The Axolotl

The Axolotl is a species of salamander that is closely related to the tiger salamander. It is also known as the Mexican salamander (Ambystoma mexicanum) or Mexican walking fish, although instead of a fish it is actually an amphibian.

Physical Description: 

Sexually mature males (at about 18-24 months) range in length from 6-18 inches (15-45 cm) with sizes closer to 9 in inches (23 cm) being the most common and any individual over 12 inches (30 cm) is pretty rare. axolotls possess features that are usually typical of salamander larvae, including external gills and a caudal fin extending from behind the head to the vent.

They have wide heads and they have no eyelids. They possess underdeveloped looking limbs that have long, thin digits. Males can be distinguished by their swollen cloacae (that's their boy parts for anyone that doesn't know) lined with papillae while the females are distinguished by their wide bodies that are full of eggs. Three pairs of gill stalks called rami originate behind their heads and help move oxygenated water. The external gill rami are lined with filaments to increase surface area for gas exchange. There are four gill slits lined with what's called gill rakers that are hidden underneath the external gills.



Axolotls have barely visible vestigial teeth which would have developed if they were a normal salamander that had gone through normal salamander metamorphosis. That's the thing about Axolotls, they don't go through the same process that other salamanders do, because instead of going through development and setting foot on land,Axolotls remain in the water once they reach adulthood. Their primary method of feeding is through suction, which is done by their rakers interlocking to close the gill slits. External gills are used for breathing, although buccal pumping (gulping up air from the surface) may also be something they use to gather much needed oxygen.


Axolotls come in very few colors. The two normal colors are "wildtype" (various shades of brown with spots) and melanoid (black). The two mutant colors are leucistic (pale pink with black eyes), and albino (golden, tan, or pale pink with pink eyes).

Fast Tracking to Adulthood

Axolotls exhibit something called neoteny, meaning that they reach adulthood without going through the typical metamorphosis that all other salamanders normally go through. Many species in the same genus are either entirely neotenic, or have neotenic properties. It is something that has been observed in all salamander families and seems to be a survival mechanism that only occurs in aquatic environments in the mountains and hills where this little food and a lack of iodine. Unlike some neotenic salamanders, metamorphosis can be induced in Axolotls through an injection of iodine or by shots of thyroxine hormone. An adult can look like a species of terrestrial plateau tiger salamander, but it has several differences which include longer toes which supports its status as a separate species.

Basically, if there is a generous amount of iodine in their environment, the salamander larvae can ingest it either directly or indirectly through cannibalism, and then they quickly go through metamorphosis and become mature adults with higher dietary requirements, but because Axolotls don't live in these types of environments, they don't which allows them to live and thrive on less.

If you want to find out more about Axolotls and how they were used as a model organisms before anyone learned about their neotony you can look right here.

Habitat

Axolotls are only native to two lakes in Central Mexico: Lake Xochimilco and Lake Chalco. Lake Chaico no longer exists as it was artificially drained to avoid periodic flooding and Lake Xochimilco is a remnant of its former self, only existing as a series of canals. The water temperature in Lake Xochimilco rarely rises above 20 degrees Celsius (which is 68 degrees Fahrenheit), though it may fall even lower in the winter months.

Axolotls are members of the Ambystoma tigrinum (Tiger salamander) 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, but there is a population of tiger salamanders that also inhabit the Axolotls' habitat.

Diet

Axolotls are carnivorous, consuming small creatures such as worms, insects, and small fish in the wild. They locate their food by smell, and will "snap" at any potential meal, sucking the food into their stomachs by vacuum forces.

Conservation Status: 

The Axolotl is listed as critically endangered on the IUCN's red list of endangered species. Current population numbers are unknown, but it is known that the numbers have declined significantly according to surveys that have been done since 2002.

Main Threats: 

 The species is suffering due lake drainage and the growing population of Mexico City. They are also under threat from harvesting for consumption by local people as well as pollution, and degradation of the canal system of Lake Xochimilco. Introduced predatory fish into their environment is also a grave threat to the species. 

What's Being done? 

Conservation action focusing on conserving the species is focused on raising the profile of Lake Xochimilco through conservation education and a nature tourism initiative, along with work on habitat restoration. An action plan for conserving the species is currently underway. This species is protected under the category Pr (Special Protection) by the government of Mexico and is in the process of being amended to a higher category. The Axolotl is currently at Appendix II on CITES, restricting international trade to protect the species from over-harvesting in the wild, where it has been listed since 1975. However the species is currently undergoing the process of "Review of Species included in CITES Appendices."