Amphibians

Taricha

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The genus Taricha consists of three species and four subspecies of Western Newts (sometimes referred to as Pacific Newts). All newts are part of the family Salamandridae. The three species within this genus are the California Newt, the Rough-Skinned Newt, and the Red Bellied Newt, all of which are found on the west coast of the USA.

Differentiating between species

The Rough-skinned Newt (T. granulosa) and the California Newt (T. torosa) share several characteristics. Both are light brown to black on the upper body and orange to yellow on the underbelly. They have "pebbly" skin that is not slimy and they may grow to a length of 8 inches, which is large for a salamander. However, there are a few characteristics to tell them apart. Rough-skinned Newts have small eyes with dark lower eyelids, while California Newts have large eyes and light lower eyelids. Also, rough-skinned newts' upper teeth form a V shape, while those of the California newt form a Y shape. However, this is difficult to ascertain on a living specimen.

The Red-bellied Newt is brown on the upper body with a red underbelly, has grainy skin, and grows to between 5.5 and 7.5 inches. It can be distinguished from other coastal newts, not only by its red belly, but also by the lack of yellow in its eyes. Breeding males develop smooth skin and a flattened tail.

Behavior

Taricha spp. eat a diet largely consisting of invertebrates such as Blood worms and mosquito larvae. Most predators associate bright colors with poison (called aposematism) and therefore, if attacked, the newt will take up a defensive position, showing off the bright underbelly. If the predator is not deterred by this display the newt will probably be its last meal. Newts of this genus are primarily nocturnal and may be either fully aquatic or semi-aquatic. None are fully terrestrial as they must enter the water to breed. Juvenile newts, which are known as "efts", are primarily terrestrial until they reach sexual maturity.

Toxicity

All species within the genus Taricha possess the biotoxin tetrodotoxin (TTX), one of the most potent toxins known to science. However, the degree of toxicity varies between species and between populations within a species. In general, the Rough-skinned Newt (T. granulosa) is the most toxic species. Rough-Skinned newts from populations in Northern Oregon are more toxic than those from California and Washington. Those on Vancouver Island, in British Columbia, possess little or no TTX. Taricha can be lethal to humans if ingested and at least one human fatality occurred in Oregon from eating a Rough-skinned Newt. Eastern newts of the genus Notophthalmus (=Diemictylus of earlier authors) also secrete TTX, but in lesser amounts. When handling Taricha the toxins should not be allowed to come in contact with unbroken skin or mucous membranes. Proper hand washing after handling should prevent any problems with infection from Salmonella (which newts are known to carry) or ingestion of TTX, however, some individuals are known to be allergic to skin contact with the toxin. Also, as amphibians' skin is very permeable, hand washing before handling will reduce the possibility of the newt absorbing bacteria or other contaminants from the handler.

These newts are, however, often kept as pets and with proper lighting, feeding and hygiene they will readily adapt to aquarium life.

Oriental Fire-bellied Toad

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The Oriental Fire-bellied Toad, is a small (4 cm, 2") semi-aquatic toad species found in Korea, north-eastern China and adjacent parts of Russia. An introduced population exists near Beijing. They are commonly kept as pets in land and water vivariums.

Description

Oriental fire-bellied toads are the most easily recognizable species of Bombina. They are typically a bright green with black mottling dorsally, but their coat may also darken to brown and even black depending on the scenery presented. Like other Bombina species, Bombina orientalis have a bright yellow to red (generally bright reddish-orange) ventral region mottled with dark brown to black. The skin on their dorsal side is covered in small tubercles. Although it is typically referred to as a toad, the Fire-Bellied Toad is not a member of the toad family (Bufonidae.) As such, it may properly be referred to as a toad.

They are noted for their bright green and black coloration on their backs, and brilliant orange and black on their underside. In the wild, B. orientalis eat various types of small aquatic arthropods (among other things) from which they obtain Carotene, which helps to color their bellies. These bright colors serve as a warning to predators of toxicity. The toxin is secreted through the skin mostly on the hind legs and sometimes the belly in a milky-like substance when the frog is disturbed or frightened. Not only will they emit this toxin, they will also lay on their back to show the colour of the belly, indicating its toxicity to any predators.

Habitat

Like other Bombina species, B. orientalis is mostly aquatic, inhabiting warm, humid forested regions. They spend most of their time in the water, among dense vegetation.The orientalis is also known as the tuti toad.

Reproduction

Breeding takes place in the spring with the warming of the weather and increase in rain. Males call to the females with a light barking croak. They jump onto the back of any other fire-bellied toad that happens to pass by, often leading to male-male confusion, but rarely any sort of fighting. Females lay anywhere from 40 to 100 eggs in a large cluster, usually around submerged plants, near the water's edge. Tadpoles hatch from the eggs in 3–10 days depending on the temperature of the water. The larvae begin to develop legs in 6–8 weeks, and are fully metamorphosed and begin venturing on land in 12–14 weeks.

In captivity

In the United States, B. orientalis is commonly kept as a pet. They are generally a hardy species that do well in captivity if given good water quality. They are commonly fed with small crickets dusted with a calcium powder. They can also be fed with other small insects and grubs. They should not be fed mealworms, as these larva possess hard shells which fire-bellied toads have a hard time digesting or passing.

Fire-bellied Toads are usually fed live food. They only hunt prey which moves, ignoring any food item which is too slow or still. At times, they may even release prey that doesn't put up a strong enough fight. Some keepers have success by "hand" feeding food items, attaching pieces to a long piece of wood or straw and waving it in front of the frogs. Oriental fire-bellied toads can be trained to accept food in this manner.While not the most toxic of amphibians, regular handling is not recommended (avoid if there are cuts on your hands) and your hands should always be washed thoroughly immediately after touching the frog or cleaning the tank. Although harmless to the skin of most, if ingested it can cause discomfort. Because of their mild toxicity, oriental fire-bellied toads should not be kept with most other types of frog or amphibian.

When kept in captivity, it is important to provide adequate hiding places as Bombina orientalis need to feel a sense of security. They tend to spend the majority of their time basking in neck-level dechlorinated water (if they do not completely immerse themselves.) An ideal filter is a type of mini filter, as long as the outlet is blocked in some way ideally by a barrier of stones, it disperses the water better without creating a strong current.

Because members of the Bombina genus have short, round tongues that cannot be pushed out of the mouth, fire-bellied toads cannot spit out items that have been accidentally taken into the mouth. As a result, their enclosures must not include gravel of a size which may be accidentally ingested. Larger rocks, Eco Earth or sand, may be used instead. An animal which swallows a piece of gravel it cannot pass will become impacted and will die unless it receives medical attention.

In captivity, oriental fire-bellied toads have lived for more than a dozen years, with 15 years being common. Some older reports document them as living up to 30 years.

In captivity, providing a source of Beta-Carotene (such as carrots) to the prey insects (crickets) early in a frog's adult stage allows it to develop brighter coloration.

Oriental fire-bellied toads should be kept in water, with some kind of land or island which allows them to periodically climb out of the water. Be careful though, these frogs aren't strong swimmers and may drown in water that is too deep. An ideal enclosure has plenty of land and water-based hiding places, as well as a land-based location suitable for depositing live food. Fire-bellied Toads have a sensitivity to chlorine and chloramine - tap water should be treated or allowed to stand for several days, to allow chlorine to dissipate, before adding it to their environment. Chloramine will not dissipate in this manner, so tap water treated with chloramine must be treated with a dechloramine agent (and then allowed to stand) before being added.

Morelet's Treefrog

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The Morelet's Treefrog is a species of frog in the Hylidae family. It is found in Belize, El Salvador, Guatemala, Honduras, and Mexico. Its natural habitats are subtropical or tropical moist lowland forests, subtropical or tropical moist montanes, freshwater marshes, and intermittent freshwater marches. It is threatened by habitat loss.

Description

The Morelet's Tree Frog (Agalychnis moreletii) is a fairly uncommon frog which has a green body, black eyes and a red or pink underbelly. They belong to the order Anura, which encompases all frogs, the family Hylidae which encompasses specifically tree frogs, the genus agalychnis, or tree frogs native to Central and South America and species moreletii. They have also been called black-eyed leaf frogs and popeye hyla. They are found in moist subtropical lowland mountainous forests and wetland habitats of Belize, Brazil, El Salvador, Guatemala, Honduras and Mexico. They have been collected on the Atlantic and Pacific slopes of Veracruz, Chiapas, the Maya mountains of Belize, northwestern Honduras and El Salvador. They can live in pristine or disturbed habitats and will breed in temporary or permanent bodies of water. They have an extended breeding season during the summer months. They deposit clutches of 50 to 75 eggs on vegetation or rocks over water. The eggs of the Morelet's Tree Frog have a green pigment and when they hatch, the larvae fall into the water to complete their development into frogs.

Threats

The Morelet's Tree Frog was abundant within its range and were kept as pets internationally. However it is currently listed as critically endangered on the IUCN Red List as of 2001 because of habitat destruction and disease. Industry and agriculture are thought to be the main causes of lowland montane forest destruction. The population of Morelet's Tree Frogs are also being decimated due to a disease called Chytridiomycosis, which is an infectious disease that kills amphibians. Chytridiomycosis and habitat destruction are projected to cause the population to decline over 80% in the next 10 years. In some regions, the frogs have gone extinct completely. For example, a study done in 2004, has claimed that Morelet's Tree Frog may be extirpated from the region of Southern Mexico. Small snakes also are predators of the Morelet's Tree Frog.

Conservation Measures

Morelet's Tree Frogs are dying at a rapid rate. Their survival is dependent upon several factors due to their human and disease caused population decline. Some conservation measures are in place, while others are still in need of implementation or research. A number of protected parks have been created to curb habitat destruction in areas of Central America and Mexico. Taxonomic research is currently in place to further understand the population's status. More data is needed, however, on a temporal and spatial scale to determine trends in the population of Morelet's Tree Frogs.

Cranwell's horned frog

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Cranwell's horned frog, also called the Chacoan horned frog, is a terrestrial frog endemic to the dry Gran Chaco region of Argentina. Like most members of the genus Ceratophrys, they are often considered Pacman frogs because of their uncanny resemblance to the popular video game character of the same name. Most adult species range from 8-13 cm long (3-5 in) and can weigh up to 0.5 kg (1 lb).

The backs of these frogs typically have dark green and brown coloration, although albino variants with orange and yellow backs also exist. The dark color scheme aids in camouflaging the animal as it burrows and waits for its prey. Though generally inactive, they are aggressive eaters, and are capable of leaping for several body lengths in order to capture prey.

Cranwell's are nocturnal and rest with their eyelids open. They are ordinarily carnivorous, feeding mostly on insects and like-sized animals, and are known to cannibalize other frogs.

At extreme temperatures, Cranwell's frogs enter a period of estivation, developing a thick layer of protective skin to trap moisture and aid in respiration. When estivation is complete, the frog uses its front and hind legs to help shed the protective layer. In many cases, the frog uses its jaws to help pull the skin over its back, often eating the skin in the process.

Like many Pacman frogs, Cranwell's are very popular as pets. As such, they should be kept in a humid environment such as an aquarium with moist substrate (not gravel). They should be fed a mixed diet of gut-loaded crickets, mealworms, small mice, and feeder fish. As a rule of thumb, these frogs should be fed every 1–2 days until the age of 18 months, at which point they should be fed once every 4–7 days.

Because of their large mouths, these frogs are particularly susceptible to impaction, a condition whereby the frog's gastrointestinal tract is obstructed by a foreign body accidentally swallowed. The foreign body can be almost anything, but in Pacman frogs kept as pets, it is commonly a small rock or piece of gravel used as substrate. Impaction often leads to constipation and malnutrition, and possibly death unless treated promptly with laxatives such as the osmotic diuretic lactulose. In severe cases, the volume of feces in the intestines is so large that the lungs are obstructed and the frog's breathing is impaired. Surgery is often the only alternative in these cases, although it is rarely performed because of its typically prohibitive costs.

California Newt

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The California newt is a newt. It is also referred to as the orange bellied newt. They can grow to be 8 inches (20 cm) in length.

Range and habitat

California newts exist primarily on the California coastline and in the Sierra Nevada. This is because they prefer less humid climates than the rough skinned newts. During the non-breeding season the newts are land dwelling, preferring rock crevices and logs. While breeding, the subspecies torosa torosa prefers slow moving pools in coastal streams.

Reproduction

Reproduction occurs generally between December and early May. Typically the adult newts will return to the pool in which they hatched. After a mating dance, the male mounts the female and rubs his chin on her nose. He then attaches a spermatophore to the substrate, which she will retrieve into her cloaca.

The egg mass released by the female contains between 7 and 30 eggs, and is roughly the consistency of a thick gelatin dessert. Typically the egg masses are attached to stream plant roots or to rocky crevices in small, slow moving pools. But they have also been known to be attached to underwater rocks or leaf debris. While shallow in a wide sense, these pools are rather deep relative to the average depth of a Southern California stream, varying in depth from about 1 to 2 meters.

Adult newts will stay in the pools throughout the breeding season, and can be occasionally found well into the summer. Larvae hatch sometime in early to mid summer, depending on local water temperature. Larvae are difficult to find in streams as they blend in well with the sandy bottom, which they usually stay close to.

Toxicity and predation

Like other Taricha members, the glands in the skin of T. torosa secrete the potent neurotoxin tetrodotoxin, which is hundreds of times more toxic than cyanide. This is the same toxin found in pufferfish and harlequin frogs. Researchers believe that bacteria synthesize tetrodotoxin and the animals that employ the neurotoxin acquire it through consumption of these bacteria. This neurotoxin is so strong that it is enough to kill most vertebrates, including humans. However, they are dangerous only if ingested, and can be safely kept as pets.

Due to their toxicity, the California newt has few natural predators. Garter snakes are the most common, and some species have developed a genetic resistance to tetrodotoxin.

Diet

Earthworms, snails, slugs, sowbugs, bloodworms, mosquito larvae and other invertebrates are among the California newt's prey. In the Sierras, the newt will also consume trout eggs. In an aquarium habitat, the newt may eat goldfish flake food.

Conservation status

The California newt is currently a California Special Concern species (DFG-CSC). Some populations have been greatly reduced in southern California coastal streams due to the introduction of non-native, invasive species and human habitation. The mosquitofish (Gambusia affinis) and red swamp crayfish (Procambarus clarkii) have caused the greatest reduction in newt populations.

Introduced as fish bait and stock pond prey, red swamp crayfish are an incredibly aggressive, prolific, and stalwart species that will prey upon newt larvae and egg masses. The crayfish will also disrupt newt breeding via competition for space during the summer mating season and physically antagonizing adults. Crayfish will typically maul the adult newts with their claws, and subsequent infection can lead to death. T. torosa are present in streams with introduced crayfish often sport tails with several notches removed. They are amphibians and live in humid areas.

Bullfrog

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The American Bullfrog is an aquatic frog, a member of the family Ranidae, or "true frogs", native to much of North America. This is a frog of larger, permanent water bodies, swamps, ponds, lakes, where it is usually found along the water's edge. On rainy nights, bullfrogs along with many other amphibians, go overland and may be seen in numbers on country roads. American bullfrogs live longer in warm weather. They have been widely introduced across North America (see range map). The original, naturally determined range did not include far western regions where it is found today.

Description

Bullfrogs grow on average to be about 3 and a half to 6 inches (9-15 cm) long in bodylength (although there are records of some as big as 8 inches), legs add another 7-10 inches (17 - 25 cm) to length. Adult bullfrog skeleton is representative of tetrapod vertebrates, comprising an axial skeleton (skull and vertebrae) and an appendicular skeleton (pectoral girdle and forelimbs, pelvic girdle and hindlimbs). Ranids, however, lack ribs. The pronounced pair of dorsal humps in the back of ranid frogs are the ends of the pelvic ilia, homologues of the human hips.

The bullfrog skull is highly fenestrated. The orbits open ventrally through the roof of the mouth to accommodate eye retraction during locomotion and swallowing. The skull bears a continuous row of tiny teeth on the maxilla and premaxilla and a pair of small vomerine teeth on the palate. The mandible is toothless.

The bullfrog nervous system consists of a brain, spinal cord, and peripheral nerves including cranial nerves, spinal nerves, and sympathetic nerves serving organs such as the heart, gastrointestinal tract, kidneys, gonads.

Females have an eardrum (tympanum) the same size as their eye. Males' eardrums are larger.

Ecology and behavior

Respiration

Ranid frogs absorb oxygen and eliminate carbon dioxide through their moist skin, the lining of the mouth, and the lungs. When in the air, as opposed to underwater, frogs continuously elevate and lower the floor of the mouth, which serves to ventilate the mouth, or buccal cavity, and exchange gases through the richly vascularized lining of the mouth. Periodically, the regular rhythmic pumping of the floor of the mouth is interrupted by a deeper lowering of the throat at the extreme of which the glottis opens and the throat muscles contract vigorously to force air from the mouth into the lungs—the nostrils are closed off. This lung ventilation may be performed several times after which the shallow buccal ventilation resumes. Lacking ribs, frogs must supply the pressure to force air into their lungs, whereas mammals can enlarge the cavity surrounded by the rigid rib cage and allow the atmosphere to supply the pressure.

Reproduction

Fertilization is external in ranid frogs. In the mating grasp, or amplexus, the male rides on top of the female, grasping her with his forelimbs posterior to her forelimbs. The female bullfrog deposits her eggs in the water and the male simultaneously releases sperm.

Breeding begins in late spring or early summer. Males defend and call from territories, attracting females into a territory to mate. The call is reminiscent of the roar of a bull, hence the frog's common name. A female may produce up to 20,000 eggs in one clutch.

Growth and development

Eggs hatch in 3–5 days. Time to metamorphosis ranges from a few months in the southern to 3 years in the northern parts of the geographic range. Maximum lifespan in the wild is estimated at 8–10 years, but one captive lived almost 16 years.

Feeding

Stomach content studies going back to 1913 suggest the bullfrog preys on any animal it can overpower and stuff down its throat. Bullfrog stomachs have been found to contain rodents, small turtles, snakes, frogs including bullfrogs, birds, even a bat, as well as the many invertebrates which are the usual food of ranid frogs. These studies furthermore reveal the bullfrog's diet to be unique among North American Rana in the inclusion of large percentages of aquatic animals, e.g., fish, tadpoles, Planorbid snails, Dytiscid beetles. The specialized ability of bullfrogs to capture submerged and large strong prey comprises a pronounced biting motor pattern that follows up on the initial and typical ranid tongue strike. Adaptation to target image displacement due to light refraction at the water-air interface consists of the bullfrog's application of tongue surface comparatively posterior to the perceived location of the prey target. The comparative ability of bullfrogs to capture submerged prey, compared to that of the green frog, leopard frog, and wood frog (R. clamitans, R. pipiens, R. sylvatica, respectively) was also demonstrated in laboratory experiments.

Prey motion elicits feeding behavior. First, if necessary, the frog performs a single orienting bodily rotation ending with the frog aimed towards the prey. This is followed by approaching leaps, if necessary. Once within striking distance, the bullfrog emits its feeding strike, which consists of a ballistic (eyes closed as during all leaps) lunge that ends with the mouth opening, extension of the fleshy and mucous-coated tongue upon the prey, often engulfing it, while the jaws continue their forward travel to close (bite) in close proximity to the prey's original location just as the tongue is retracted back into the mouth, prey attached. Large prey that do not travel entirely into the mouth are literally stuffed in with the forearms. In laboratory observations, bullfrogs taking mice usually dove underwater with prey in mouth, apparently with the advantageous result of altering the mouse's defense from counterattack to struggling for air. The tiny teeth of bullfrogs are useful only in grasping. Asphyxiation is the most likely cause of death of endothermic (warm-blooded) bullfrog prey.

Human use

While occasionally kept as pets, the American Bullfrog provides a minor food source, especially in the Southern United States and in some areas of the Midwestern United States. In a few locations they are commercially cultured in ponds, but the traditional way of hunting them is to paddle or pole silently by canoe or flatboat in streams or swamps at night; when the frog call is heard, a light is shone on the frog to temporarily inhibit it. The frog will not jump into deeper water as long as movement is slow and steady. When close enough, the frog is gigged and brought into the boat. In some states, breaking the skin while catching them is illegal and either grasping gigs or hand capture are used. The only parts eaten are the rear legs, which resemble small chicken drumsticks and, sometimes, the backs, which are usually fried for consumption.

The American Bullfrog is also used as a specimen for dissection in many schools across the world.

The American Bullfrog is the state amphibian of Iowa, Missouri, and Oklahoma.

The American Bullfrog have been introduced to many countries in the world, such as South Korea, and have become a nuisance to the country's natural ecology for its appetite that can devour a small snake.

Axolotl

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The axolotl , Ambystoma mexicanum, is the best known of the Mexican neotenic mole salamanders belonging to the Tiger Salamander complex. Larvae of this species fail to undergo metamorphosis, so the adults remain aquatic and gilled. The species originates from the lake underlying Mexico City and is also called ajolote (which is also the common name for the Mexican Mole Lizard). Axolotls are used extensively in scientific research due to their ability to regenerate most body parts, ease of breeding, and large embryos. They are commonly kept as pets in the United States, Great Britain, Australia, Japan (sold under the name wooper looper and other countries.

Axolotls should not be confused with waterdogs, the larval stage of the closely related Tiger Salamanders (Ambystoma tigrinum and Ambystoma mavortium), which are widespread in much of North America and also occasionally become neotenic, nor with mudpuppies (Necturus spp.), fully-aquatic salamanders which are not closely related to the axolotl but bear a superficial resemblance.

As of 2008, wild axolotls are near extinction due to urbanization in Mexico City and polluted waters. Nonnative 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 International Union for Conservation of Nature's annual Red List of threatened species.

Description

A sexually mature adult axolotl, at age 18–24 months, ranges in length from 15–45 centimetres (5.9–18 in), although a size close to 23 centimetres (9.1 in) is most common and greater than 30 centimetres (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 in order to provide oxygen to their lungs. Axolotls have four different colours, two naturally occurring colours and two mutants. The two naturally occurring colours are wildtype (varying shades of brown usually with spots) and melanoid (black). The two mutant colours are leucistic (pale pink with black eyes) and albino (golden, tan or pale pink with pink eyes).

Habitat and ecology

The axolotl is only native to Lake Xochimilco and Lake Chalco in central Mexico. Unfortunately for the axolotl, Lake Chalco no longer exists as it was drained by humans to avoid periodic flooding, and Lake Xochimilco remains a diminished glimpse 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 or 7 °C (45 °F) in the winter, and perhaps lower. The wild population has been put under heavy pressure by the growth of Mexico City. Axolotls are also sold as food in Mexican markets and were a staple in the Aztec diet. They are currently listed by CITES as an endangered species and by IUCN as critically endangered in the wild, with a decreasing population.

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. 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.

Axolotl's neoteny

Axolotls exhibit a property called neoteny, meaning that they reach sexual maturity without undergoing metamorphosis. Many species within the axolotl's genus are either entirely neotenic or have neotenic populations. In the axolotl, metamorphic failure is caused by a lack of thyroid stimulating hormone, which is used to induce the thyroid to produce thyroxine in transforming salamanders. The genes responsible for neoteny in laboratory animals may have been identified; however, they are not linked in wild populations, suggesting artificial selection is the cause of complete neoteny in laboratory and pet axolotls.

Unlike some other neotenic salamanders (Sirens and Necturus), axolotls can be induced to metamorphose by an injection of iodine (used in the production of thyroid hormones) or by shots of thyroxine hormone. Another method for inducing transformation, though one that is very rarely successful, involves removing an axolotl in good condition to a shallow tank in a vivarium and slowly reducing the water level so that the axolotl has difficulty submerging. It will then, over a period of weeks, slowly metamorphose into an adult salamander. During transformation, the air in the vivarium must remain moist, and the maturing axolotl sprayed with a fine mist of pure water. The odds of the animal being able to metamorphose via this method are extremely small, and most attempts at inducing metamorphosis lead to death. This is likely due to the strong genetic basis for neoteny in laboratory and pet axolotls, which means that few captive animals have the ability to metamorphose on their own. Artificial metamorphosis also dramatically shortens the axolotl's lifespan if it survives the process. A neotenic axolotl will live an average of 10–15 years (though an individual in Paris is credited with achieving 25 years), while a metamorphosed specimen will scarcely live past the age of five. The adult form resembles a terrestrial Mexican Tiger Salamander, but has several differences, such as longer toes, which support its status as a separate species.

Use as a model organism

Six adult axolotls (including a leucistic specimen) were shipped from Mexico City to the Jardin des Plantes in Paris in 1863. Unaware of their neoteny, Auguste Duméril was surprised when, instead of the axolotl, he found in the vivarium a new species, similar to the salamander. This discovery was the starting point of research about neoteny. It is not certain that Mexican Tiger Salamanders were not included in the original shipment.

Vilem Laufberger of Germany used thyroid hormone injections to induce an axolotl to grow into a terrestrial adult salamander. The experiment was repeated by the Englishman Julian Huxley, who was unaware the experiment had already been done, using ground thyroid hormones. Since then, experiments have been done often with injections of iodine or various thyroid hormones used to induce metamorphosis.

Today, the axolotl is still used in research as a model organism, and large numbers are bred in captivity. Axolotls are especially easy to breed compared to other salamanders in their family, which are almost never captive bred due to the demands of terrestrial life. One attractive feature for research is the large and easily manipulated embryo, which allows viewing of the full development of a vertebrate. Axolotls are used in heart defect studies due to the presence of a mutant gene that causes heart failure in embryos. Since the embryos survive almost to hatching with no heart function, the defect is very observable. The presence of several color morphs has also been extensively studied.

The feature of the salamander that attracts most attention is its healing ability: the axolotl does not heal by scarring and is capable of the regeneration of entire lost appendages in a period of months, and, in certain cases, more vital structures. Some have indeed been found restoring the less vital parts of their brains. They can also readily accept transplants from other individuals, including eyes and parts of the brain—restoring these alien organs to full functionality. In some cases, axolotls have been known to repair a damaged limb as well as regenerating an additional one, ending up with an extra appendage that makes them attractive to pet owners as a novelty. In metamorphosed individuals, however, the ability to regenerate is greatly diminished. The axolotl is therefore used as a model for the development of limbs in vertebrates.

Captivity

Axolotls live at temperatures of 14 °C (57 °F)-20 °C (68 °F), preferably 17 °C (63 °F)-18 °C (64 °F). As for all cold-blooded organisms, lower temperatures result in slower metabolism; higher temperatures can lead to stress and increased appetite. Chlorine, commonly added to tapwater, is harmful to axolotls. A single typical axolotl typically requires a 40 litres (8.8 imp gal; 11 US gal) tank with a water depth of at least 15 centimetres (5.9 in). Axolotls spend a majority of the time at the bottom of the tank.

In laboratory colonies, adult axolotls are often housed three to a one-gallon container, and water changes are performed more regularly. 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.