Axolotl - Ambystoma mexicanum
By Jessie M Sanders, DVM, CertAqV
Although not technically a fish, the Axolotl (Ambystoma mexicanum) is an extraordinarily unique amphibian. Nicknamed the Mexican Walking Fish, the Axolotl was first discovered in Lake Xochimilco in Mexico in the 19th century by French explorers. These alien-like salamanders have a distinctive appearance. While most salamanders progress through an aquatic stage of their life cycle before becoming land-dwelling animals, the Axolotl remains in this adolescent-like stage and remains 100% aquatic.
Their unique appearance has made them desirable pets for many years. This has led to them being natively endangered and trade-restricted by CITES, which means they cannot be taken from the wild. However, Axolotls have an active breeding program, the majority currently undertaken at the University of Kentucky, which has reared hundreds of generations of captive-bred Axolotls.
It should be cautioned that the Axolotl is certainly not a beginner pet. If you have never kept aquatic pets before, it is highly recommended that you do NOT start with Axolotls. A basic, tropical freshwater fish tank is a great starting point for any aquatic hobbyist. Once you have mastered the care and maintenance of a basic freshwater setup, you may progress towards Axolotls.
While they may need more care and consideration than some other aquatic species, these unique and personable animals make excellent pets and can become much beloved family members.
The adolescent form is characterized by frilly gills sticking out on both sides of the neck. Axolotls do have lungs, however, that are fully functional, and often they will rise to the surface for a gulp of air. Axolotls reach maturity around one year of age and can top out at 30 cm in length. Females are usually larger than males and will increase significantly in girth during egg production.
Their skin can be seen in different color varieties. The wild-type Axolotl appearance is mostly brown with a mottled mix of black, yellow, and iridescent spots. Captive Axolotls have been bred to show only one-color variety of skin pigment, rather than the mix of colors their wild counterparts display. Melanoid (dark) adults lack the mottled skin appearance and are a dark color throughout their body. White or albino Axolotls lack melanin, instead expressing yellow and iridescent pigments.
In addition to their unique appearance, one of the most astonishing characteristics Axolotls have is their healing and regenerative abilities. At the site of any injury, or even amputation, the surrounding cellular structure will revert to its embryonic state and regrow the affected tissue. This makes Axolotl skin very unique in its ability to heal from nicks and cuts without any scarring. This ability to regrow limbs with amazing ease is extremely rare throughout the entire animal kingdom. In fact, this regenerative capacity has been long studied in order to try to manipulate other animal, and even human tissue to behave similarly.
Axolotl Diet & Feeding
Find a good quality Axolotl diet or be ready with some live food options. An Axolotl’s diet can consist of live food or soft pellets, but keep in mind that live food may try to bite your Axolotl and cause skin lesions or skin irritation. If your Axolotl is accustomed to live food, remember to be patient when transitioning from live food to pellets. There are commercial diets available that will support optimum health.
It is best to feed your Axolotl small meals throughout the day, rather than one big meal; gorging themselves at one meal, which they have a tendency to do, will cause digestive problems. Keep to a consistent schedule and feed at the same spot in your aquarium. With patience, Axolotls can be trained to accept pellets at a target or in a specific area of your tank.
Axolotl Health Concerns
The most common issues with Axolotls come from their aquatic environment. Unlike most fish, amphibians do not have a protective scaly coat. This makes their skin more prone to nicks and tears. Even with their amazing healing abilities, Axolotls also have to protect their delicate external gills. Make sure that all your aquarium décor has no sharp edges and remove anything that your Axolotls are getting stuck under or struggling to move around.
Juvenile Axolotls are prone to accumulating air in their abdomens. Air leads to a distended abdomen and to floating upside-down. This occurs due to their immature gut adapting to a higher protein diet. This syndrome will correct itself with time as the animal matures, but reducing portion size can have more immediate resolution. Never try to “burp” the air out of your Axolotl.
Another floating syndrome can be caused by small tears in the lungs, allowing air to be free elsewhere in the body. Your veterinarian will need to take radiographs, commonly known as x-rays, to determine the location of the air.
Axolotls are most susceptible to various skin diseases. The most common cause of skin lesions and blisters is poor water quality. It is highly recommended that you purchase a water quality test kit and test your water regularly with any aquatic animal. They are also susceptible to external skin parasites, which are easily diagnosed by microscopic examination of the skin. As with other skin issues, skin parasites are often secondary to poor water quality.
Another causative factor behind skin blisters is Ambystoma tigrinum virus (ATV). This virus is fatal. Once a diagnosis has been established, steps need to be taken to protect the other Axolotls from disease spread. Unfortunately, the only resolution is early euthanasia of the infected animal, along with complete cleaning of any infected habitat systems with bleach or complete replacement of all habitat supplies.
With clean water, a good home, and complete diet, you can expect up to 15 years with your Axolotl.
Building an Axolotl Habitat
It is recommended to start with one Axolotl in a 10-gallon tank. If you have used the tank as a terrarium or other land-based system previously, make sure to clean it thoroughly with bleach and rinse it very well.
Multiple Axolotls housed together will require their own territory. While they are peaceful animals, and both genders cohabitate well with each other, there may be occasional nips, accidental bites, or breeding scuffles in a tank environment. Adding caves, which can be as simple as PVC pipes of appropriate size, along with soft plants or large rocks, will provide a safe space for each animal. No more than three Axolotls can be kept in a 10-gallon tank.
Axolotls require brackish water — a mix between fresh and salt water. This is one of the main reasons that Axolotls are not recommended for first-time aquatic pet owners. It is recommended that owners be very familiar and comfortable with basic freshwater aquariums before starting with Axolotls.
A specialized Axolotl water recipe is necessary for optimal health. One well-known solution, mixed by German Axolotl researcher Johannes Holtfreter, requires that the water be filtered through a carbon and particulate filter, a UV light, and treatment with a dechlorinator, or water that has been deionized or distilled.
The solution is made as follows:
Holtfreter’s Solution (per liter of water)
NaCl (salt – non-iodinized) 3.46 grams
KCl (potassium chloride) 0.05 grams
CaCl2 (calcium chloride) 0.1 grams
NaHCO3 (sodium bicarbonate) 0.2 grams
Pre-mixed formulas are also available for purchase at your local pet supply store. Regardless of your water concoction, Axolotls need to be kept in a tank with a good filter and gentle water flow. You will need a filter with adjustable flow. Axolotl gills can easily be damaged by high, rapid water flow and poor water quality.
Before your Axolotl aquarium is ready for your pet to live in it, the tank will need time to cycle for ammonia conversion to nitrite, and finally nitrate. During this 4-6 week period, you will need to perform frequent water changes to remove these compounds. Use a test kit and watch for spikes in ammonia and nitrite, until it finally reaches the appropriate level of nitrate. Once you are fully converting to nitrate, you will need to keep your nitrate levels low with regular water changes. Live plants can take up a portion of the nitrate, but it is better to do regular water changes to remove other stressful components of water quality along with the nitrate.
You do not need a heater in an Axolotl tank. In warmer climates, you may even need to add a chiller to your tank to keep your water within the optimum temperature range. The ideal temperature for Axolotls is between 60-64° F (16-18° C). Axolotls do not hibernate, so you do not need to worry about varying the temperature seasonally. Make sure your tank is kept out of direct sunlight, which can cause temperature swings and increased algae growth.
When housing Axolotls, keep in mind that they are very curious and will attempt to ingest anything that looks or smells like food. This includes any substrate (e.g., rocks, gravel) you place in your tank. Anything smaller than 3 cm will be ingested. Bowel obstructions are common in Axolotls and may require surgery to correct.
If you suspect your Axolotl may have been eating something they shouldn’t, contact your local exotic or aquatic veterinarian as soon as possible. DO NOT attempt to correct the obstruction yourself.
Large rocks are best for substrate and will also give your Axolotls spaces to find privacy. You can add some fake or real plants to your tank, but remember to keep them soft in order to prevent skin tears.
The most important thing you can do to support your Axolotl’s health is to provide clean water and good diet. Like all other aquatic tanks, your Axolotl tank will require regular maintenance. When it comes time for maintenance, you will need a siphon to get between rocks and crevices to remove waste. A regular gravel siphon will not work well for this, but you can use the siphon tubing without the siphon. You will also need to perform regular water changes, physically removing old tank water and replacing it with new, appropriately conditioned water. The amount and frequency of changes will depend on your filter and tank capacity, how many Axolotls you keep, and how much they are fed. The most common cause of disease in all aquatic animals is secondary to poor water quality.
Before You Begin — Finding an Aquatic Veterinarian
Before you begin, find your nearest aquatic veterinarian and have their information handy if any issues present themselves. The following sources can help you to find your closest aquatic vet:
Gresens, J. An Introduction to the Mexican Axolotl (Ambystoma mexicanum). Lab Animal. 33:9 (4-47).
Ambystoma Genetic Stock Center (AGSC). University of Kentucky.