The Axolotl (Ambystoma mexicanum), also known as the Mexican walking fish, is an aquatic salamander. The axolotl is an unusual amphibian as they are neotenic, which means that it can reach adulthood without undergoing metamorphosis.
For example, like how an aquatic tadpole would become a land-dwelling frog, the axolotl typically doesn't undergo this transformation into a land-dwelling salamander (except in very rare circumstances). The axolotl can live its entire life and reproduce in its larval stage. (There's more about axolotl metamorphosis at the end of this article.)

They are renowned in scientific studies for their ability to regenerate limbs, their spinal cord, gills, heart, and even parts of their eyes and brain. Axolotls are also known for their unusual appearance and their relatively easy care requirements.

Axolotls are fascinating and unique aquatic creatures that make excellent pets for experienced aquatic hobbyists. Here is a comprehensive guide on how to keep an axolotl healthy and happy.

Housing

Axolotls require a spacious and secure aquarium to move around and feel comfortable. A minimum of a 60 litre, 2ft long tank, is recommended for a single axolotl, with an additional 30 litres of space for each additional axolotl.

Adult axolotls can grow just over 30cm (1ft) in length and live for 15 years.

We recommend the aquarium should have a lid or net cover to prevent the axolotl from accidentally jumping out of the aquarium if spooked.

Your axolotl's aquarium should have a filter to keep the water clean. Axolotls are messy eaters, so there is often a high biological loading on the system due to food waste. External hang-on or canister filters are most suitable as they can handle much higher biological loading than internal filters can.

Axolotls are cold water creatures and the temperature should be around 15-20°C. You can use a thermometer to monitor it.
The temperature should stay within this range most of the year, but during summer the temperature may rise. If you notice the temperature rising above 20°C, you can put ice cubes in the aquarium or run a cooling fan or a chiller to keep the tank cool.

Axolotls are relatively inactive creatures, but they still require enrichment to keep them stimulated and healthy. You can add live or fake plants to their aquarium to create a more natural environment. Do not use sharp or pointed decorations that could harm your axolotl. Provide your axolotl with dark hiding spots, such as PVC pipes or ceramic caves, especially if you are running lights to grow plants as they are light-sensitive.

Having a substrate is good as it provides a place for beneficial bacteria to live. The substrate should be fine sand or large river stones. Be careful of using any gravels or substrates that the axolotl may inadvertently ingest. Smaller stones can result in intestinal blockages and even death.

For more information, see our guide on setting up an aquarium.

Lighting

It remains unclear whether axolotls benefit from UVB lighting. While other amphibians and reptiles require UVB to produce vitamin D3 in their skin, which is necessary for calcium absorption and preventing metabolic bone disease, axolotls spend most of their time at the bottom of a lake and are sensitive to bright light. As a result, many keepers do not recommend UVB light for axolotls. If UVB light is provided, a maximum UVI of 1-2 is recommended, such as from a Reptile One UVB 2.0 or ExoTerra UVB 100 globe.

Ensure that there are plenty of plants and hides for the axolotl to take refuge from the light as they are sensitive to bright light. The light should not cover more than a third of the animal's enclosure. Additionally, any lighting for plants should be turned off at night to provide a normal day/night cycle.

Water

Axolotls are aquatic creatures and require clean and fresh water to survive. You should change 25-50% of the water in the aquarium each week or every fortnight, depending on the number of axolotls and the size of the aquarium. Make sure the new water is free of chlorine and other harmful chemicals by using a water conditioner.

Test your water regularly to make sure it is free from ammonia and nitrites.
Axolotls like a pH between 7.4-7.6, however, will tolerate anything between 6.5 to 8.0.

Nitrates are the end product of the nitrogen cycle and should be kept below 40 ppm. If your nitrates are rising too high, dilute them by conducting a water change.

Axolotls also like water that is slightly hard, meaning that there is a good concentration of dissolved salts and minerals. Tap water in most areas is hard, and it should already be hard enough to meet the requirements of your axolotl. It's crucial to keep in mind that mineral salts differ from table salt, and you must not use table salt to regulate hardness levels in your axolotl tank.
Aim for a GH between 7-14 degrees (125-250ppm) and a KH between 3-8 degrees (53-143ppm).

Feeding

Axolotls are carnivorous and require a varied diet of live or frozen-thawed prey. You can feed them various foods, including earthworms, bloodworms, brine shrimp, and pellets. Feed your axolotl once a day, and remove any uneaten food after 10-15 minutes to prevent it from fouling the water.

Axolotls are ambush predators with poor eyesight and they rely on other senses. They can detect movement. Axolotls typically have to be hand-fed non-live foods as sometimes they will not sense something is in their tank if it is not moving.
This can be done using feeding tongs.

Handling

Handling axolotls can be very stressful for them and they should not be taken out of water for this purpose. In case handling is required, vinyl gloves should be worn as the salts and oils present in human skin can be harmful to amphibians. Never pick up an axolotl by its tail, as this can cause injury or damage to their spinal cord.

Health

Keep an eye on your axolotl's health and behavior. If you notice any signs of illness or distress, consult with a veterinarian immediately.

Although generally hardy, axolotls can experience problems such as ammonia poisoning, poor water quality, and impactions from substrate. Additionally, exposure to betadine can cause their gills to regress.

A lack of appetite should be considered concerning for amphibians as they are typically avid eaters. Additionally, the presence of skin lesions or damage to the gills can be indicative of illness.

The most common health issue we see in Axolotls is uncontrolled floating.

Typically, there are a few correctable issues that are associated with this problem. The primary reasons or issues that can result in axolotls floating are:

• Ingesting air while feeding, which leads to floating.
• Impaction can be a cause of floating.
• An ammonia spike may occur (check your water parameters).
• Gas accumulation in the axolotl's gut.
• Floating may be caused by sinking pellets causing bloat as the pellets expand.

However, the most common cause we see is typically underfeeding. Simply, if an axolotl's stomach is empty and full of air, it will float.

Breeding

Males tend to have cloacal bulges and are generally more elongated with longer tails. Females tend to be rounder.

The time at which axolotls reach sexual maturity depends on various factors, such as food quality, water temperature, and the conditions in which they are kept. Males usually mature at a faster rate than females, which generally mature after about 18 cm (7 inches) in total length. Breeding should not be attempted until axolotls are at least 18 months old, and females should not be bred until they reach full size. Breeding female axolotls too early can be detrimental to their health, as they may produce over 1000 eggs, which takes a toll on their metabolism.

Axolotls can be bred at any time of the year, and exposure to natural daylight plays a crucial role in simulating the seasons. Courtship behaviour in axolotls is triggered either by changes in the length of the light period or by a sudden change in temperature.

The breeding setup should have plants for the female axolotl to lay its eggs on and flat, rough pieces of stone for the male to deposit its spermatophores.

Spawning is initiated by the male, who swims around and nudges the female's vent occasionally and then leads her around the tank.

In the world of salamanders and newts, the spermatophore is a common method of sperm transfer. This consists of a bundle of sperm attached to a cone of jelly. The male deposits multiple spermatophores around the tank and tries to guide the female over them. The female picks up the sperm cap from one or more spermatophores using her cloaca, leading to internal fertilization. Sometimes, the female nudges the male's vent, leading to a dance around the tank.

A few hours to two days later, the female begins to lay her eggs one by one. If available, she will lay them on the leaves of plants, but if not, she will attach them to any object in the tank, such as rocks or pipes. The number of eggs laid can vary from 100 to over a thousand depending on the size and condition of the female. Once the female has finished laying, it's best to remove both her and the male from the tank.

In terms of hatching the eggs, a well-aerated tank with an air pump and stone at one end will aid in the hatching process. The eggs typically take around 2 to 3 weeks to hatch, and optimal development occurs when the eggs are attached to plants, which facilitates the exchange of gases. If the eggs are fertile, the majority should hatch. If kept at a temperature of 20 °C, they should hatch after approximately 17 days. Note that if the mother is albino, the eggs will lack pigment and be white, but the pigment will appear during embryo development if the offspring are not albino.

Conclusion

Keeping an axolotl can be a rewarding experience if you provide them with proper housing, water, enrichment, feeding, handling, and healthcare. Remember to do your research and learn as much as you can about axolotls before bringing one home. Axolotls require a significant amount of care and attention, and they are not suitable for everyone. If you are an experienced aquatic hobbyist looking for a unique and easy-to-care-for pet, an axolotl may be the perfect choice for you.

Some interesting things about Axolotl metamorphosis and biology.

Axolotls are fascinating creatures and I find it incredibly difficult to write about them without veering off into a tangent about their unusual evolutionary features.

Axolotls (Ambystoma mexicanum) are in the Tiger Salamander (Ambystomatidae) family, however, their evolution branched off and they don't normally undergo metamorphosis to enter a land-dwelling adult stage. They instead are neotenic and stay in their larval form permanently.  This is a result of a process called paedomorphosis, which can occur in some amphibians and involves the retention of juvenile traits into adulthood

It is believed to have evolved this way because the aquatic stage requires less energy and therefore less food. This means that the Axolotl can exist in niche habitats that a regular salamander cannot.

Salamander metamorphosis typically begins through a thyroid-stimulating hormone, which makes the thyroid produce thyroxine. Axolotls however do not produce this hormone. 
Wild Axolotls come from a very small population and inhabit a small habitat consisting of just a few lakes in Mexico. While not fully understood, it is theorised that this thyroid inactivity is caused by the low iodine levels in this habitat.

Interestingly, even though the Axolotl doesn't produce thyroxine, if you were to give it thyroxine from another salamander species, the Axolotl would undergo metamorphosis and become a land-dwelling salamander. Although it should be noted that this is not a recommended practice and can be harmful to the animal. Thyroxine treatment has been used experimentally to induce metamorphosis in axolotls, but it can also cause developmental abnormalities and shorten lifespan.

Similarly, if there is enough iodine present in the water, their thyroid becomes active and is able to produce thyroxine and the axolotl will metamorphose into a salamander.

Now I strongly don't recommend attempting to metamorphose an Axolotl into a salamander as it's incredibly risky and they don't thrive or live anywhere near as long as an aquatic axolotl. But its a very interesting evolutionary adaptation to a very unique environment.

Axolotls have been studied in science since 1863, and are incredibly important due to their ability to regenerate limbs, their spinal cord, gills, heart, and even parts of their eyes and brain. They are valuable in developmental biology, genetics and biomedical engineering.