A neotenic salamander, closely related to the Tiger Salamander. Larvae of this species fail to undergo metamorphosis, so the adults remain aquatic and gilled. It is also called ajolote (which is also a common name for different types of salamander). . Axolotls are used extensively in scientific research due to their ability to regenerate limbs. Axolotls should not be confused with waterdogs, the larval stage of the closely related Tiger Salamanders (Ambystoma tigrinum and Ambystoma mavortium), which are widespread in much of North America and also occasionally become neotenic, nor with mudpuppies (Necturus spp.), fully aquatic salamanders which are not closely related to the axolotl but bear a superficial resemblance. As of 2010, wild axolotls are near extinction due to urbanization in Mexico City and polluted waters. Nonnative fish such as African tilapia and Asian carp have also recently been introduced to the waters. These new fish have been eating the axolotls' young, as well as its primary source of food. The axolotl is currently on the International Union for Conservation of Nature's annual Red List of threatened species. This is a leucistic specimen.
The axolotl is only native to Lake Xochimilco and Lake Chalco in central Mexico. Unfortunately for the axolotl, Lake Chalco no longer exists as it was artificially drained to avoid periodic flooding, and Lake Xochimilco remains a diminished glimpse of its former self, existing mainly as canals. The water temperature in Xochimilco rarely rises above 20 °C (68 °F), though it may fall to 6 or 7 °C (45 °F) in the winter, and perhaps lower. The wild population has been put under heavy pressure by the growth of Mexico City. Axolotls are also sold as food in Mexican markets and were a staple in the Aztec diet. They are currently listed by CITES as an endangered species and by IUCN as critically endangered in the wild, with a decreasing population.
Axolotls exhibit a property called neoteny, meaning that they reach sexual maturity without undergoing metamorphosis. Many species within the axolotl's genus are either entirely neotenic or have neotenic populations. In the axolotl, metamorphic failure is caused by a lack of thyroid stimulating hormone, which is used to induce the thyroid to produce thyroxine in transforming salamanders. The genes responsible for neoteny in laboratory animals may have been identified; however, they are not linked in wild populations, suggesting artificial selection is the cause of complete neoteny in laboratory and pet axolotls. Taken at the Vancouver Aquarium.