The axolotl is sometimes called the Mexican walking fish, though it is not a fish at all. It is an amphibian and a type of salamander, and its closest relative is the tiger salamander. An axolotl lives in the water for its whole life. Axolotls are neotenic, which means they keep juvenile characteristics into adulthood, and they never go through metamorphosis and grow up to become adult salamanders. One idea is that axolotls stay in the water because their native lakes never dry up, so they never had to trade water traits for land ones. According to some experts, axolotls descended from tiger salamanders and have lived in central Mexico for only about the last 10,000 years. Wild axolotls are mostly dark in color. They hide in mud and plants during the day and are active at night. An axolotl can reach about 12 inches long, and it weighs between 2 and 8 ounces.
Lazzaro Spallanzani (1729-1799) investigated salamander regeneration by amputating salamander tails and limbs. In 1864, 34 living axolotls were brought from Mexico to Paris, and in 1867 Auguste Duméril, a French herpetologist at the natural history museum in Paris, published the first scientific papers on regeneration in the Mexican axolotl. The word axolotl comes from Nahuatl, a language of the Aztecs. The first living axolotls that came to Europe in 1864 were the founder generation of a population of hundreds of thousands of axolotls bred in laboratories and zoos, and most axolotls in research labs around the world are descendants of the group brought to Paris in the 1860s. The axolotl is easy to breed in the laboratory. It is the most commonly used salamander model organism in regeneration research. Axolotls are a common research subject for biologists because of their regrowing ability. The population in labs is often very inbred, so it has little genetic diversity.
An axolotl has feathery gills on the outside of its head for breathing underwater, and adult axolotls have working lungs as well as gills. Axolotls can also breathe through their skin. An axolotl has a tail with a fin and small, underdeveloped teeth. An axolotl eats worms, insect larvae and small fish, and it catches food by sucking it in. It may suck up gravel, which helps grind up its food. Wild axolotls live 10 to 15 years. A female axolotl lays her eggs on plants or rocks, and she can lay up to about a thousand eggs. The eggs hatch after about two weeks, and young axolotls get no parental care.
An axolotl can regrow a lost leg in a few weeks to months, and it can also regrow hearts and parts of the brain. Within hours after an amputation, a wound epithelium covers the severed edge of the limb. In days, the wound epithelium becomes innervated and turns into a signaling center called the apical epithelial cap. Blastema formation requires an adequate nerve supply. Blastema cells with positional information interact with each other and with stump cells so that regenerated tissues reform in the right place. As of November 2026, a 2025 study suggests that a particular enzyme and gene work with retinoic acid to grow the right body part in the right spot. A tiger salamander regenerates a limb in 155 to 180 days, while a juvenile axolotl takes approximately 40 to 50 days.
When immune cells called macrophages were removed, salamanders lost their ability to regenerate a limb and instead formed scar tissue. Limb stumps that failed to regenerate without macrophages regained full regenerative capacity when amputated again after macrophage populations were replenished. Wound healing in a mammal leads to formation of scar tissue and does not progress to a blastema, while in axolotls wound healing eventually restores normal skin architecture rather than forming a scar. Scarring prevents tissue from regenerating, so finding out how and why axolotls do not scar could unlock human tissue regeneration. Genes that direct the growth of organs and limbs during development are silenced in adult people, but in axolotls they may be activated again after an injury.
In the wild, axolotls come from lakes and wetlands in southern Mexico City, in Mexico, and they once lived in a series of lakes in the Mexican Central Valley. Many of those lakes have been drained to reduce flooding. Urbanization and pollution of their lakes are the biggest threats to axolotls. Fish put into the waterways, such as tilapia and carp, compete with axolotls for food and eat their young, and storks, herons and large fish sometimes eat axolotls. As of November 2026, the IUCN Red List lists the axolotl as Critically Endangered. An IUCN assessment found only 50 to 1,000 axolotls left in the wild, and the number of wild axolotls is decreasing. In 2025, scientists released 18 captive-bred axolotls into artificial wetlands near Mexico City. Farmers are increasingly using traditional farming methods, free of pesticides and fertilizers, to help conserve axolotls.
Words to know
- neotenic: keeping young traits
- blastema: mass of cells
- macrophages: immune cells
- epithelium: covering layer
- inbred: closely related
