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Axolotl

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What is Axolotl?

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The Mexican walking fish, or axolotl, is a neotenic salamander similar to the tiger salamander. While it is often referred to as a "walking fish," the axolotl is an amphibian, not a fish. The species was first discovered in several lakes, including Lake Xochimilco, which lies beneath Mexico City. Axolotls are unique to amphibians in that they do not go through metamorphosis to reach adulthood. Adults remain aquatic and gilled rather than taking to the ground.


Axolotls are not to be confused with waterdogs, the larval stage of the closely related tiger salamanders (A. tigrinum and A. mavortium), which are found throughout most of North America and may become neotenic at times. Mudpuppies (Necturus spp.) are fully aquatic salamanders that are not closely related to axolotls but have a superficial resemblance.


Due to urbanisation in Mexico City and the resulting water contamination, as well as the introduction of invasive species such as tilapia and perch, wild axolotls were on the verge of extinction as of 2010. The International Union for Conservation of Nature and Natural Resources (IUCN) lists them as critically endangered in the wild, with a declining population, and as an endangered species under the IUCN's CITES treaty. Because of their capacity to regenerate limbs, axolotls are often used in scientific research. Axolotls were a staple of the Aztec diet and were sold as food in Mexican markets.

Scientific Classification of Axolotl Larva

Kingdom: Animalia 

Phylum: Chordata 

Class: Amphibia 

Order: Urodela 

Axolotl Family: Ambystomatidae

Genus: Ambystoma 

Species: A. mexicanum 

Physical Characteristics 

At the age of 18–24 months, a sexually mature adult axolotl animal can be anywhere between 15 and 45 cm (6–18 in) long, with a height of about 23 cm (9 in) being the most common and greater than 30 cm (12 in) being uncommon. External gills and a caudal fin that extends from behind the head to the vent distinguish axolotls from salamander larvae. When salamanders reach maturity, they typically lose their external gills, though the Axolotl retains them. This is due to Axolotls' neoteny evolution, which has resulted in them becoming much more aquatic than other salamander species. Refer to the below axolotl larva diagram for a better view and understanding.

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Their eyes are lidless and their heads are big. Their bodies are underdeveloped and their digits are long and small. Males are distinguished by their swollen cloacae, which are lined with papillae, while females are distinguished by their broader bodies, which are filled with eggs. External gill stalks (rami) protrude from behind their heads and are used to transport oxygenated water. To increase surface area for gas exchange, the external gill rami are lined with filaments (fimbriae). Underneath the external gills, four-gill slits lined with gill rakers prevent food from entering while allowing particles to flow through.


Vestigial teeth form during metamorphosis in axolotls and are scarcely visible. Suction feeding is their main mode of feeding, during which their rakers interlock to close the gill slits. External gills are used for respiration, but buccal pumping (sucking air from the surface) can also be used to provide oxygen to their lungs. Buccal pumping can be done in two ways: two-stroke, which pumps air from the mouth to the lungs, and four-stroke, which reverses the direction with compression forces.


Axolotls have four pigmentation genes, each of which produces a different colour variant when mutated. Brown/tan with gold speckles and an olive undertone is the typical wild type animal. Leucistic (pale pink with black eyes), golden albino (golden with gold eyes), axanthic (grey with black eyes), albino (pale pink/white with red eyes), melanoid (all black/dark blue with no gold speckling or olive tone), and axanthic (grey with black eyes) are the five most common mutant colours. Furthermore, the scale, frequency, and severity of the gold speckling vary greatly between individuals, and at least one version matures with a black and white piebald appearance. Animals that are double recessive mutants, particularly white/pink animals with pink eyes that are double homozygous mutants for both the albino and leucistic trait, are popular in the pet trade since pet breeders often cross the variant colours. Axolotls may also change their colour to provide better camouflage by adjusting the size and thickness of their melanophores.

General Characteristics of Axolotl

  • Previously, the larval stage of the Axolotl was referred to as Siredon. It was later discovered to be Ambystoma larva.

  • It has three pairs of external crimson gills and four pairs of open gill clefts. The eyes, nostrils, and mouth are all found on the head.

  • The larva lives for a long time. The body, which measures about 27 cm in length, is divided into three sections: head, trunk, and tail. A caudal fin is attached to the tail. Both the forelimbs and the hindlimbs are present.

  • It reaches sexual maturity and begins to lay eggs.

  • In captivity, axolotl larvae grow into adults. Thyroid injections may be used to cause a metamorphosis in Axolotl larvae. Metamorphosis can be easily induced in six-month-old axolotls. As the larva grows older, metamorphosis to adulthood becomes more complicated. It is possible to cause partially metamorphosed terrestrial animals to return to the larval stage.

Reproduction and Development

  • Axolotls are unique in that they can reproduce while still in their larval stage, a phenomenon known as neoteny. This generally happens at about the age of twelve months.

  • If you don't have one of each gender to compare, sexing axolotls can be difficult. The cloaca (the intestine's external opening) is thicker and swollen around the edges in males. The man also has a narrower head and a longer tail than the female.

  • Spring is their normal breeding season. The start of breeding is thought to be influenced by the duration of the day and the temperature of the water.

  • Fertilisation is internal.

  • Each spawning can result in the release of 300–1100 eggs. The eggs are gelatinous and adhere to the tank's surfaces. To develop, they require adequate oxygen levels, and their rate of development is influenced by temperature.

  • Axolotls have small feathery gills, a tail, and two outgrowths from the sides of their heads that enable them to stick to a substrate when they hatch. Their gills get bigger and they get legs as they get older.

  • Small axolotls, especially those under 10 centimetres in length, often eat one another, but survivors can live for ten to twelve years.

Habitat and Ecology 

The axolotl is only found in the Valley of Mexico's freshwater lakes of Xochimilco and Chalco. Lake Chalco has been drained as a flood control measure, and Lake Xochimilco is a relic of its former self, consisting mostly of canals. The water temperature in Xochimilco seldom exceeds 20 degrees Celsius (68 degrees Fahrenheit), though it can drop to six to seven degrees Celsius in the winter, and possibly lower.


In its Lake Xochimilco ecosystem, surveys in 1998, 2003, and 2008 found 6,000, 1,000, and 100 axolotls per square kilometre, respectively. However, a four-month search in 2013 found no living individuals in the wild. Two wild ones were discovered a month later in a network of canals leading from Xochimilco.


The urbanisation of Mexico City has put a strain on the wild population. The axolotl is currently on the annual Red List of endangered species published by the International Union for Conservation of Nature. Non-native fish including African tilapia and Asian carp have also been introduced to the waters recently. The axolotls' young, as well as their primary source of food, have been eaten by these new fish.


Axolotls, like all other Ambystoma species in Mexico, are members of the tiger salamander, or Ambystoma tigrinum, species complex. Like most neotenic animals, they live in a high-altitude body of water surrounded by a dangerous terrestrial climate. These circumstances are thought to encourage neoteny. In the axolotl's habitat, however, a terrestrial population of Mexican tiger salamanders lives and breeds.


In the wild, the axolotl eats small prey such as worms, insects, and small fish, and it is a carnivore. Axolotls use their sense of smell to detect food and will "snap" at any possible meal, drawing it into their stomachs with vacuum energy.

Uses of Axolotl 

The axolotl is still used as a model organism in science today, and significant numbers are bred in captivity. In comparison to other salamanders in their genus, which are almost never captive-bred due to the demands of terrestrial life, they are particularly easy to breed. The large and easily manipulable embryo, which allows viewing of a vertebrate's full growth, is one appealing feature for study. Owing to the existence of a mutated gene that causes heart failure in embryos, axolotls are used in heart defect research. The deficiency is easily visible since the embryos survive almost to hatching without having a heart. Because of the similarities between human and axolotl neural plate and tube development, the axolotl is an excellent animal model for studying neural tube closure. Unlike frogs, the axolotl's neural tube is not covered under a layer of superficial epithelium. Other organ systems are also affected by mutations, some of which are poorly understood and others which are. The genetics of axolotl colour varieties has also been extensively researched.

Regeneration 

The healing ability of the axolotl is the attribute that attracts the most attention: the axolotl does not heal through scarring and is capable of regenerating entire damaged appendages in a matter of months, as well as more important structures like the tail, limb, central nervous system, and tissues of the eye and heart in some cases. They can also resurrect sections of their brains that aren't as essential. They can also accept transplants from other people, such as eyes and brain parts, restoring full functionality to these alien organs. Axolotls have been known to patch a damaged limb while also regenerating a new one, resulting in an extra appendage that makes them appealing to pet owners as a novelty. Individuals that have metamorphosed, on the other hand, have a significantly reduced ability to regenerate. As a result, the axolotl is used as a model for vertebrate limb growth.


Axolotls are thought to have a different mechanism during limb generation to control their internal macrophage level and suppress inflammation, as scarring prevents proper healing and regeneration. Other studies, however, have cast doubt on this view.

Genome

The axolotl genome sequence, which is 32 billion base pairs long, was published in 2018 and is the world's largest animal genome to date. It discovered species-specific genetic pathways that could be involved in limb regeneration. Despite being about ten times the size of the human genome, the axolotl genome encodes a similar number of proteins, 23,251. (the human genome encodes about 20,000 proteins). The disparity in size is largely explained by a high proportion of repetitive sequences, but these repeated elements also lead to increased median intron sizes (22,759 bp), which are 13, 16, and 25 times larger than those found in human (1,750 bp), mouse (1,469 bp), and Tibetan frog (906 bp), respectively.

Captive Care

Like its relative, the tiger salamander, the axolotl is a common exotic pet (Ambystoma tigerinum). Lower temperatures cause a slower metabolism and a significantly decreased appetite in all poikilothermic species. Temperatures of about 16 °C (61 °F) to 18 °C (64 °F) are recommended for captive axolotls to ensure adequate food intake; stress caused by more than a day's exposure to lower temperatures can quickly lead to disease and death, and temperatures of more than 24 °C (75 °F) can cause metabolic rate increases, which can cause stress and eventually death. Axolotls are poisoned by chlorine, which is usually applied to drinking water. A 40-gallon (150-litre) tank is normally needed for a single axolotl. The bulk of the time, axolotls spend at the bottom of the tank.

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To avoid contamination, salts such as Holtfreter's solution are normally applied to the water.

Axolotls in captivity consume a range of foods such as trout and salmon pellets, frozen or live bloodworms, earthworms, and waxworms. Feeder fish may be eaten by axolotls, but caution should be exercised because the fish can contain parasites.

Axolotls (like other amphibians and reptiles) eat bedding material with their food and are vulnerable to gastrointestinal obstruction and foreign body ingestion, so substrates are a critical factor for captive axolotls. Amphibians and reptiles may be harmed by certain common substrates used in animal enclosures. If gravel is used (which is popular in aquariums), it should be made up of smooth particles that are small enough to move through the digestive tract. Bowel obstructions are a common cause of death in axolotls, according to one guide to axolotl treatment for laboratories, and no objects with a diameter less than 3 cm should be accessible to the animal.


Based on experiments conducted at the University of Manitoba axolotl colony, there is some evidence that axolotls can seek out appropriate-sized gravel for use as gastroliths.

Some Popular Axolotl Larva Comments and Cultures 

  • The axolotl is one of a number of nonsense terms adopted by Mad Magazine for use as running gags, most of which are of international origin; potrzebie and veeblefetzer are two others.

  • The Tleilaxu use a technology called "axlotl tanks" to regrow limbs in Frank Herbert's fictional Dune universe.

  • In his 1956 collection Final del Juego, Argentine writer Julio Cortázar included a short storey titled "Axolotl." The plot revolves around a man who becomes fascinated with salamanders after seeing them in a Paris aquarium.

  • Yolanda Buenaventura, an anthropomorphic axolotl character voiced by Natalie Morales, appears in the Netflix series BoJack Horseman.

  • The axolotl, along with illustrations of maize and chinampas, will be featured on the latest logo for Mexico's 50-peso banknote, which will be unveiled in 2020. By 2022, the banknotes are expected to be in circulation.

  • Axolotls will be introduced to the sandbox game Minecraft in an upcoming update, according to Mojang Studios at Minecraft Live 2020.

Interesting Facts About Axolotls

  • Axolotls live in a region to the east of Mexico City. They were eaten by the Aztecs in ancient times.

  • Axolotls (Ambystoma mexicanum) are amphibians with gilled skin. They are Mexican salamander larvae that have not yet metamorphosed.

  • Axolotls have a cartilaginous skeleton that does not become fully calcified, particularly in bigger, older axolotls. The muscles in their bodies are identical to those of fish. Their upper and lower jaws have fine teeth that they use to grasp and puncture their food. This is thought to aid the penetration of their digestive enzymes into the food.

  • Like fish, axolotls breathe oxygen through their cartilaginous gills as well as cutaneously, that is, by diffusing oxygen dissolved in the water through their skin. The oxygen supply of larger, older axolotls is supplemented by filling their rudimentary lungs at the water's surface.

  • About half of an axolotl's nitrogenous waste is excreted as poor urine. The remainder is excreted by their gills.

  • Axolotls have no eyelids.

Conclusion 

Axolotls are probably one of the most scientifically studied salamanders in the world. In this article, we can go through characteristics, habitat and ecology, uses, genome, regeneration, captive care and some of the popular axolotl cultures. The recent development of essential genetic and genomic tools for the axolotl brings us closer to identifying mechanisms of paedomorphic development and understanding the role of thyroid hormone in the development and evolution of axolotl.

FAQ (Frequently Asked Questions)

Q1. Where is the Axolotl Larva Found?

Answer. They're mostly found in the Xochimilco lake complex near Mexico City, and they're different from most other salamanders in that they don't live in water all of the time.

Q2. Why are Axolotls illegal in California?

Answer. Axolotls are banned in California not because they are endangered, but because they are considered "detrimental species" and pose a threat to native wildlife. Axolotls cannot be imported from other nations into other states, such as New Mexico.

Q3. How Often Should Axolotls be Fed?

Answer. The amount to feed depends on the axolotl's size, maturity level, and water temperature. Since axolotls take two to three days to digest their food, they only need to be fed two to three times a week.

Q4. How Do Axolotls Die?

Answer. One of the most common causes of axolotl death is poor water quality, which may occur without the owner's knowledge. It occurs as a result of carelessness. Although a filter is needed, some owners prefer to keep their axolotls in tanks without one.