In 1864, 34 living axolotls were brought from Mexico to Paris. They were the founder generation of a population of hundreds of thousands of axolotls raised in laboratories and zoos. Most axolotls in research laboratories around the world are descendants of the group brought to Paris in the 1860s. The animal is easy to breed in the laboratory, and it is the most commonly used salamander model organism in regeneration research. The axolotl genome has about 32 billion base pairs, which is ten times the size of the human genome. The population in laboratories is often very inbred, so it has little genetic diversity.

The axolotl is an amphibian and a type of salamander. It is sometimes called the Mexican walking fish, though it is not a fish at all. An axolotl lives in the water for its whole life. An axolotl has a tail with a fin. In the wild, an axolotl lives 10 to 15 years. An axolotl hides in mud and plants during the day and is active at night. Axolotls are neotenic, which means they keep juvenile characteristics into adulthood. They never go through metamorphosis and grow up to become adult salamanders. The tiger salamander is the closest relative of the axolotl. In experiments, axolotls have been forced through metamorphosis by adding iodine to their water.

Axolotls come from lakes and wetlands in southern Mexico City, in Mexico. According to some experts, axolotls descended from tiger salamanders and have lived in the middle of Mexico for only about the last 10,000 years. One idea is that they stay in the water because their native lakes never dry up. If so, they never had to trade water traits for land ones. They once lived in a series of lakes in the Mexican Central Valley. The Xochimilco-Chalco basin was once about 200 square kilometers of marshes, swamps and lagoons. It was greatly reduced when drainage projects were completed. Many of the lakes where they lived have been drained to reduce flooding.

Wild axolotls are mostly dark in color: black, brown or gray. An axolotl can reach about 12 inches long, and it weighs between 2 and 8 ounces. An axolotl has feathery gills on the outside of its head. Grown axolotls also have working lungs. They can breathe through their skin too. An axolotl eats worms, insect larvae and small fish. An axolotl catches its food by sucking it in. An axolotl communicates visually and chemically. It can also sense electrical impulses in the water to locate prey. A female axolotl lays her eggs on plants or rocks. The eggs hatch after about two weeks.

In an axolotl, a mass of cells called a blastema forms after an injury. It can grow back the missing part. An axolotl can grow back a lost leg in a few weeks to months. Axolotls heal wounds without forming scar tissue. Wound healing in a mammal leads to formation of scar tissue and does not progress to a blastema. Scarring prevents tissue from regenerating, so finding out how and why axolotls do not scar could unlock human tissue regeneration. Axolotls can also grow back limbs, hearts and parts of the brain. When an axolotl regrows a leg, every tissue is replaced, including skin, bone, cartilage and muscle.

Urbanization and pollution of their lakes are the biggest threats to them. Fish that were put into the waterways, such as tilapia and carp, compete with them for food and eat their young. As of November 2026, the IUCN Red List lists the axolotl as Critically Endangered. An IUCN assessment found only 50 to 1,000 left in the wild, and the number of wild axolotls is decreasing. The axolotl appears on Mexico's 50 peso banknote released in 2021. In 2025, scientists released 18 captive-bred axolotls into artificial wetlands near Mexico City. Farmers are now increasingly using traditional farming methods, free of pesticides and fertilizers, to help conserve axolotls.

Words to know

• neotenic: keeping young traits
• metamorphosis: big body change
• blastema: mass of cells
• inbred: closely related
• diversity: many kinds