Axolotls

Axolotl Anatomy

The Axolotl is unusual in nature because it retains its larval form into adulthood. In fact, it becomes sexually mature in this state. This adaptation, known as neoteny, is often viewed as a backward step in evolution because it prevents the axolotl from living on land, and as a result, it can't colonise new habitats. However, it has led to the axolotl being quite successful in its native habitat, at least until the arrival of man.

The Axolotl is carnivorous and has reasonably typical internal carnivore anatomy, with the main exception of the teeth. Its teeth are pedicalate (i.e. they're small stumps, like cones). With these it grips its food, manoeuvering it into position before swallowing it whole. It has a three-chambered amphibian heart (unlike the mammalian four-chambered heart), and, like all amphibians, it is poikilothermic (its body temperature is dependent upon its surroundings).

Axolotls are famous for their fabulous regeneration ability. Regeneration studies carried out around the world often involve the Axolotl. For example, a young axolotl that loses a foot to a sibling 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. Entire limbs can be regenerated and even portions of the brain and spine.

Larval axolotls tend to be transparent for their first few weeks of life, or until the skin has thickened and pigment cells have proliferated over the body, so the organs are quite visible, as well as the progress of any food in the digestive tract.

One thing to note is that although they retain larval morphology, they do develop rudimentary lungs, and axolotls can be seen to occasionally rise to the surface, take a quick gulp of air to fill these lungs, and then quickly descend to the bottom once more. From my observations, I believe that the lungs develop shortly after the rear legs reach their full length.

Axolotl Habitat

The Mexican Axolotls, like its name implies, is native to parts of Mexico. Found in the high-altitude lakes near Mexico City, the axolotls is historically native to the lakes of Chalco and Xochimilco. Unfortunitly, today only Lake Xochimilco is there and along with the drying up of Lake Chalco, much of the Axolotls' habitat dried up with it. Due to this decrease in native habitat, the Axolotls is listed on the CITES endangered species list and is close to extinct in the wild. Recently, the Axolotl has started making its come back but not in the wild, but in a fish tank near you. The axolotls has been put in the spot light appearing on National Geographic's top ten weirdest animals as number one. This fascinating animal has caught the eye of many amphibian lovers, not only with its distinct external gills but also the variety of color patterns they are found in. To learn more about how to care for your axolotls, visit Caring for your Axolotls.

The axolotls is also housed in many genetic testing centers. It is being used as a model organism in many experiment on hormone levels, genes taken from the Axolotl hearts, pigmentation, vision, and developmental gene expression. Even though the axolotls many be located on the endangered species list, one can still find the embryos at the Ambystoma Genetic Stock Center.

The Axolotl is an aquatic salamander that possess external gills to help in the process of respiration. These external gills are a characteristic that is usually found in the larval form of most salamanders, the Mexican Axolotls is unable to go through metamorphosis to change into an adult form. This characteristic is one of the most unique adaptations that classifies the Axolotl. To learn more about the axolotls adaptations, you will have to continue on to Adaptations.

Extras

Facts

• Axolotls leave the egg with small feathery gills, a tail, and two outgrowths from the sides of their heads that allow them to attach to a substrate. As they grow, their gills increase in size and they develop legs.

• They may release 300–1100 eggs per spawning. The eggs are gelatinous and stick to surfaces in the tank. They need good oxygen levels to develop, and their rate of development depends on the temperature.

• Axolotls (Ambystoma mexicanum) are gilled amphibians. They are unmetamorphosed larvae of the Mexican salamander.

• Axolotls respire (breath oxygen) through their cartilaginous gills, like fish, as well as cutaneously, that is, by diffusing oxygen that has dissolved in the water through their skin. Larger, older axolotls supplement their oxygen supply by filling their rudimentary lungs at the surface of the water.

• Axolotls inhabit an area to the south east of Mexico City. In ancient times, they were eaten by the Aztecs.

• Their natural breeding season is spring. The length of the day and the temperature of the water are thought to influence the start of breeding.

• Axolotls have a cartilaginous skeleton that, even in larger, older axolotls, doesn't become completely calcified. Their muscles are similar to those of fish. They have fine teeth on their upper and lower jaws that they use to grab their food and puncture it. It is thought that this helps their digestive enzymes to penetrate the food.

• Axolotls excrete only half of their nitrogenous wastes as weak urine. The rest is excreted through their gills.

• Sexing axolotls may be difficult unless there is one of each gender to compare. In the male, the cloaca (the external opening of the intestine) is larger and more swollen around the margins. The male's head is also narrower, and its tail is longer than the female's.

• Axolotls are unusual because they are capable of reproduction in their larval state, a phenomenon called neotony. This is usually at twelve months of age.

• Axolotls have no eyelids.

Pictures

Axolotl Feeding Habits

Axolotls are carnivores, implying they require 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. When a hand-fed axolotl becomes accustomed to people, it may occasionally latch onto a finger. You can feel these little teeth quite distinctly. This is a curious experience, rather than a painful one, because the axolotl hasn't the strength to pierce human skin, so don't be afraid to try it. The Axolotl's teeth come into their own when trying to grip something slippery like an earthworm. The worm will wriggle but it will find it very difficult to escape the Axolotl's mouth. If the worm is too large to swallow completely, the Axolotl will eventually give up and let go. Large food is a problem when you don't have biting teeth!

While reading this page, you may find the Health Page worth a look too. It covers some of the dangers of live foods, as well as touching on some nutritional problems. Live "feeder fish" in particular are known to carry disease and are often infected with parasites. These are passed on to whatever eats the fish, and in our case that's our poor axolotl.

The name "Ambystoma" means cup-mouth, and axolotls do have large, wide mouths. When an axolotl wants to eat something, it opens its mouth suddenly and water rushes in, along with the food or anything else around (such as parts of other axolotls, or pieces of gravel). This vacuum action often results in a sudden lurch of the axolotl up into the water and then the animal settles down again.

Axolotls will eat live or dead food. The movement of live food like a worm is a great stimulus for the axolotl to "snap", and indeed, for newly hatched axolotls movement is the only stimulus to which they will respond. Earthworms are a good food source for adult axolotls, but be sure to get them from a source that doesn't use chemicals (such as an organic garden). Better still, raise them yourself if you have the space.

Water-based live foods can be risky because they can be a source of disease. However, if taken from fish-free waters, they tend to be a lot safer (no hosts for the parasites usually means no parasites). Tubifex, although a good food, is not nutritionally balanced for axolotls, and Tubifex can also carry parasites, dangerous bacteria, and other diseases. There are also reports that Tubifex attack salamander eggs. Tubifex are often mistakenly called bloodworms in the US, and shouldn't be confused with the true bloodworms, the larvae of chironomid midges. Freeze-dried and frozen Tubifex are safer than live, although freeze-dried isn't very nutritious.

Axolotl Reproduction

Axolotls can reach sexual maturity anywhere between 5 months and several years, depending on frequency and quality of food, and the water temperature and conditions in which the animals are kept. My personal record for a fully mature male is just under 6 months (at 25 cm or 10 inches).

Axolotls generally begin to mature once they have reached about 18 cm (7 inches) in total length. Females tend to take a little longer to mature than males (usually a difference of a month or two). The Biology Page has a great deal of information about sexing axolotls and their sexual maturity.

It is advisable that you don't attemt to breed axolotls until they reach at least 18 months of age. This gives them time to reach their full size (greater than 30 cm or 12 inches in many cases) and condition (a female ready to breed will be very round towards the end of the body when viewed from above). In my opinion it is safe to breed males at an earlier stage than females, because they have much less physical output during the mating process than females, and therefore there is less strain on their bodies. However, females should be prevented from breeding until they reach their full size.

There is a very good reason for not breeding your female axolotl(s) too early. A female axolotl can lay in excess of 1000 eggs. Producing so many eggs is a strain on the animal's metabolism, and the body prioritises production of eggs over body growth while the animal is in conditions suitable for breeding. Since females may breed several times each year, as soon as the first batch of eggs are laid, the body attempts to produce new eggs to replace those that have been laid. Female axolotls may fall ill at this point unless due care is taken, and for a female that is still growing in length, the strain is increased. For the same reason, females that have recently bred should be kept away from males for at least a month, preferably two or three, in order for them to recover. From personal experience, I know that just because an axolotl breeds, it doesn't mean it is in good overall health.