The Axolotl (Ambystoma mexicanum), also known as the Mexican Walking Fish, is actually a salamander – a class of amphibians originating in the northern hemisphere. They come in many colour varieties, including the traditional wild type (brown, grey or almost black, with dark spots), albino (golden with pink eyes), leucistic (white with black eyes), melanoid (absence of iridescent pigment and very little yellow), axanthic (lacking iridescent and yellow pigment), and any combination of these, such as white albino (white with pink eyes), or melanoid albino (white with almost invisible yellow spots and no shiny pigment). The Axolotl was originally native to two freshwater lakes south of Mexico City – Xochimilco and Chalco, Sadly, Chalco is now gone, and Xochimilco survives only as a network of canals and lagoons. These bodies of water are muddy bottomed and rich in plant and animal life.
The Axolotl exhibits the phenomenon known as neoteny. Ordinarily, amphibians undergo metamorphosis from egg to larva (the tadpole of a frog is a larva), and finally to adult form. The Axolotl, along with a number of other amphibians, remains in its larval form throughout its life. In other words 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.
- Tank size – a 60 x 30 x 37 cm (24 x 12 x 15 inches) aquarium is adequate for two adults. Water depth is not important, but 15 cm (6 inches) or more is recommended.
- Substrate – an aquarium bare of substrate, while perhaps less attractive, is safest and generally easier to clean. If you choose to have substrate, use either sand or pebbles/gravel that are too large to swallow.
- Water temperature – keep it between 14 and 22°C (57 to 72°F). Any temperature over 25°C (77°F) is unsuitable for anything more than a few days. High temperatures stress axolotls, and anorexia, fungal and bacterial infections often result.
- Filtration is essential, but axolotls are stressed by flowing water, so make sure that the water flow from a power filter, for example, is reduced or diffused in such a way as to prevent large volumes of water flowing about the tank at speed.
- Plants are not essential, unless breeding is planned. In any case, either choose robust plant species or those easily replaced, because axolotls tend to dredge up and damage delicate plants in their tank.
- Hiding places, though not essential, are a good idea – axolotls seem to like to have the option to hide at times
- Remember to ensure water quality is maintained by making regular water changes – 20% or so every two weeks is usually adequate unless large numbers are being kept in a small tank or over feeding is taking place. Remember to treat tap water with a water conditioner prior to use as it may contain harmful substances such as chlorine, chloramine, metals.
Axolotls are voracious feeders. They are carnivores, requiring a meat-based diet. They have rather rudimentary teeth, designed for gripping rather than biting or tearing. As a result, their food is generally swallowed whole, so anything they want to eat must fit into their mouths.They will eat earthworms, tubifex worms (live, frozen, or freeze-dried – sometimes incorrectly labelled as “bloodworms”), actual bloodworms (the larvae of chironomid midges), blackworms (an aquatic relative of earthworms), crustaceans (shrimp), pieces of fish (avoid salted fish and marine fish), strips of beef heart or other lean red meat, and small invertebrates like insects, tadpoles and feeder fish. The last two should probably be avoided because they often harbour parasites, and these can be passed on to the axolotls. Most axolotls will also eat the sinking pellets sold commercially to feed trout and salmon. These are an excellent food. Food that floats should not be used, as axolotls feed on the floor of their tank. They empty their mouth of water, then suddenly opening it very wide, sucking in everything in the immediate vicinity – food or substrate. The warmer the axolotls are kept, the more regularly they should be fed. As much food as they will eat in 15 minutes is a good guide. If kept at 22°C (72°F) they should only require feeding every two to three days. Don’t leave food to spoil the water after feeding.