The strangest fish in all of Mexico – the axolotl – isn’t actually a fish at all, but that’s just the least of Ambystoma mexicanum’s issues
The extremely strange Mexican walking fish, or axolotl, seems plagued with problems. For a start, there is the confusion over its name – it’s not a fish at all, but a rare type of salamander which, for a number of reasons, seems to have been caught in an evolutionary dead end.
Its natural habitat was formerly limited to two high-altitude lakes in Mexico – Lake Xochimilco, and Lake Chalco – both of which were drained by settlers following the Spanish conquest of the Aztec civilisation during the early part of the 16th Century.
Today, Lake Chalco has completely disappeared under Mexico City’s extensive urban sprawl, and not much is left of Lake Xochimilco save for a few polluted canals. The existence of axolotl in the habitats that were left to them was further threatened by the introduction of invasive species, the end result of which has left the Mexican walking fish treading a fine line along the edge of extinction.
Not surprisingly, the axolotl is on the CITES list of endangered species, and is currently listed on the IUCN Red List of Threatened Species as Critically Endangered. The last assessment in 2019 estimated there might be as many as 1,000 individuals left in the world – or as few as just 50.
Some might say that the omens surrounding A. mexicanum‘s fate had long ago been foretold – centuries ago when it was plentiful and abundant, the axolotl was considered a delicacy by Aztec gourmets and is thought to be named after their god for deformity and death – Xolotl.
Like other salamanders, the axolotl is an amphibian, but unlike its relatives, it has evolved as a solely aquatic beast due to a phenomenon known as neoteny, in which the animal remains stuck in the larval stage and doesn’t develop functioning lungs as it matures.
Neoteny is considered by some to be a backward step in evolutionary terms and its cause is much debated – but in salamanders, it may be a survival mechanism, as reaching sexual maturity while remaining small in body size may help the species survive and reproduce in food-scarce environments.
The axolotl has had one fortuitous spin of the evolutionary dice, as it can regrow damaged limbs and other tissues, which has fascinated scientists for many years as the ability to regenerate body parts in humans would be the greatest biotechnological game-changer of all time.
On the downside to this good fortune, however, is the fact that it has a large and easy-to-experiment-on embryo, which effectively means the axolotl has been saved from total extinction just to become a staple of research in labs around the world.