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The axolotl ( ; from Classical Nahuatl: āxōlōtl ; Ambystoma mexicanum) is a species of mole salamander.

It is neotenic, reaching sexual maturity without undergoing metamorphosis, and the adults remain fully aquatic with obvious external gills. Axolotls may be difficult to distinguish from the larval stage of other neotenic adult mole salamanders, in particular the tiger salamander, or other species such as mudpuppies. Axolotls originally inhabited a system of interconnected wetlands and lakes in the highlands of Mexico. They were known to inhabit the smaller lakes of Xochimilco and Chalco and are presumed to have inhabited the larger lakes of Texcoco and Zumpango. The desiccation of these lakes, initiated by the Aztecs and accelerated during the 20th century, has led to the destruction of much of the axolotl's natural habitat, an area now largely occupied by Mexico City. Wild axolotls have been driven to near extinction by the introduction of invasive species such as tilapia and carp; with a decreasing population of around 50 to 1,000 adult individuals, the species has been assessed as critically endangered by the International Union for Conservation of Nature (IUCN) and is listed under Appendix II of the Convention on International Trade in Endangered Species (CITES). There currently exists a large captive population of axolotls, with specimens used extensively in scientific research because of their unusual ability to regenerate body parts, including limbs, gills and parts of their eyes and brains. The species is also used as a model organism. As aquarium technology has developed, axolotls have become a common exhibit in zoos and public aquariums, as well as an occasional pet in home aquariums. The axolotl is a popular subject in contemporary culture, inspiring a number of works and characters in the media.

The term "axolotl" is a Nahuatl word which has been translated variably as "water slave", "water servant", "water sprite", "water player", "water monstrosity", "water twin", or "water dog". Some sources prefer the term "Mexican axolotl" to refer to this species unambiguously, as "axolotl" may be used for unmetamorphosed individuals of other Ambystoma species, although the word is most commonly used to refer to wild A. mexicanum and captive individuals.

A sexually mature adult axolotl, at age 18–27 months, ranges in length from 15 to 45 cm (6 to 18 in); a size close to 23 cm (9 in) is most common, and any greater than 30 cm (12 in) is rare.

The axolotl is unusual in that it has a lack of the thyroid-stimulating hormone that triggers the thyroid to produce thyroxine, which is needed for metamorphosis to take place; instead, the axolotl keeps its gills and lives in water all its life, even after becoming an adult and able to reproduce.

The axolotl is native to the freshwater lakes of Xochimilco and Chalco in the Valley of Mexico (though the species may have also once inhabited the larger Lakes of Texcoco and Zumpango).

The wild axolotl is thought to reach sexual maturity at 1.5 years of age, with a generation length of around 5.5 years. The life expectancy of a wild axolotl is between 10 and 15 years.

Unaware of their neoteny, French zoologist Auguste Duméril was surprised when, instead of the axolotl, he found in the vivarium a new species, similar to the salamander. In Prague, the Czech medical doctor Vilém Laufberger used thyroid hormone injections to induce an axolotl to grow into a terrestrial adult salamander.

The axolotl is also considered an ideal animal model for the study of neural tube closure due to the similarities between human and axolotl neural plate and tube formation; the axolotl's neural tube, unlike that of a frog, is not hidden under a layer of superficial epithelium.

In 1999, the video games Pokémon Gold and Silver, made by Japanese developer Game Freak, introduced a Pokémon named Wooper, which is directly based on an axolotl.

Quick Facts

• Some sources prefer the term "Mexican axolotl" to refer to this species unambiguously, as "axolotl" may be used for unmetamorphosed individuals of other Ambystoma species, although the word is most commonly used to refer to wild A. mexicanum and captive individuals.
• There currently exists a large captive population of axolotls, with specimens used extensively in scientific research because of their unusual ability to regenerate body parts, including limbs, gills and parts of their eyes and brains.
• Axolotls may be difficult to distinguish from the larval stage of other neotenic adult mole salamanders, in particular the tiger salamander, or other species such as mudpuppies.
• The species is also used as a model organism.
• A sexually mature adult axolotl, at age 18–27 months, ranges in length from 15 to 45 cm (6 to 18 in); a size close to 23 cm (9 in) is most common, and any greater than 30 cm (12 in) is rare.

Source material: Wikipedia - "Axolotl". Adapted and summarized for DiscoverScroll. Original contributors are credited through the linked Wikipedia article. Read original on Wikipedia. CC BY-SA 4.0. Changes were made from the original.