Axolotls are amphibians that never grow out of the larval stage, so they remain aquatic for their whole life. As relatives of the on land living salamanders, they are famous for their regeneration ability which enables them to re-grow entire limbs and even portions of the brain and spine.

Axolotl   © Sophia Volzke

The name “Axolotl” comes from the Aztec language, “Nahuatl” of which the most commonly accepted translation is “water-dog”.

Australians and New Zealanders frequently refer to the Axolotl as the Mexican Walking Fish, though the Axolotl is not a fish but an amphibian, a salamander, part of the order Caudata/Urodela.
Their appearance is quite fascinating. Three pairs of external gill stalks (rami) originate behind their heads and are used to move oxygenated water. These are lined with filaments to increase surface area for gas exchange. Four gill slits lined with gill rakers are hidden underneath the external gills.

The Axolotl (Ambystoma mexicanum) exhibits the phenomenon known as neoteny.
Normally, amphibians like frogs and salamanders undergo metamorphosis from egg to larva, and finally to adult form. The Axolotl remains in its larval form throughout its whole life. This means that it retains its gills and fins, and it doesn’t develop the protruding eyes, eyelids and characteristics of other adult salamanders. It grows much larger than a normal larval salamander, and it reaches sexual maturity in this larval stage. Another term to describe this state is “perennibranchiate”. The animal is completely aquatic, and although it does possess rudimentary lungs, it breathes primarily through its gills and to a lesser extent, its skin.

Regeneration studies carried out around the world often involve the Axolotl.
Normal wound healing in animals occurs through the growth of scar tissue, which is not the same as the original tissue, nor is it as robust. Normal wound healing also does not allow for most animals to re-grow a lost limb. However the axolotl is fully capable of complete limb re-growth.
When a young axolotl that loses a foot to a sibling, it will usually grow it back over a period of a few weeks. This regeneration occurs via the formation of a “bud” at the end of the damaged appendage, followed by growth of the new foot.

The axolotl is only native to Lake Xochimilco and Lake Chalco in central Mexico. Unfortunately for the axolotl, Lake Chalco no longer exists as it was artificially drained to avoid periodic flooding, and Lake Xochimilco remains a diminished glimpse of its former self, existing mainly as canals.
As of 2010, wild axolotls are near extinction and it is possible that they might only exist in captivity and for research in the future.

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