The Axolotl is unusual in nature because it retains its larval form into adulthood.pdf

7/27/2019 The Axolotl is unusual in nature because it retains its larval form into adulthood.pdf

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The Axolotl is unusual in nature because it retains its larval form intoadulthood. 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'resmall stumps, like cones). With these it grips its food, manoeuvering it into positionbefore 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).

One thing to note is that although they retain larval morphology, they dodevelop 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.

Axolotls are famous for their fabulous regeneration ability. Regenerationstudies 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 bere

ge

ne

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an

dev

enpo

rti

ons

ofth

ebr

ai

nan

dsp

in

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The diagram on the right is a summary of the development of the Axolotl, from egg

to adult. The red line below each animal represents roughly 2 mm. The egg (stage

1) is typically amphibian. It comprises of the embryo, which measures about 2 mm

in diameter, and also the surrounding layers of jelly. The jelly is the product ofwater and a substance that is secreted around the egg when it is laid. Stage 2 is theembryo prior to hatching. At this stage it is approximately 11mm in length. Stage 3

is the young larva, prior to the growth of limbs.


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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.

After approximately two weeks, the larva reaches stage 4. Like all other

caudates (newts and salamanders), and unlike anurans (frogs and toads), the front

legs develop first, followed within a few weeks by the hind legs.At stage 5 the axolotl is, to all intents and purposes, a miniature adult. I once

saw a friend's female axolotl that was about 43 cm (17 inches) in length. However, a

large size for most axolotls would be 25-30 cm (10-12 inches). The average seems tobe about 23-25 cm (9-10 inches). Adults tend to reach their full size after eighteen

months to two years, the growth rate depending on how well they are fed and at

what temperature they are kept. I've raised axolotls to 26 cm in 7 months, butthat's exceptionally fast.

Thetwo pictures

on the leftand right

are of ayoung adult

female

(hence thelack of eggs

which wouldnormally

give the

female amuch more

rounded

appearance)

. Noticethat one ofher gill

branches is

held in a

differentorientation

to normal

(the gill on

the left

actually).

I have

redrawn the

diagram in

Peter Scott's book (see Books and Links)of the Axolotl's digestive system on a realaxolotl, in order to better illustrate the

proportions and help us to visualise the

internal arrangement of the organs.

Imagine you're seeing through the animal.The cloaca/vent is on the underside.

Sexual Maturity

Male and female axolotls differ in a

number of ways. Peter Scott gives a fewpointers, but some of these seem to be


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rather inaccurate and unreliable. There are only two reliable methods of

distinguishing males from females.

The first is that mature females tend to have very rounded bodies, due to the

number of eggs present in their bodies. And the most reliable is that the sexually

mature male's cloacal region is swollen, while that of the sexually mature female is

considerably less so. See the photos at the bottom of this page.Males generally reach sexual maturity slightly earlier than females, and mature

males tend to be more elongated, and longer tails than females.

One point of note is that white, golden, and albino axolotls that have reachedsexual maturity will have dark brown tips to their toes. The soles of their feet may

even appear "dirty" (see the photo below). In wild type and melanoid animals thetoe tips become slightly paler than the rest of the body, at maturity, but it is

harder to see than in the lighter colour variants.

Male axolotls go through a cycle where, although sexually mature, they maynot have sperm available for mating. In the wild this seems to be determined tosome extent by the seasons. However, in captivity it's less regular and may occur at

any time of the year. It usually takes the male about 2-3 months to produce spermand perhaps a further 2 months for the sperm to move into the vas deferens so thatit is available for mating. This could mean that the overlap between having and not

having sperm available could be a few weeks to a few months.

Dark toe tips on lightly coloured axolotls indicate sexual maturity.

The first photo below is of the cloacal region of a mature male and the secondis of a mature female's cloacal region. The male is a golden albino, while the femaleis a melanoid albino. Their cloacas are circled in blue.

Male GoldenAlbino


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Femalemelanoid albino

Welcome! This web site is devoted to the Axolotl (pronounced Ax-oh-lot-ul),scientific nameAmbystoma mexicanum. The site describes the Axolotl's

background, biology, and care in captivity. You will also find information aboutthe Tiger Salamander,Ambystoma tigrinum andAmbystoma mavortium spp.,

because these animals are closely

related.

Australians and New Zealanders

frequently refer to the Axolotl as theMexican Walking Fish, though the Axolotl

is not a fish but an amphibian, asalamander, part of the order

Caudata/Urodela. Because it's asalamander, it's part of one of the three

branches of class Amphibia, which also

includes the frogs andtoads (the Anurans), and the mainly eel-like order, Gymnophiona, which are also

known as the Caecilians. Have a look at

the Biology Page for a short guide to the Axolotl's body and characteristics. One

common misconception is that axolotls and other salamanders are lizards orreptiles. In fact, amphibians are a completely separate group of animals. Forexample, did you know that reptiles and human beings have a four-chambered

heart? Well amphibians have only three chambers. That's just one example of how

appearance can be deceiving: salamanders might look like lizards, but they are very

different indeed.

This page is a brief introduction for those new to the Axolotl and salamanders.

If you require specific information, you can search this site using the search facility

at the top right of this page. Caudata.org also contains a wealth of axolotl

information and it's a great place to buy axolotls or trade with other hobbyists.Caudata.org is the Internet's premier source of salamander and newt informationand it places an emphasis on their maintenance in captivity. There is a very busy

axolotl forum at Caudata.org, used by people just like you. I hope that you find thissite useful, but most of all I hope you enjoy what you read and find here. If you're

looking for

information aboutmetamorphosed

axolotls, click here.

Axolotls ofvarious colours occurin captivity,

including grey,

shades of brown,leucistic (white with

black eyes), goldenalbino, white albino,


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as well as other varieties, such as the melanoid (a near-black animal). The normally

coloured axolotl, the "wild type", can be near-black like the one in the group photo

to the left, chocolate brown like the one in the site's logo, or even creamy incolour, and anywhere in between. There are even "piebald" axolotls in various

colours, and a variety that is piebald in more than one colour, known as the"harlequin". You can learn more about how colour comes about and how it is passed

on by taking a look at the Genetics Page. And why not take a look at the hundredsof photos of the weird and wonderful varieties of axolotls submitted by enthusiastslike yourself at the Axolotl Section of the Caudata.org User Photo Galleries?

The name "Axolotl" comes from the Aztec language, "Nahuatl". One of the most

popular translations of the name connects the Axolotl to the god of deformations

and death, Xolotl, while the most commonly accepted translation is "water-dog"(from "atl" for water, and "xolotl", which can also mean dog).

Prior to the growth ofMexico city in the basin of

Mexico, the Axolotl was

native to both Lake

Xochimilco, and Lake Chalco.Of these two high altitude

freshwater lakes, only the

remnants of Xochimilco as

canals can be seen today.Unfortunately manyinformation sources mention

these lakes as if they still

exist (such as this ill-researched article about ametamorphosed axolotl on

the BBC News Web site). If

only this were still the case:sadly it is rarely caught in thewild but at least the Axolotl isnow on the CITES endangered

species list. There have been

efforts to breed and releasethe animal, in order to re-

establish its numbers.However the location of the

remaining waterways where

the animal may live (locatedin the Mexico City

metropolitan area) are likelyto be very threatened by the city's continuing expansion and the days of the species

surviving in the wild are surely quite limited. Fortunately, due to the importance ofthe Axolotl in scientific research, it is unheard of for them to be taken from the

wild for that purpose because of the huge numbers bred in captivity each year.

There are related MexicanAmbystoma species that also remain gilled as adults.These species are located in water bodies further from Mexico city and may have a

slightly brighter future in the wild than the Axolotl.

Despite its endangered status, the use of the Axolotl as a laboratory animal

should ensure the species' survival, if only in captivity. It has long been known thatthe Axolotl is a worthy study due to its amazing healing and regeneration abilities.

Normal wound healing in animals occurs through the growth of scar tissue, which is

not the same as the original tissue, nor is it as robust. Normal wound healing alsodoes not allow for most animals to re-grow a lost limb. However the axolotl is fully


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capable of complete limb re-growth. The animal has the added scientific attraction

of having especially large embryos, making it easier to deal with under laboratory

conditions. Its embryo is also very robust, and can be spliced and combined withdifferent parts of other axolotl

embryos with a high degree ofsuccess.

The Axolotl is a fascinatingcreature for a number of

reasons, including its grotesqueappearance, its ability to

regenerate, and primarily the

fact that it exhibits thephenomenon known as

neoteny. Ordinarily,amphibians undergo

metamorphosis from egg to

larva (the tadpole of a frog is alarva), and finally to adultform. The Axolotl, along with a

number of other amphibians,

remains in its larval form throughout its life. This means that it retains its gills and

fins, and it doesn't develop the protruding eyes, eyelids and characteristics of otheradult salamanders. It grows much larger than a normal larval salamander, and itreaches sexual maturity in this larval stage. Another term to describe this state is

"perennibranchiate". The animal is completely aquatic, and although it does possess

rudimentary lungs, it breathes primarily through its gills and to a lesser extent, itsskin.

It is

generally

acceptedthatneoteny isa

"backward

" step inevolution,

becausethe

Axolotl is

descendedfrom what

were onceterrestrial

salamanders, like

the

closelyrelated

species, the Tiger Salamander,Ambystoma tigrinum andAmbystomamavortium spp. (in fact, one likely theory suggests that the Axolotl is in fact a Tiger

salamander off-shoot, as it can interbreed with that species with some success).

Through some quirk of nature, a neotenous form developed and, probably due toenvironmental conditions, prospered. Neoteny is sometimes found in otheramphibians, but tends to be caused by low levels of iodine (an essential element for

animals to make thyroxine hormones, necessary for growth and development), or

possibly by random genetic mutation. Research has also shown that very low


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temperatures can suppress the production of these hormones, thus also inducing

neoteny.

In the Axolotl, neoteny is now totally genetic (click for more information on

the Axolotl's genetics). When treated with hormones, the axolotl will usually begin

to metamorphose, but in very rare cases it will metamorphose spontaneously, such

as the metamorphosed wild type axolotl pictured here. The metamorphosed wildtype axolotl bears a close resemblance to the Mexican race of the TigerSalamander,Ambystoma velasci. There is a wonderful thread on the Caudata.org

forum here about the metamorphosed axolotl in the photo.

Breeding AxolotlsBefore reading this page, you may find it helpful to first read the Biology

Page and the Genetics Page.

BasicsAxolotls can reach sexual maturity

anywhere between 5 months and severalyears, depending on frequency and

quality of food, and the water

temperature and conditions in which theanimals are kept. My personal record for

a fully mature male is just under 6months (at 25 cm or 10 inches).

Axolotls generally begin to matureonce 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 cmor 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 lessphysical output during the mating process than females, and therefore there is less

strain on their bodies. However, females should be prevented from breeding untilthey reach their full size.

There is a very good reason for not breeding your female axolotl(s) too early. Afemale 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 maybreed 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 axolotlsmay 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 twoor three, in order for them to recover. From personal experience, I know that justbecause an axolotl breeds, it doesn't mean it is in good overall health.

Breeding methodsMost sources state that the breeding season for axolotls is from December to

June. However, they can be bred at any time of the year, although most success is


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reported in the early part of the year. The former Indiana University Axolotl Colony

used changes in the length of light period to trigger spawning. Males and females

are subjected to a decreasing "daylight" period over a few weeks, and then theduration of lighting is steadily increased. They then put a male and a female

together and courtship behaviour usually follows.

An alternate school (Peter W. Scott and some others) instead recommends asudden change in temperature to trigger courtship behaviour. Keeping the pairseparately for a few weeks at 20-22 C (68-71 F) and then transferring them both

into a tank with a water temperature at least 5 C lower frequently triggerscourtship behaviour. In fact, Scott recommends 12-14 C (54-57 F). My own

experience, and that of some others, is that this thermal shock method usually just

stimulates the male. In order for this procedure to be successful, the female mostbe receptive and ready to breed.

In my experience, by keeping axolotls in a room that receives at least partialseasonal change in temperature and light period (if there is a window in the room),

breeding will occur naturally, usually at least once before the peak of winter and

once in the spring, if the animals are adequately fed.

As mentioned briefly above, exposure to natural day length throughout theyear by having the tank in a room that receives natural light is a good idea because

light seems to have at least as an important role as temperature in simulating the

seasons.

A pair of axolotls kept in good conditions should breed at least once a year,

albeit unpredictably. Axolotls may spawn for no obvious reason, at "odd" times ofthe year, as mine have done in the past. Axolotls may surprise you.

My Breeding Setup

The breeding setup that Iuse routinely is furnished withmany plants (plastic plants are

good because they don't rot,

but I also use clumps of live

Java Moss, Vesiculariadubyana). The plants are forthe female axolotl to affix her

eggs (pictured on the right is a

female melanoid albino in the

process of laying its eggs onplastic plant leaves). Slates orflat, rough pieces of stone

should be placed on the

bottom of the tank for themale to deposit its

spermatophores.Spermatophores are packets of

sperm - you can read more on

these in the courtship andspawning section.

Spermatophores will not readily stick to bare glass or plastic, so in order for matingto be successful the spermatophore must be stationary during courtship. It is usually

a good idea to put the tank in a room where it will be left alone, so as not todisturb the pair.


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Courtship and SpawningSpawning is initiated by

the male, who swims around,

raising its tail and making

vigorous writhing motions. The

male nudges the female's ventoccasionally and then leads her

around the tank. The

spermatophore is a common"device" in the salamander andnewt world (an old one, about

12 hours old, is pictured beside

this paragraph). It is a packet

of sperm attached to the top ofa cone of jelly. The male

deposits between 5 and 25 of these around the tank and attempts to lead the

female over them. She picks up the sperm cap (from one or more spermatophores)

in her cloaca - fertilisation takes place internally. She may also nudge the male'svent, and this can lead to a prolonged "dance" around the tank.

Between a few hours and two days later, she commences spawning, laying eachegg individually. She will lay them on the leaves of plants, if available, but if not,

she will place them about the tank, attaching them to rocks, pipes and any other

object available. There may be between 100 and over a thousand eggs laid in onespawning, depending on the size of the female and if she is in optimal condition at

spawning. After the female has finished laying, it's best to remove her and themale.

Hatching EggsPictu

red to theright are

four 12-hour old

eggs. Note

the lackof

pigment -this

indicatesthat the

mother

wasalbino.

Normaleggs are

dark

brown(there is apicture of two at the top of this page). An albino mother will lay white, pigmentless

eggs. If the offspring are not albino, pigment will appear during embryo

development. The eggs take about 2 to 3 weeks to hatch. Development seems to be

optimal when the eggs are attached to plants. This is due to the circulation ofwater around the egg, aiding gaseous exchange.

Assuming the eggs are fertile, the majority of the eggs should hatch if kept inwell-aerated water. An air pump and air stone at one end of the tank will be


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helpful, just be sure it doesn't cause vigorous water flow. At 20 C (68 F) the eggs

should hatch after about 17 days. Have a look at the Embryo Series Photo Log for a

daily photographic account of the development of some white eggs.

Requirements & Water Conditions

OverviewWater quality is an important factor in the health of the Axolotl. They are

forgiving animals, but the correct care of axolotls in captivity is only possible under

the right water conditions. Coupled with water conditions, we must also exercise

caution when considering what to put in the water, be it ornaments or other tankmates.

Topics covered on this page:

1. Other Tank Inmates, & Other Axolotls2. Temperature & Cooling3. Water Flow4. pH: Acidity & Basicity/Alkalinity5. Chlorine & Chloramines6. Ammonia, Nitrite, & Nitrate7. Water Hardness & Dissolved Salts8. Water Changes & Final Words

Other Tank Inmates, & Other AxolotlsHere are the best three words of advice regarding other tank inmates: Just say

no.

Why? Well, let us suppose we would like to keep something with our axolotls,

for instance, a fish, or another salamander or newt. The fish will invariably attemptto nibble on an axolotl's gills. After all, they're so attractive and feathery! The

salamander or newt may try the same trick, particularly at feeding time. Let ussuppose that our axolotl is bigger than the fish or salamander. It's quite likely we'll

end up with one well fed axolotl! There is a simple rule that axolotls follow: if itmoves and it's smaller than our axolotl, it'll end up in our axolotl's stomach. So,follow my three words of advice: Just say no!

Young axolotls, less than 8 cm in length (3 inches), shouldn't be kept togetherin a confined space. If they are to be kept together, it would be wise to use an

aquarium that allows them plenty of space. Young axolotls will nip each other's feet

and gills, more so when very young. Even axolotls up to 15 or 16 cm (6 inches) maynip their tank mates, occasionally inflicting serious damage. This is particularlynoticeable in wild type axolotls, since they are naturally more aggressive

than homozygous colour mutants, and wild types will bite colour mutants in

preference to other wild types. This behaviour is frequently observed by scientists

and hobbyists alike and has yet to be fully explained.


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Cannibalistic tendencies are much reduced in adult axolotls. However adults

will predate upon considerably smaller axolotls, so keep different generations apart

until they all reach adulthood.

Lastly, consider keeping the sexes apart, unless you are prepared to deal with

the occasional batch of eggs.

Temperature & CoolingIf you've been reading the pages in sequence, you will have read on

the Housing Page that the optimum temperature for axolotls is between about

16 C and 18 C (60-64 F). Lower temperatures lead to sluggish behaviour, slowermetabolism, and decreased appetite. Axolotls do not hibernate, so it is not helpful

to cool them below 10 C, although they shouldn't suffer unduly if kept at these

lower temperatures.

Some hobbyists in temperate regions maintain axolotls in outdoor ponds. Theseponds may even ice over during the winter. Provided the winter isn't particularly

harsh or long, axolotls can do quite well under outdoor conditions. Obviously, a food

source must be present during the rest of the year.

Temperatures above 24 C (75 F) are very stressful to axolotls. Such

temperatures cause metabolism to increase (the rate at which the body "works"),and consequently, an increase in appetite. However, the stress resulting from more

than a day or two of exposure to these temperatures will quickly lead to disease

and death. You can read more about axolotl diseases and their treatment onthe Health Page.

The first symptoms of heat stress in axolotls include refusal of food and/or the

development of pale patches of mucus-like material on the skin (see the photo

below).

This axolotl is exhibiting symptoms of heat stress: notethe pale patch of mucus-like material on the head

If you are having difficulty maintaining the temperature of your axolotl'saquarium below 24 C (75 F), there are a few options to consider. The easiest

short-term solution is to move the aquarium to a cooler part of the home.Remember, in every room, the temperature at ground level will be at least 1-2 C(3-5 F) cooler than high up on a shelf. In the summer, the same rule holds true for


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a house as a whole: the lower rooms in the house (or the basement) will be cooler

than rooms on higher floors. So, moving the aquarium may easily allow you to

reduce the temperature in your axolotl tank from 26 C to 23 C. Such atemperature change could make the difference between your axolotl living and

dying.

Remember: if you plan to move an aquarium, make sure you remove most ofthe water first (just leave enough to cover the axolotl). Make sure there is acushioned support at the destination (such as a polystyrene board), and ask

someone to help you carry the aquarium.

In more extreme cases, and in localities where high temperatures persist for

more than a day or two at a time, you will need to take different measures. Some

people use aquarium chillers (proprietary or home-made). I have no experience ofchillers, but the people on the Axolotl Forum should be able to offer you

appropriate advice.

Another commonly used option, which should be safe to use for a week or two

at a time is the "ice bottle". This is aplastic bottle of water, such as the 2 litrebottle (4 pints) used for carbonated soft drinks. The bottle is filled to between 80

and 90% capacity, and then frozen solid. Using a plastic bottle is important - awater-filled glass bottle will explode in the freezer. The bottle is then floated in

the aquarium and the temperature monitored, and if necessary, the bottles are

operated in relays. Larger aquariums would do better with larger bottles (2 L is amaximum though), smaller aquariums would do better with 500 mL bottles (about a

pint).

Using ice bottles safely is a skill: if the temperature changes too much, too

rapidly, it can be more stressful to the axolotls than maintaining a stable, if high,temperature. Typically, ice bottles cause the temperature to crash into the teens

Celsius (50s to early 60s F). After thawing, the temperature will begin to climbback into the mid-to-late 20s once again. Then, if we put another ice bottle back in

to the aquarium, the process repeats itself. This is a fast and effective method tokill an axolotl. This is because the temperature changes so rapidly and does sorepeatedly, stressing the axolotls to the extreme.

So, if you intend to use ice bottles, do so carefully. Do not use them on very

small tanks (under 60 cm/24 inches in the longest dimension). For a larger tank,

using several smaller bottles in succession is probably safer than one large one and

then another large one. And be prepared to switch bottles before the first onethaws out completely so that you can attempt to maintain a relatively constanttemperature.

To summarise tank cooling, the three things you need to worry about are:

1. How rapid is the temperature change? It shouldn't take place in less than30-60 mins.

2. By how much does the temperature change? The larger the change, themore stress it will cause.

3. How stable is the new temperature? Fluctuations are quite stressful.4. How often does the temperature change in 24 hours? If it's more than

twice, you really should consider another option.

There are no absolutes here. We just have to minimise the stress caused bythese factors as best we can. I have a very clear opinion on temperature problems: I

feel that if one can't maintain stress-free conditions for 360 of the 365 days of the

year, one shouldn't keep axolotls.

If your axolotl develops the pale mucus-like patches that the axolotl in thephoto has developed, treat it as you would a fungal infection, but remember that


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treating this condition is not going to be successful if you do not do something about

the temperature too.

Water FlowWater flow is usually caused by a filter or when you use an air pump on an

aquarium. Output from a filter can cause significant flow and this is perhaps themost common cause of stress in axolotls. Excessive water flow will, sooner or later,

lead to disease. The photos below depict an axolotl that has succumbed to thestress caused by excessive water flow.

This golden albino's forward-turned gills are typical of an axolotl stressed by flowing water.

A curled tail end is a sure sign of a stressed axolotl.

Here are several approaches to minimise concentrated water flow, such as thattypical of a filter's outflow:


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1. If the filter has a built-in facility to reduce the flow, use it.2. Use a spray bar. Either make one from a piece of tubing that has had

holes drilled in it, or buy a proprietary spray bar kit, the longer the

better. Orientate it against the glass so that water force is lessened. An

aquarium equipped with such a system is depicted and described on

the Housing Page.3. Angle the filter so that the water flow is aimed at a glass side of the

tank.

4. Angle the filter so that the water flow is directed upwards towards thewater's surface.

5. Partially obstruct the filter's output using a piece of filter wool, or ahome-made device, such as a piece of filter tube. Be careful not to

obstruct the output nozzle too much, as this may cause your filter's

motor and impellor to wear rapidly.

6. Consider using a smaller or different filter.pH: Acidity & Basicity/Alkalinity

pH stands for "power of hydronium". Water (H2O) exists in a constant

equilibrium with itself: H2O OH-+ H

+. The hydrogen ion (H

+) is very small and

strongly hydrated (meaning it attaches itself to another water molecule),

essentially existing as the ion hydronium (H30+). pH is a convenient way of

expressing the hydrogen ion concentration. In actual fact, it's the negative

logarithm of the hydrogen ion concentration. The pH scale ranges from 0 to 14. A

solution (i.e. water containing something else) with a pH of less than 7, is said to be

acidic. A pH greater than 7 is considered basic (also known as alkaline). And a pH ofexactly 7 is considered neutral, neither acidic nor basic. The further the pH is from7, the stronger the acidity or alkalinity/basicity of the solution. You can obtain

simple-to-use pH test kits from your local aquarium retailer.

Most municipalities treat their water so that it is within a few degrees of pH 7(neutral). My local water is 7.2 after treatment. For axolotls, a pH of 6.5 to around8.0 is acceptable, but 7.4 to 7.6 is probably ideal. pH can affect the toxicity of

ammonia and this is discussed below.

If you have particularly acidic or basic water, you can adjust the pH using the

kits sold by your local aquarium retailer, or you can basicify the water by addingsalts, as described in the Water Hardness & Dissolved Salts topic, below.

Chlorine & ChloraminesChlorine is a nasty green gas, denser than air, that was used in the trenches in

World War I. It was dangerous enough to kill people by reacting vigorously with lungtissue. This alarming property is used to kill bacteria in municipal water supplies

around the world today, which makes the water safe for human consumption.

Ammonia (some more info below) is another noxious gas, and manymunicipalities also add it to their water. Chloramines (NH2Cl, NHCl2, and NCl3)

result from a combination of chlorine and ammonia. Unfortunately, aquatic animals

are not top of the list of concerns of Municipalities.

These substances make it necessary to use de-chlorinator in the water before itcan be used in the aquarium. Alternatively, water can be left to stand for 24 hoursor more to let the chlorine dissipate, but be aware that it takes a lot longer for

chloramines to reach safe levels in water if just left to stand. De-chlorinators also

remove chloramines. Most de-chlorinators also remove traces of metals such as iron,mercury, copper, lead, cadmium, and manganese. Metals may be found in waterdue to the pipes through which it must travel.


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I use Aquarium Pharmaceuticals' Stress Coat, which also contains aloe vera, a

plant extract that, although slightly toxic, replaces the natural slime coat that fish

have. It seems to have a similar benefit for axolotls and it's not harmful. Hagen'sAmquel also contains aloe vera. Aloe vera also has a slight anti-biotic effect.

Every time you change the water using tap water, be sure to treat it first for

chlorine and chloramines. If for some reason you're unsure of the presence ofchlorine in the water, you can obtain a chlorine test kit from your local aquariumshop.

Ammonia, Nitrite, & NitrateThese three substances, as discussed on the Housing Page, are part of the

biological filtration cycle in your aquarium. Ammonia, NH3, the main waste product

produced by your axolotls, is very toxic in its unionised form (NH 3 as opposed toNH4

+). A low pH means a higher concentration of H

+ions, which in turn results in a

higher degree of ionisation of NH3 to NH4+. Conversely, a high pH means that

unionised ammonia, toxic NH3, is the main form of ammonia. What this means in

English is that the higher the pH, the more toxic the ammonia. Ammonia can kill,

and at a pH of 8 or more, it kills even more effectively. Water temperature can alsoaffect its toxicity, a higher temperature resulting in a higher toxicity. Unless you're

extremely proficient with maintaining aquarium systems, a periodic ammonia test isadvisable. Even the most experienced hobbyist should occasionally test for

ammonia.

Nitrite, NO2-, is produced from ammonia by the bacterium Nitrosomonas. It is

not as toxic as ammonia, but should also be tested for regularly. Again, test kits areavailable and should be used about as regularly as ammonia tests.

Nitrate, NO3-, is the least toxic of this family of nitrogenous compounds. It is

produced from nitrite by the bacterium Nitrobacter. Although it should be tested

for, regular water changes and plants in the aquarium will keep the levels of nitrate

in check. Although not toxic at low levels, if let build up through lack of waterchanges, it too can be dangerous, and high levels usually lead to blooms of algae.

Water Hardness & Dissolved SaltsThe degree of water hardness can be thought of as the amount of dissolved

salts in the water. There are many kinds of salt apart from the one people use ontheir food. Some commonly encountered salts include epsom salt (MgSO4),

baking/bread soda (NaHCO3), and "Low-Sodium" salt (KCl) used by people as an

alternative to ordinary salt (NaCl).

If you live in a hard water area, the chances are that you've seen limescale inyour kettle or pipes. This is caused by the deposition of dissolved salts of calcium

and magnesium on the heating element of the kettle and the inside surface of the

pipes. Soft water contains little dissolved salts, while hard water containssignificant amounts. There tends to be a correlation between soft water and

acidic pH, and hard water and alkaline pH. This is because these minerals affect thechemical equilibrium in the water (discussed in a simple form in the pH section).

Axolotls prefer somewhat hard water, and those that live in soft water willoften suffer from temporary anaemia - the animal becomes pale and its gills lose

their colouration for a few minutes or hours. This is not a dangerous condition but itcan be prevented by supplementing the hardness of the water with added salts.

Currently, I live in an area in which the water is a little on the soft side. I

regularly supplement it with added salts. Laboratories use one of two types of saltmixture (each is known as a medium) in their water: Holtfreter's solution and

Steinberg's solution. The ingredients and proportions used in each are detailed in


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the table below, together with the "recipe" I personally use. This table includes a

brief version of a table found in "Developmental Biology of the Axolotl".

Medium Components to make 100% concentration

(per litre of water)

Weight ingrams

Holtrefeter's

Solution

NaCl

KCl

CaCl2NaHCO3

3.46

0.05

0.10.2

Steinberg'sSolution

NaClKCl

Ca(NO3)2.4H2OMgSO4.7H2O

Tris (a sort of buffer)

Add HCl to pH 7.4

3.40.05

0.080.2050.56

John's Solution NaCl

MgSO4.7H2O

NaHCO3

1

0.10.1

Indiana University Axolotl Colony use a modified Holtfreter's solution whichleaves out the NaHCO3 and uses MgSO4in the same weight. Typically, 40% or 50% is

used for adults, and 20% for embryos.

I have also used another modified Holtfreter's mix at 50% concentration. Themodification is that I added MgSO4 in the same weight as NaHCO3 instead of

replacing NaHCO3 as done by Indiana University Axolotl Colony.

As a more practical straight-forward alternative to making up your ownsolutions, you can purchase kits for adjusting the hardness of water at your local

aquarium outlet (they also directly adjust pH and are sold as such). If you want toget the salts for the solutions mentioned above and you have problems finding

them, I have seen them at the Chemistry Store, though I have never purchased

anything from that company.

Final WordsTo sum up, water conditions are an important consideration when keeping

axolotls. Remember to regularly replace 20% of the water each week. Depending on

the size of the aquarium or container, and whether or not it is filtered, thesechanges may need to be more or less frequent. Do occasionally test the water for

its different constituents and pollutants. Taking care of water conditions will helpto prevent disease outbreaks. It will also keep your axolotls healthy and

comfortable, and it will encourage breeding.


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Rearing Axolotls

IntroductionI first

bred

axolotlssuccessfully in the

late

1990s.Thankfully

I was verysuccessful

. Byfollowing

the advice

and

directionson thispage, you

should be

too.Axolotllarvae are

surprisingl

y tough,

as far asnewt andsalamande

r larvaego. By the way, "larvae" is the plural of larva, the term used to describe axolotls(and other newts and salamanders) that have yet to develop all four legs. Due totheir toughness, if we follow the guidelines on this page we shouldn't have any

major problems rearing the larvae.

We should bear in mind that there will always be a few casualities when

rearing large numbers of larvae. Some larvae will have "unseen" genetic problems,some will succumb to stress that others will survive, and some will just be plainunlucky. For the beginner, it is most advisable to attempt to rear only a few larvae

at a time. It's better to give away or, though it may seem unpleasant, cull most of

the eggs, giving the remainder all of your attention and resources, than to try torear many hundreds of larvae for the first time and see them all die due to

stretched resources, bad water conditions, or other problems frequentlyencountered by beginners. If you have too many eggs, you will find plenty of people

willing to accept them from you on the Caudata.org Forum. Likewise, if you are

looking for axolotl eggs or young axolotls, you will find them there too. Unusualcolours, like the melanoid axolotl larva we can see at the top of this pagedeveloping in its egg, are often available through the Forum.

Initial care of eggs


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Finding axolotleggs, or seeing a

female spawning,often occurs when

we least expect it,or at least not quite

on the day weexpect. It's always agood idea to keep aneye out for old

spermatophores in

the parents' tank so

that we have somewarning that theremay soon be many

new mouths to feed.

On finding eggs,we must decide if they are to be removed, or the parents are to be removed andthe eggs left behind. Many first time breeders opt for the latter choice, but axolotl

eggs are quite tough, so the eggs can usually be removed from a tank and moved to

another without issue. They can even be removed from rocks if you're careful: there

is generally a point of attachment to the egg's outermost jelly layer, which can besliced with a finger nail, thus freeing the egg. Each egg is surrounded by severallayers of jelly, so don't be too afraid. Eggs attached to plants are great, because

they will stick to the plants. The plants can be moved carefully to the new tank,

thus avoiding all hand contact with the eggs themselves.

Once you have made your choice (to move or not to move the eggs), it's time tomake sure we have correct conditions for the eggs to hatch. Pictured to the left is a

small aquarium (45x20x25 cm, 18x8x10 inch) solely for hatching eggs (I opted to

hatch just 100 in this case). Remember to use dechlorinated water. Water shouldn'tbe soft: do you get limescale in your water pipes or kettle? If you get limescale,your water isn't soft. If you're not sure, you should read theRequirements Page formore information about dissolved salts and their importance.

Our next concern is water temperature. Keeping the eggs at a warm

temperature (to an absolute maximum of 25 C /77 F) will cause the eggs to hatchsooner (generally in less than 14 days), whilst a lower temperature (such as 18 C /64 F) will result in them taking perhaps more than 20 days. Being able to

manipulate the time taken to hatch can be very useful if you need a while to secure

a food source for the newly hatched axolotls. By lowering the temperature you can

give yourself an extra week or two in order to acquire some brineshrimp eggs,culture your Daphnia, or order some microworms from a dealer.

Food


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Speaking of

food forlittle

mouths,it's time

weconsidered ouroptions. If

you bred

your

axolotlsdeliberately, the

chances

are youare

alreadysetup as

far as

providingtiny livefood

items is concerned. More often than not though, we need to acquire these food

items in a hurry. Newly hatched axolotl larvae can vary in size from 10-13 mm(roughly 0.5 inch). On hatching, they will still possess some egg yolk in their

stomachs (the white substance that should be quite visible to the naked eye). Untilthis is used up they will be motionless and won't require food.

Within 24-72 hours after hatching, they will require food. From this point until

they reach approximately 20 mm in length (a little under an inch), their diet mustconsist solely oflivefood items of a very small size. They will ignore dead food untilthey have grown significantly. This is because, instinctively, young larvae respond

to prey movement alone. It is not until later that smell will play an important role

in feeding. If you cannot meet this demand for tiny live food, your larvae will starveto death, unless they eat each other (very hard to do for newly hatched larvae). For

newly hatched larvae, the live food choices are: newly hatched brineshrimp(Artemia), smallDaphnia (see the photo on the right) or Moina,

and microworms (microworms are not ideal and won't be well received until the

axolotl larvae develop their front legs). There is an excellent article about tiny livefoods at the Caudata Culture web site, and I recommend you read that before

proceeding.

There is a good article about foods for newly hatched salamanders over at

Caudata Culture. Here's a link to that article.

My preference is to feed young Daphnia, with some microworms as back up. I

culture both, myself. I wouldn't recommend feeding wild-caught Daphnia or Daphnia obtained from an unknown source when feeding

axolotls, or even fish. They have been known to carry diseases if taken from nature

or sources containing other animals. Culturing your own, however, removes most ofthis danger, and although not as small or quite as nutritious as newly-hatched

brineshrimp (young Daphnia are approximately two and a half times the size ofnewly hatched brineshrimp), youngDaphnia are a good first food for axolotl larvae,

and they can be free! I feed mine on crushed trout pellets (the same ones I feed the

axolotls). The Daphnia don't actually eat the pellets but rather the bacteria thatgrow as a result of the leeching of nutrients from the pellets into the water.


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Microworms aren't the most nutritious food - axolotls fed solely on these will

grow very slowly, and won't be received well by larvae that have yet to develop

their front legs. They are a good food when you are in need though.

After Hatching

If you'd like to see a photographic diary of my first albino embryos as theydeveloped before hatching, then look at the Embryo Photo Series Page.

On hatching, most axolotl larvae are about 11 mm (less than half an inch) inlength. Just before hatching I normally lower the water level to about three or four

centimetres (an inch and a half) so that any daphnia in the tank are concentratednear the larvae for easy access. Once most of the larvae have hatched, it is a good

idea to tear the jelly coat of those eggs that haven't hatched yet in order to free

the larva inside. This can be done with a sharp forceps or narrow scissors that isinserted into the egg and then the prongs/blades are pushed apart.

As explained earlier, at this stage the larvae usually won't eat because they're

still absorbing the yolk from their eggs. You should be ready with your chosen first

food. I normally have some Daphnia in the tank a few days before hatching in order

to have lots of little tiny young Daphnia present when needed. The larvae can getair bubbles in their stomachs if not fed early enough, but these will be expelledonce they start to feed.

Very young larvae can be kept

together without much risk of cannibalismsince this really only begins once the

front legs develop. When very young theyshould be fed frequently (once or twice

daily). If kept at about 20 C (68 F) theyshould reach about 1.5 cm in length

within a week. The larva pictured on the

right is four days old and 14 mm inlength. It is D/D M/m a/a (seethe Genetics Page for more information

about colour). If feeding brineshrimp, at

least some of the water should be

replaced each day because newly hatchedbrineshrimp die quickly in fresh water andcan foul the water in a matter of hours.

As mentioned above, Daphnia will live in

the tank with the larvae until eaten, so

occasional water changes are fine (partialwater changes a few times a week).

Larvae never grow at the same rate,so it is advisable to divide them up

according to size once they begin toreach about 2 cm in length. At this sizethe larvae become more cannibalistic,

since they snap at anything that moves

and at that size can damage their siblings (missing limbs and gills are an obvious

sign). The larva below-left is a D/D m/m a/a sibling of the larva above-right but at7 days old. It is 19 mm in length.


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Cannibalism is a natural tendency, and studies

have been carried out on the cannibalistic variants

of salamander larvae. If left to cannibalise theirsiblings, they actually develop different morphology

(shape and appearance). This is most noticeable inthe shape of the head and the teeth. James

Petranka's Book, "Salamanders of the United Statesand Canada" discusses cannibalism in detail,especially in the case of the Tiger Salamander, withsome excellent photography, and William Duellman

and Linda Trueb's book, "Biology of Amphibians",

contains some excellent diagrams of the head

morphology of the different morphs of the tigersalamander, a close relative of the Axolotl (seethe Books and Links Page).

In young larvae, particularly melanoid albino

larvae like that on the left, you can actually see theliver, heart, stomach and intestines right throughthe skin. To minimise cannibalism, Peter Scott

recommends that the tank is heavily planted and

that light levels are lowered. A more reliable

method is to reduce the numbers as much aspossible in each container, but appetite does seemto decrease in low light.

It's been my experience that front legs begin to develop once the larvae reach

20 mm (within about 9 days of hatching at about 22 C) and the hind legs begin todevelop at the end of the third week. This all depends on temperature and feeding.The lungs first develop around the time that the rear-legs develop (yes, axolotls do

possess lungs as well as gills). As the larvae grow they need to be thinned out, and

any deformed or markedly inferior larvae (such as those that don't re-grow limbsand gills easily) should be euthanised/culled. There has been a lot of inbreeding inaxolotls over the many years they have been kept in captivity, and this means thatthe likelihood of defects and oddities developing is greatly increased in this species.

Using the conditions just described, at 7 days, I

still feed young Daphnia to the larvae, and most ofthe larvae are about 18 mm in length. At 9 days,most larvae have very noticeable front limb buds

and most are about 20 mm in length. This is a high

growth rate and I attribute it to the daily feeding of

young Daphnia and the temperature at which theyare kept (22 C).

The golden albino larva on the right is 10 days

old and is 22 mm in length. The arrow is pointing at

a limb bud. At this size they eatadult Daphnia (which are 2.5-3 mm in length). At25 mm (1 inch) I try to maintain a maximum of 25

larvae per 45x20x25 cm aquarium. Remember, if

you have too many larvae, either find new homes

for them or cull them to prevent disasters. At25 mm, hind leg buds should be quite apparent onmost larvae and some should have well-developed

front legs.

At this point it is possible to begin feeding thelarvae with thawed frozen bloodworm (see

the Feeding Page). These can replace partially, or


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fully, the small live foods you've been using up to this point. If you've been keeping

up with the appetites of the larvae, you will probably be running low on live food

any way.

The photo on

the left shows a 32

mm melanoid albinolarva (D/D a/am/m). At this stage

its front legs arealmost fully grown

and hind leg buds

are quite visiblefrom the side (not

visible in this photothough). Note the

lack of iridophores

(shiny pigment) inthis larva, due to itbeing homozygous

for the melanoid

gene m.

Xanthophores arealmost absent in this

larva, another effect of the melanoid gene.

At 36 mm, the colour phenotype of each larva is generally very apparent - this

means you can tell different colour types apart quite readily. The front legs are nowfully grown and the hind legs are growing.

At 40 mm (1.5 inches), the hind legs are about half grown. At this size,

cannibalism can be a noticeable problem, so do try to keep the numbers in each

tank at a low number (in the tank mentioned above, try to keep less than tens 40mm larvae together). Feet and gills will still regrow rapidly on larvae at this size,however the older they get, the slower regeneration occurs. Another fact to be

aware of is that wild type larvae tend to be more aggressive than non-wild types.

Wild types will also show a tendency to attack non-wild types rather than other wild

types.

You can use biofoam filters to try to reduce the number of water changes.These aren't great filters for animals like axolotls, but for larvae they are quite safe

(no risk of sucking up larvae). If you know what you're doing, you could use a

canister/external filter on a large aquarium. You will need to make sure that the

input is protected from sucking up larvae, and the output flow spread out so that itdoesn't stress the larvae (excessive water flow is a common cause of stress in

axolotls, leading to disease).

JuvenilesThe larvae in

the photo to the

right are about50 mm (2 inches) in

length. The hind legsare not fully grown

at this point but are

quite visible. At thissize they are morethan capable of


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taking the 3 mm axolotl pellets.

Once the hind legs are fully developed, the larvae are now miniature versionsof the adults, so they should now be called juveniles, or sub-adults. Growth should

be steady, and juveniles are quite capable of taking small pieces of earthworm (or

whole earthworms that are small in size).

If you find frozen bloodworm expensive and messy, it's worth knowing that atabout 2.5-4 cm (1-1.5 inches) most laboratories begin feeding with axolotl pellets.Be sure to gradually changes foods though, rather than doing so abruptly: it may

take a few days before the animals begin to take the "new" food.

If you would like to know more about the stages of larval growth, look at

the Biology Page. There is a nice diagram of the stages of axolotl growth, from eggto juvenile.

The photo below shows 15 cm (6 inches) juveniles of various colours.

Genetics and Colour

OverviewThe Axolotl is studied the world over for several reasons. All of the traits which

make it so suitable for study, as for all living things, are dependent upon its genes.

This page will attempt to give a brief overview of axolotl genetics, mainly from the

viewpoint of the hobbyist, who tends to be most interested in colour.

Axolotls have 28 chromosomes per cell, in fourteen pairs. Humans have 46

chromosomes in 23 pairs. A chromosome is a thread-like structure composed of DNA

and protein. The length of a chromosome is made up of many units of DNA called

genes. Each gene has a special place on a chromosome and the position which itoccupies is called the locus of that gene.


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When an axolotl reproduces, the sperm from the male (which contains 14

chromosomes) and the egg from the female (which also contains 14 chromosomes)

fuse to form the zygote, the first cell of the new axolotl. So each new cell of thisnew animal has 28 chromosomes. However, in the production of gametes (the sperm

and egg cells) via the process known as meiosis, small exchanges of parts of thechromosomes take place (known as "crossing-over"), as well as a random allotment

of chromosomes from the mother or father's own parents to each gamete (whichmeans a gamete could have 2 maternal chromosomes and 12 paternal, or any othercombination).

So when axolotls reproduce, each new larva is a genetically distinct individual,

different from its siblings and its parents. This is the essence of genetic variation.

An animal's genotype is what its genes "say" it is, and its phenotype is the result ofthe gene, its expression. Mutant animals are those with genes differing from what is

accepted as normal.

ColourThe colour of axolotls is dependent upon pigment cells called chromatophores.

These cells are melanophores (containing eumelanin, a black-brown pigment),xanthophores (containing carotenoids and pteridines, yellow and reddish pigments)

and iridophores (containing crystalised purines, which impart a shiny iridescence).

Each cell in an axolotl, as stated above, contains 14 pairs of chromosomes.

Every characteristic of the animals is coded for by genes on pairs of chromosomes.The genes for the pigment cells are inherited independently of one another, and

there is no known linkage to any other genes. So, each pigment type is coded for bytwo different genes, one on each of a pair of chromosomes. These contrasting genes

that code for the same characteristic are known as alleles. A pair of alleles iswritten like this: X/x. A capital letter means that gene is a dominant gene, as

opposed to the small letter, which means that gene is recessive.

For example, the allele that controls albinism could be found in an axolotl inone of the following combinations: A/a, A/A, or a/a. If the animal was A/a, becausea is recessive and A is dominant, the animal's phenotype wouldn't be albino, but it

would still carry the gene for albinism (since it has an "a"). Since it carries both "A"

and "a", it is known as "heterozygous". If the animal had the A/A combination, its

phenotype wouldn't be albino, and it wouldn't carry the gene for albinism (bothgenes being the same, it is called "homozygous" for "A"). If it were homozygous for"a" (i.e. a/a), the animal's phenotype would be albino. Since "a" is recessive, both

alleles need to be "a" in order for albinism to be expressed in the phenotype.

Albinism results in a lack of eumelanin (the dark pigment). In axolotls, it also results

in an increased number of xanthophores (yellow pigment cells).

In the same way that a/a results in a lack of eumelanin, m/m (melanoid)

results in a lack of iridophores. Such animals are very dark, with no reflectivepigment cells at all. M/m or M/M would result in normal iridophore development.

Animals homozygous for "ax" (i.e. ax/ax) are axanthic, meaning they have no visiblexanthophores or iridophores. Such animals are almost as dark as melanoids. Animalshomozygous for both the albino gene and the axanthic gene appear to be slightly

off-white (yellowish). The following table summarises the colour genes.


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You may have noticed the "d" gene. This gene is a developmental mutant and

not a pigment mutant like the others. Animals homozygous or heterozygous for "D"

produce large numbers of yellow xanthophores. In combination with melanophores,

we get the wild type colouration (dark brown/olive-green). However, in animalshomozygous for "d", the normal pigment cells are produced, but they never migrateoff the neural crest of the embryonic animal, resulting in the white phenotype. It is

important to realise the this animal is not albino. This phenotype is white, but has

dark eyes. It is known as leucistic. Simple albinism in axolotls leads to a

yellow/golden animal, with red/pink eyes. In order to produce a white albino, theanimal must have the d/d genotype in combination with the a/a genotype. Melanoidalbinos (m/m with a/a) are also white animals with pink/red eyes. This can make

initial identification of a white albino's phenotype difficult to determine for the

novice.

Colour typesHere are photos and descriptions of some of the commonly available colour

variants and an explanation of the genetics behind them.

Wild Type

Wild types vary somewhat in exact colour, but are generally a shade of darkbrown with black, yellowish, and shiny patches/speckles. The phenotype of wild

type animals is dark, non-melanoid, non-albino and non-axanthic. In the photo

below, the animal on the right is a wild type female. This is the typical wild typeappearance. You may also encounter tan or very lightly speckled variants. Wildtypes are not homozygous for any of the colour mutations.


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Melanoid

In the above photo, the animal on the left is a female melanoid. As describedearlier, melanoids lack the "shiny" pigments (crystalised purines). The amount of

yellow present is also much reduced. In contrast, the number of melanophores (dark

pigment cells) is greatly increased, resulting in a black animal. The easiest way todetermine if an animal is melanoid or a dark wild type is to look at the eyes: non-

melanoids have a shiny ring around the pupil of the eye, while melanoids (andmelanoid albinos) do not. Melanoids are homozygous for "m" only (i.e. m/m), but

they may be heterozygous for other colour mutations.

White (also called Leucistic)

Commonly known as leucistic, the phenotype is d/d, non-melanoid, non-albinoand non-axanthic. Here's a picture of a large adult female. Notice the black eyes

and small number of melanophores on the head and back which indicate that it isnot an albino. White axolotls with black eyes are not albino. While d/d prevents the

axolotl's pigment cells from migrating off the top of the animal, this does not


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necessarily mean that all leucistics will possess colour cells on the the head and

back - look at the eyes to be certain.

Albino

Phenotype is albino a/a (lacking melanophores). There are many kinds ofphenotypically-different albino axolotl. Here are some of them. The first is the

golden albino (D/D a/a orD/d a/a). It has normal migration of pigment cells, butlacks melanophores, hence the yellow/gold appearance.


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The second kind of albino I will mention is the axanthic albino. It has normal

pigment cell migration but is homozygous for the albino gene and the axanthic gene(a/a and ax/ax), meaning it lacks melanophores, xanthophores and iridophores. It is

almost white, but becomes yellow with age due to the accumulation of riboflavinsfrom its diet. Here's a picture of one of the former Indiana University Axolotl

Colony's albino axanthic specimens

The third kind of albino is the white albino. It is homozygous for "d" and "a"

(d/d and a/a). The photo below is one of the former Indiana University AxolotlColony's white albinos. Note the presence of iridophores (shiny pigment cells) in its

gill branches.


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The fourth kind of albino that I will discuss is the melanoid albino. It is

homozygous for "m" and "a" (m/m a/a). This is a male axolotl. While a non-albino

melanoid would be black, the combination of melanism and albinism "removes" allpigment except a tiny hint of yellow xanthophores on the head and back.


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ConclusionAxolotls come in many different colour variations. Axolotl breeders often

produce an odd offspring whose phenotype defies what the breeder knows to be its

genotype. Piebald axolotls (not just on the top of the body like a leucistic), yellow

leucistics with black spots, and the harlequin (orange and black patches on a whiteaxolotl) are just a few examples of what chance can present. You can see the hugevariety of axolotl colour variations in Caudata.org's User Photo Gallery.

Documents

The Axolotl is unusual in nature because it retains its larval form into adulthood.pdf