Axolotl

The axolotl (Ambystoma mexicanum) is a species of mole salamander that stays fully aquatic for its whole life. Adults keep obvious external gills, a wide head, lidless eyes and a fin running along the back and tail. Their limbs look small and underdeveloped, with long, thin digits.

A sexually mature adult, at around 18 to 27 months, ranges from 15 to 45 cm long. About 23 cm is most common and anything over 30 cm is rare. Axolotls keep growing throughout their lives.

The natural colour is brown or tan with gold speckles and an olive undertone. Common colour variants include leucistic (pale pink body, black eyes), xanthic (grey body), albinistic (pale pink or white body, red eyes) and melanistic (black or dark blue body). Axolotls are kept in home aquariums, zoos and public aquariums, and are used widely in scientific research.

Axolotls originally lived in a system of connected lakes and wetlands in the highlands of Mexico, including Xochimilco and Chalco. The name comes from a Nahuatl word, and the animal is linked to Xolotl, an Aztec god. Wild axolotls are now critically endangered, with the habitat mostly lost to the growth of Mexico City.

They belong to the same genus as the tiger salamander, and their closest relative in the family is the Eastern tiger salamander.

In 1863 a shipment of 34 adult axolotls was sent from Mexico City to the Jardin des Plantes in Paris. Thousands of captive-bred animals were then distributed around Europe for scientific research. Most axolotls under human care today descend from a single group of fewer than 36 individuals, and they differ genetically from the wild population.

As aquarium technology developed, axolotls became common exhibits and an occasional pet in home aquariums.

Axolotls spend most of their time at the bottom of their tanks. They are carnivores and find food by smell, snapping at a likely meal and sucking it in with vacuum force.

Their gills are used to move oxygenated water, and they can also gulp air from the surface to supply their lungs. In the wild they eat small prey such as worms, molluscs, aquatic insects, crayfish and small fish, and sometimes other salamanders.

They are neotenic, meaning they reach sexual maturity without going through metamorphosis, so they keep their gills and live in water all their lives. In the wild, introduced fish have made axolotls less active as they try to avoid being eaten.

Axolotls in captivity are prone to gastrointestinal blockage. They tend to swallow bedding material along with food, and bowel obstruction is described as a common cause of death in laboratory axolotls.

Temperature matters because they are poikilothermic. Cooler water slows the metabolism and reduces appetite, while water above 24 C can raise the metabolic rate and cause stress and eventually death. Chlorine, commonly found in tap water, is harmful to them.

Their healing ability is remarkable. Rather than scarring, they regenerate tissue, and lost limbs and tail can regrow over months. In certain cases they can also regrow tissues of the eye and heart, and even non-vital parts of the brain. This ability declines with age but does not disappear completely.

In the wild, axolotls live between 10 and 15 years. Axolotls also show resistance to the fungus that causes chytridiomycosis in many amphibians.

This is general awareness only, not veterinary advice. Always consult a vet about your pet's health.

What is an axolotl?

It is a species of mole salamander that never undergoes metamorphosis in normal life. It stays aquatic and keeps its external gills as an adult.

How big do axolotls get?

Adults range from 15 to 45 cm, with around 23 cm most common. Anything over 30 cm is rare.

What colours do axolotls come in?

The wild type is brown or tan with gold speckles. Pet colours include leucistic, xanthic, albinistic and melanistic, and breeders often cross them. White or pink animals with pink eyes are common in the pet trade.

Can an axolotl turn into a land salamander?

Not naturally. Metamorphosis can be triggered artificially with thyroid hormones, but among hobbyists this can result in death, so it is generally discouraged.

Can axolotls regrow body parts?

Yes. They can regrow limbs and tails, and in certain cases tissues of the eye and heart and non-vital parts of the brain.

The axolotl genome, published in 2018, was the largest animal genome completed at that time. It is about ten times the size of the human genome.

Sometimes an axolotl repairs a damaged limb and also grows an extra one, which makes them attractive to some owners as a novelty.

Axolotls have barely visible vestigial teeth and feed mainly by suction.

An axolotl appears on Mexico's 50-peso banknote, issued in 2021, and became the official emoji of Mexico City in 2017. In Japan they are known as wooper loopers, and the Pokemon Wooper is based on one.