The Axolotl(/ˈæksəlɒtəl/; from Classical Nahuatl: āxōlōtl [aːˈʃoːloːtɬ] (listen)), Ambystoma mexicanum, also known as the Mexican walking fish, is a neotenic salamander related to the tiger salamander. Although colloquially known as a “walking fish“, the axolotl is not a fish but an amphibian.
Axolotls should not be confused with waterdogs, the larval stage of the closely related tiger salamanders (A. tigrinum and A. mavortium), which are widespread in much of North America and occasionally become neotenic.
As of 2010, wild axolotls were near extinction due to urbanization in Mexico City and consequent water pollution, as well as the introduction of invasive species such as tilapia and perch. They are listed as critically endangered in the wild, with a decreasing population, by the International Union for Conservation of Nature and Natural Resources (IUCN) and as an endangered species by the IUCN’s CITES treaty. Axolotls are used extensively in scientific research due to their ability to regenerate limbs. Axolotls were also sold as food in Mexican markets and were a staple in the Aztec diet.
Like all ambystomatids, they are extremely loyal to their birthplaces, and will travel long distances to reach them. However, a single tiger salamander has only a 50% chance of breeding more than once in its lifetime. The tiger salamander’s ideal breeding period is somewhere between the late winter and early spring, once the ground is warm enough and the water is thawed. Males nudge a willing female to initiate mating, and then deposit a spermatophore on the lake bottom. About 48 hours after insemination, the female is ready to deposit her eggs in the breeding pool. She carefully attaches the eggs to secure twigs, grass, and leaves at the bottom of the pool to ensure her eggs safety. In about 12–15 days time, the eggs will be fully hatched and ready to mature in the pool. It takes a tiger salamander approximately 3 months to reach full maturity and leave the breeding pool. Large-scale captive breeding of tiger salamanders has not been accomplished, for unknown reasons.
Limbs are fully developed within a short time of hatching. Some larvae, especially in seasonal pools and in the north, may metamorphose as soon as feasible. These are known as small morph adults. Other larvae, especially in ancestral pools and warmer climates, may not metamorphose until fully adult size.
Some populations may not metamorphose at all, and become sexually mature while in their larval form. These are the neotenes, and are particularly common where terrestrial conditions are poor.