[1] These lakes were drained by Spanish settlers after the conquest of the Aztec Empire, leading to the destruction of much of the axolotl's natural habitat.

As of 2020[update], the axolotl was near extinction[6][7] due to urbanization in Mexico City and consequent water pollution, as well as the introduction of invasive species such as tilapia and perch.

[11] Axolotls may be confused with the larval stage of the closely related tiger salamander (A. tigrinum), which are widespread in much of North America and occasionally become paedomorphic, or with mudpuppies (Necturus spp.

Axolotls possess features typical of salamander larvae, including external gills and a caudal fin extending from behind the head to the vent.

Males are identified by their swollen cloacae lined with papillae, while females are noticeable for their wider bodies full of eggs.

In addition, there is wide individual variability in the size, frequency, and intensity of the gold speckling, and at least one variant develops a black and white piebald appearance upon reaching maturity.

[18] Axolotls also have some limited ability to alter their color to provide better camouflage by changing the relative size and thickness of their melanophores.

They are especially easy to breed compared to other salamanders in their family, which are rarely captive-bred due to the demands of terrestrial life.

One attractive feature for research is the large and easily manipulated embryo, which allows viewing of the full development of a vertebrate.

[18] The feature of the axolotl that attracts most attention is its healing ability: the axolotl does not heal by scarring and is capable of the regeneration of entire lost appendages in a period of months, and, in certain cases, more vital structures, such as tail, limb, central nervous system, and tissues of the eye and heart.

In some cases, axolotls have been known to repair a damaged limb, as well as regenerating an additional one, ending up with an extra appendage that makes them attractive to pet owners as a novelty.

It is believed that during limb generation, axolotls have a different system to regulate their internal macrophage level and suppress inflammation, as scarring prevents proper healing and regeneration.

[33] The axolotl's regenerative properties leave the species as the perfect model to study the process of stem cells and its own neoteny feature.

The newer technologies of germline modification and transgenesis are better suited for live imaging the regenerative processes that occur for axolotls.

[40] In the absence of induced metamorphosis, larval axolotls start absorbing iodide into their thyroid glands at 30 days postfertilization.

These include increased muscle tone in limbs, the absorption of gills and fins into the body, the development of eyelids, and a reduction in the skin's permeability to water, allowing the axolotl to stay more easily hydrated when on land.

[47] Six adult axolotls (including a leucistic specimen) were shipped from Mexico City to the Jardin des Plantes in Paris in 1863.

[citation needed] Vilem Laufberger in Prague used thyroid hormone injections to induce an axolotl to grow into a terrestrial adult salamander.

Sirens and Necturus are other neotenic salamanders, although unlike axolotls, they cannot be induced to metamorphose by an injection of iodine or thyroxine hormone.

Neoteny has been observed in all salamander families in which it seems to be a survival mechanism, in aquatic environments only of mountain and hill, with little food and, in particular, with little iodine.

In this way, salamanders can reproduce and survive in the form of a smaller larval stage, which is aquatic and requires a lower quality and quantity of food compared to the big adult, which is terrestrial.

If the salamander larvae ingest a sufficient amount of iodine, directly or indirectly through cannibalism, they quickly begin metamorphosis and transform into bigger terrestrial adults, with higher dietary requirements.

Water quality tests reveal a low nitrogen-phosphorus ratio and a high concentration of chlorophyll a, which are indicative of an oxygen-poor environment that is not well-suited for axolotls.

[51] Another factor that threatens the native axolotl population is the introduction of invasive species such as the Nile tilapia and common carp.

These invasive fish species threaten axolotl populations by eating their eggs or young and by out-competing them for natural resources.

This lack of genetic diversity can be dangerous for the remaining population, causing an increase in inbreeding and a decrease in general fitness and adaptive potential.

The offspring produced after bottleneck events have a greater risk of showing decreased fitness and are often less capable of adaptation down the line.

Studies have shown that captive-bred axolotls that are raised in a semi-natural environment can catch prey, survive in the wild, and have moderate success in escaping predators.

These captive-bred individuals can be introduced into unpolluted bodies of water or back into Lake Xochimilco to establish or re-establish a wild population.

[61] In captivity, axolotls eat a variety of readily available foods, including trout and salmon pellets, frozen or live bloodworms, earthworms, and waxworms.