Axolotl facts for kids

Kids Encyclopedia Facts
Axolotl
Example showing reduced pigmentation
Conservation status
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Amphibia
Order: Caudata
Family: Ambystomatidae
Genus: Ambystoma
Species: A. mexicanum
Binomial name
Ambystoma mexicanum
(Shaw, 1789)

The Axolotl, Ambystoma mexicanum, is the best known of the Mexican mole salamanders: it belongs to the Tiger Salamander complex. The Axolotl shows neoteny: the larvae do not undergo metamorphosis, so the adults stay aquatic, with external gills.

Natural history

The species evolved in the lake underlying Mexico City. Axolotls are used a lot in scientific research because they can regenerate most body parts, are easy to breed, and have large embryos.

Axolotls are closely related to waterdogs, the larval stage of the closely related Tiger salamanders Ambystoma tigrinum and Ambystoma mavortium. These are common in much of North America and also sometimes become neotenic. The mudpuppies, Necturus, are fully-aquatic salamanders which are not closely related to the axolotl but bear a superficial resemblance.

Wild axolotls are now near extinction due to population growth in Mexico City, and the polluted waters of the lake. Non-native fish, such as African tilapia and Asian carp, have also recently been introduced to the waters. These new fish have been eating the axolotls' young, as well as its primary source of food. The axolotl is currently on the IUCN Red List of threatened species.

Description

AxolotlBE
A captive axolotl

A sexually mature adult axolotl, at age 18–24 months, ranges in length from 15–45 cm (6–18 in), although a size close to 23 cm (9 in) is most common and greater than 30 cm (12 in) is rare. Axolotls possess features typical of salamander larvae, including external gills and a caudal fin extending from behind the head to the vent.

Their heads are wide, and their eyes are lidless. Their limbs are underdeveloped and possess long, thin digits. Males are identified by their swollen cloacae lined with papillae, while females are noticeable for their wider bodies full of eggs. Three pairs of external gill stalks (rami) originate behind their heads and are used to move oxygenated water. The external gill rami are lined with filaments (fimbriae) to increase surface area for gas exchange. Four gill slits lined with gill rakers are hidden underneath the external gills.

Axolotls have barely visible vestigial teeth, which would have developed during metamorphosis. The primary method of feeding is by suction, during which their rakers interlock to close the gill slits. External gills are used for respiration, although buccal pumping (gulping air from the surface) may also be used to provide oxygen to their lungs.

Three Colors of Axolotl
Axolotls displaying variations in color

Axolotls have four pigmentation genes; when mutated they create different color variants. The normal wild type animal is brown/tan with gold speckles and an olive undertone. The four mutant colors are leucistic (pale pink with black eyes), albino (golden with gold eyes), axanthic (grey with black eyes) and melanoid (all black with no gold speckling or olive tone). In addition, there is wide individual variability in the size, frequency, and intensity of the gold speckling and at least one variant that develops a black and white piebald appearance on reaching maturity. Because pet breeders frequently cross the variant colors, animals that are double recessive mutants are common in the pet trade, especially white/pink animals with pink eyes that are double homozygous mutants for both the albino and leucistic trait. Axolotls also have some limited ability to alter their color to provide better camouflage by changing the relative size and thickness of their melanophores.

Habitat and ecology

Ambystoma mexicanum 1
Axolotl in captivity

The axolotl is only native to Lake Xochimilco and Lake Chalco in central Mexico. Lake Chalco no longer exists, as it was artificially drained to avoid periodic flooding, and Lake Xochimilco remains a remnant of its former self, existing mainly as canals. The water temperature in Xochimilco rarely rises above 20 °C (68 °F), though it may fall to 6 to 7 °C in the winter, and perhaps lower.

The wild population has been put under heavy pressure by the growth of Mexico City. The axolotl is currently on the International Union for Conservation of Nature's annual Red List of threatened species. Non-native fish, such as African tilapia and Asian carp, have also recently been introduced to the waters. These new fish have been eating the axolotls' young, as well as its primary source of food.

Axolotls are members of the tiger salamander, or Ambystoma tigrinum species complex, along with all other Mexican species of Ambystoma. Their habitat is like that of most neotenic species—a high altitude body of water surrounded by a risky terrestrial environment. These conditions are thought to favor neoteny. However, a terrestrial population of Mexican tiger salamanders occupies and breeds in the axolotl's habitat.

The axolotl is carnivorous, consuming small prey such as worms, insects, and small fish in the wild. Axolotls locate food by smell, and will "snap" at any potential meal, sucking the food into their stomachs with vacuum force.

Captive care

Ambystoma mexicanum at Vancouver Aquarium
These axolotls at Vancouver Aquarium are leucistic, with less pigmentation than normal.
Axolotl with Grit XRay
This animal was x-rayed several times as part of a research project over a period of two years. It was a normal healthy adult (26.3cm 159.5 gm) at the beginning of the project and lived several more years after the project ended.

The axolotl is a popular exotic pet like its relative, the tiger salamander (Ambystoma tigerinum). As for all poikilothermic organisms, lower temperatures result in slower metabolism and a very unhealthily reduced appetite. Temperatures at approximately 16 °C (61 °F) to 18 °C (64 °F) are suggested for captive axolotls to ensure sufficient food intake; stress resulting from more than a day's exposure to lower temperatures may quickly lead to disease and death, and temperatures higher than 24 °C (75 °F) may lead to metabolic rate increase, also causing stress and eventually death. Chlorine, commonly added to tapwater, is harmful to axolotls. A single axolotl typically requires a 40-litre (11-US-gallon) tank with a water depth of at least 15 cm (6 in). Axolotls spend the majority of the time at the bottom of the tank.

Salts, such as Holtfreter's solution, are usually added to the water to prevent infection.

In captivity, axolotls eat a variety of readily available foods, including trout and salmon pellets, frozen or live bloodworms, earthworms, and waxworms. Axolotls can also eat feeder fish, but care should be taken as fish may contain parasites.

Substrates are another important consideration for captive axolotls, as axolotls (like other amphibians and reptiles) tend to ingest bedding material together with food and are commonly prone to gastrointestinal obstruction and foreign body ingestion. Some common substrates used for animal enclosures can be harmful for amphibians and reptiles. If gravel (common in aquarium use) is used, it is recommended that it consist of smooth particles of a size small enough to pass through the digestive tract. One guide to axolotl care for laboratories notes that bowel obstructions are a common cause of death, and recommends that no items with a diameter below 3 cm should be available to the animal.

There is some evidence that axolotls might seek out appropriately-sized gravel for use as gastroliths based on experiments conducted at the University of Manitoba axolotl colony.


Axolotl Facts for Kids. Kiddle Encyclopedia.