Scientific classification
Species: mexicanum
Binomial nomenclature
Ambystoma mexicanum Shaw

The Axolotl (Ambystoma mexicanum, the colloquial Mexican walking fish) is an aquatic salamander.

It is noted for its appearance and its demonstration of neoteny, remaining in its aquatic larval form even as a sexually-mature adult, and not undergoing metamorphosis.

A fully grown axolotl, at age 18-24 months, ranges in length from 150-450 mm, although a size close to 230 mm is most common and greater than 300 mm is rare. They have distinctive 'fern-like' gill structures that are not covered (as are gills in fish and in frog tadpoles); axolotls also breathe through the skin and possess lungs. In colour they range from albino or white to black, through greys, tans and browns. Wild axolotls are rarely white, and the albino mutant common in labs and pet stores was created in an American laboratory in the 1950s. The axolotl is carnivorous, consuming small prey such as insects and small fish, which are swallowed whole.

Axolotls are very closely related to Tiger Salamanders (Ambystoma tigrinum), and would probably better be considered a subspecies of tiger salamander than a separate species. Axolotls can metamorphose, although they do so rarely, and in the metamorphosed condition they resemble Ambystoma mavortium, a relative of the tiger salamander.

Native only to Lake Xochimilco and Lake Chalco in central Mexico, the wild population has been put under heavy pressure by the growth of Mexico City. It is currently listed by CITES as an endangered species. In the Spanish language it is called the Salamandra ajolote.

The axolotl is used in research and large numbers are bred in captivity. The feature of the salamander that attracts most attention is its healing: the axolotl does not heal by scarring and is capable of regenerating entire lost appendages and, in certain cases, more vital structures. Another attractive feature, for research, is the large and robust embryos.

The name is from the Aztec Nahuatl language.

Pop cultural reference: The word "axolotl" is used frequently in crossword puzzles. It was often used in the early years of Mad Magazine as a running joke.