, is a paedomorphic salamander related to the tiger salamander and one of the world’s most famous lissamphibians.
Scientific Classification Of The Axolotl
Axolotls are a type of amphibian. The class Amphibia is divided into three orders: Anura (frogs & toads), Gymnophiona (caecilians), and Caudata (salamanders, newts & sirens) – to which axolotls belong.
- Kingdom: Animalia
- Phylum: Chordata
- Class: Amphibia
- Order: Caudata
- Family: Ambystomatidae
- Genus: Ambystoma
- Species: Ambystoma Mexicanum
Historical Origins Of The Axolotl
Axolotls In Aztec Mythology
The Aztecs were an indigenous nomadic American people who populated northern Mexico. In the 13th century, they eventually settled on a handful of islands in Lake Texcoco in the Tenochtitlan basin, where they founded the town of Tenochtitlán (which now corresponds to modern-day Mexico City).
In the lake, they discovered a large salamander and called the salamander “axolotl” after Xolotl, the Aztec god of fire and lightning. Xolotl was a rebel god who transformed himself into an axolotl to escape being sacrificed at the hands of his fellow deities. Legend has it that he was ultimately found, captured, and killed.
Axolotls have been part of Aztec, and by extension Mexican folklore, culture, and history for centuries. Many Mexicans feel that the decline in the number of wild axolotls is also a threat to the survival of Mexican culture and history.
The Axolotl’s Native Habitat
The axolotl’s native habitat is the high-altitude, cold-water lakes of Chalco and Xochimilco, in the Tenochtitlan basin, near Mexico City.
From the Aztec era onwards, Lake Chalco was drained to avoid flooding and to reclaim land for the expansion of Mexico City.
As of 2022, only Lake Xochimilco remains, albeit in a much reduced and depleted form compared to its former glory.
Historically, a key characteristic of these high-altitude lakes was the purity and temperature of the water. Indeed, the water temperature rarely rose above 68 degrees Fahrenheit or 20 degrees Celsius. During winter months, water temperatures can reach as low as 42 degrees Fahrenheit or 6 degrees Celsius.
It’s believed that these conditions are thought to favor neoteny, one of the axolotl’s defining features.
Scientific Interest In Axolotls
The axolotl became an immediate hit with European scientists when it was taken from Mexico to Paris, in 1864.
In particular, 18th-century scientists were amazed by – and focused their research on – two of the axolotl’s many amazing characteristics: neoteny and regenerative ability.
In today’s day and age, modern gene sequencing technologies are used to understand what makes the axolotl genome so special.
Axolotls Are Neotenic
Neoteny is defined by the reaching of sexual maturity without undergoing metamorphosis.
In other words, a neotenic species reaches sexual maturity without losing certain embryonic or larval features.
The axolotl is neotenic. It reaches adulthood as early as 6 months old and as late as 24 months old, yet retains a number of juvenile features such as its external gills or long tadpole-like dorsal fin. Unlike other salamanders, axolotls also spend their entire lives living underwater.
It’s believed that the failure to metamorphose is caused by the absence of a thyroid-stimulating hormone to induce the thyroid to produce thyroxine, a catalyst for metamorphosis in other salamander species.
Axolotls Can Regenerate
Another fascinating characteristic of the axolotl is its ability to regenerate. Axolotls are thought to be the only vertebrate that is able to regrow an extremity.
However, axolotls can regrow more than just their limbs.
As a matter of fact, axolotls can regenerate almost any part of their bodies including vital organs like their heart, reproductive organs such as their testes, or even parts of their central nervous system such as their spinal cord or parts of their brain!
It’s easy to see why scientists, and in particular those in the medical field, would be interested in understanding what gives the salamander these amazing abilities, and if there may be a way to mimic these properties in humans.
However, it’s also worth noting that scientific interest in axolotls is thankfully not what is nowadays causing their populations to decline in the wild. Indeed, a majority if not all of the axolotls studied in laboratories now come from breeding programs, where axolotls are bred in captivity.
Popularity As Exotic Pets
The popularity of axolotls in the scientific community is only rivaled by the love and attention they garner among exotic pet enthusiasts.
Indeed, the adorable axolotl has become a firm favorite with exotic pet owners. It’s worth noting however that just as is the case with axolotls used for scientific research, the axolotls sold as pets on the open market are for the vast majority bred in captivity.
How Many Axolotls Are Left?
The number of axolotls left corresponds to the number of axolotls left in the wild, and the number of axolotls kept in captivity – either as pets or for scientific research.
How Many Axolotls Are Left In The Wild?
Based on a number of different studies, it is estimated that there are now less than 1000 adult axolotls left in the wild.
How Many Axolotls Are Left In Captivity?
Based on a guesstimate, the number of axolotls left in captivity – i.e. axolotls kept as pets and axolotls bred for scientific and medical research – is in the hundreds of thousands.
How Many Axolotls Are Left In The World?
Based on a guesstimate, the total number of axolotls left in the world – i.e. all the axolotls left in the wild and all the axolotls kept in captivity – could be in the hundreds of thousands.
The threat of extinction of this critically endangered animal is dangerously near. But what are the causes of this threat? What is killing the axolotl?
Main Contributing Factors To The Extinction Of Axolotls
There are four main factors causing the population decline of the amphibians – polluted water, loss of habitat, overfishing, and the introduction of invasive species.
As with any being, the threat of extinction exists due to factors such as natural selection.
Water Pollution
The first and perhaps the main cause of the decline in the number of axolotls is water pollution. Pollution is becoming increasingly hard to control and manage as the climate changes and our actions within the world do not change to help. Over the years we have lost vast parts of the axolotl’s habitat, due to polluted waters becoming inhospitable for the creatures to live in.
Axolotls are found in a lake near Mexico called ‘Xochimilco’. This lake has been a victim of increased pollution as the city of Mexico increases and the population expands. This lake is the home of Mexicos ‘floating gardens’ which is an attraction for visitors, however, has also led to the increase of waste and non-degradable objects to find their way into the water, polluting it.
This human intervention has caused the waters to become toxic and fewer and fewer creatures can live in them. This means that more and more parts of the lake are not suitable for the axolotls to live in, reducing their habitat and thus reducing their numbers. If there is no clear and clean water for these creatures to live and breed, then their population will continue to decline.
Within recent years, some biologists have introduced what they call ‘pens’ in an attempt to save the species. These ‘pens’ are areas of the lake that have been placed in strategic positions in order to protect the axolotl from any of the threats that they or their habitat may face.
These ‘pens’ are portions of the lake where the water is not as affected by pollution and are habitable for the axolotls to live in.
Destruction Of Natural Habitat
Years ago, axolotls could also be found in a lake known as ‘Lake Chalco’, alongside lake Xochimilco. Chalco was one of their prime historical habitats, however, the lake has been drained and no longer exists. Xochimilco has also had large parts of it drained.
This is mostly down to overflooding. Because the lakes would overflow, they had to be drained so they wouldn’t pose a threat to people and our structures. And though that threat was diminished, the threat of extinction for the axolotls was created.
Because there are now fewer places where the species can live and breed, there are fewer of them.
They do not have the space to expand their numbers and increase their population size. Because the only lake that they now are found in has also become somewhat of a ‘tourist attraction’, the areas that the creatures can live in have been dramatically reduced.
This, and the factor of polluted water, has caused the little waters left to be non-habitable for the axolotls, and they are struggling to survive. `
Overfishing For Human Consumption
If water pollution and loss of habitat weren’t enough for these poor creatures, the axolotl is also viewed as a delicacy.
They are actively fished so that they can be supplied locally and exported as this represents a source of food and also income for certain locals.
This is a problem because it doesn’t give the species a chance to live and breed and expand their population size – not without being hunted and eaten first.
Introduction Of Invasive Species
From Predator To Prey
The last main cause of the decline of this animal is the introduction of new invasive species, which rank higher in the food chain and predate on axolotls.
Historically, the axolotl was the highest in the food chain found in the Mexican lakes where they live. However, the introduction of invasive species has caused our amphibian friends to drop lower on down on the food chain.
Invasive fish such as carp, perch, and tilapia were introduced into the axolotl’s habitat and have been eating into the local axolotl population, causing their numbers to dwindle.
These predatorial fish were introduced in the 1970s through a food program with the aim of adding more protein into local diets. Although the program was helpful and successful for the locals in terms of providing them with more sources of protein, it also had an unintended negative consequence as scientists hadn’t foreseen that these non-native fishes would prey on axolotls.
In particular, axolotls are most vulnerable to these larger fish when they are still eggs or juveniles.
This means that when they have grown into adults they are less likely to be eaten; however, the number of axolotls that reach adulthood is declining every day. Because the invasive species eat the babies before they have a chance to grow, the chance for the axolotls population to increase is hindered. The fewer babies there are, the fewer adults for they to grow into.
In short – these cute smilers have become a food source for everyone – humans and fish alike.
Competition For Food
Additionally, the introduction of these new species has put pressure on the quantity of food available to axolotl populations.
Indeed, axolotls are carnivores and live off a diet of worms, tadpoles, and other small fish.
Prior to the arrival of competitors, they had most of these food sources for themselves. However, tilapia and perch also happen to eat these food sources – and have been competing with axolotls for them.
This, in turn, has also put pressure on axolotls and caused their population to decline.
Inbreeding In Captivity
Each of these factors has made a huge contribution as to why the axolotl species have become critically endangered.
In fact, there are now more axolotls in pet shops and laboratories than there are in the wild.
Their breeding for pets and for scientific research may help prevent the species from going extinct in captivity, but it isn’t going to help when it comes to finding these creatures in their natural habitat.
It may also contribute to the in-breeding of the species, meaning that their genetic makeup will weaken due to pet-stores breeding relatives with each other.
When this happens, the babies of this process are more likely to have defective genetic material and are more susceptible to disease and premature death.
Basically, this means, that they are being bred with close relatives meaning that they will have a different set of genes to wild axolotls. This is a problem because if all the axolotls left have been bred through the same genes, they could be more likely to be wiped out fully through diseases that they cannot combat – and in large populations.
While this means it is unlikely that the species will ever become fully extinct as they can be preserved and saved through captivity, it is highly likely that they are going to be lost from the natural world. It is not enough simply to have captive populations of this species.
They need to exist naturally in the wild, where they are exposed to natural selection, to continue to mutate genes, strengthen their gene pool and preserve their species.
Thankfully, attempts and plans are being put in place to save the natural habitat of the species, and grow their numbers in the wild once again.
Actions Taken To Help Protect Axolotls
In light of the threat axolotls are facing, a number of actions have been taken in order to help protect the species.
Classification Of Axolotls On The IUCN Red List
Whilst axolotls had been classed as Rare in the wild since 1986 by the International Union for Conservation of Nature and Natural Resources (IUCN), their status was downgraded to Vulnerable in 1996, and they ultimately became listed as Critically Endangered on the IUCN Red List in 2006.
The International Union for Conservation of Nature’s Red List of Threatened Species, established in 1964, is the world’s most comprehensive source of information on the global conservation status of animals, plant species, and fungi. It provides information about population size, location, habitat, ecology, international trade & consumption of species, threats, and conservation actions.
The IUCN Red List acts as a barometer of world biodiversity health and has become widely relied critical to protect the Earth’s natural resources by informing decision-making and policy and catalyzing action around biodiversity conservation.
The Critically Endangered classification of the axolotl’s plight has helped raise awareness around the issue and has been a positive catalyst for change and a driver behind a number of conservation programs to help save and protect the species.
Classification Of Axolotls On Appendix II Of CITES
Axolotls are also listed under Appendix II of the Convention on International Trade in Endangered Species (CITES).
CITES is an international agreement between governments that aims to ensure the survival of certain species of wild animals and plants by protecting them from the negative effects linked to international trade thereof.
As a result, the international trade of wild axolotls is heavily regulated and monitored.
Axolotl Conservation & Breeding Programs
To help restore axolotl populations in their native habitat, a number of conservation and breeding programs have been put in place over the years.
One such program initiated by Dr. Luis Zambrano of Mexico’s National Autonomous University and a handful of other researchers and students includes positioning filters on the canals leading into lake Xochimilco to prevent predatory fish from invading axolotl habitat.
In parallel, lab-bred axolotls are regularly released into the axolotl’s native habitat. The aim is to drive wild axolotl numbers up once again and help the species disseminate its genetic material into the wild.