Axolotls (Ambystoma mexicanum)
 Literally,
the name "Axolotl" means "water dog,",
in Nahuatl, the language of the ancient Aztecs, although it can apparently
be translated a number of ways. "Water sprite" and "water
player" are just a couple. The axolotl takes its name from Xolotl,
the rather diverse Aztec god of games, monstrosities, and the dead and
resurrected. Axolotls come in many colour varieties. Grey, tan, brown,
white, golden albino, white albino, blue, as well as other varieties,
such as the black melanoid. The normally coloured or "wild type"
can come in anything from near-black, to chocolate brown, to almost cream
in colour and anything in between. There are even "piebald"
axolotls known as "harlequins". Prior to the growth of Mexico
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. 
The Axolotl is a fascinating creature for a number of reasons, including
its grotesque appearance, its ability to regenerate, and primarily the
fact that it exhibits the phenomenon known as neoteny. Ordinarily, amphibians
undergo metamorphosis from egg to larva, and finally to adult form. The
axolotl, along with a number of other amphibians, remains in its larval
form, meaning that it retains its gills and fins, and doesn't develop
the protruding eyes, eyelids and characteristics of other adult salamanders.
It grows much larger than a normal larval salamander, and reaches sexual
maturity in this larval stage. Another term to describe this state is
"perennibranchiate". It is completely aquatic, and although it does possess
rudimentary lungs, it breathes primarily through its gills and to a lesser
extent, its skin. It is generally accepted that neoteny is a "backward"
step in evolution, because the axolotl is descended from what were once
terrestrial salamanders like the closely related species, the Tiger salamander,
Ambystoma tigrinum (in fact, one theory suggests that the Axolotl
is in fact a Tiger salamander off-shoot, as it can interbreed with that
species quite successfully). Through some quirk of nature, a neotenous
form developed and, probably due to environmental conditions, prospered.
Neoteny is sometimes found in other amphibians, but tends to be caused
by low levels of iodine (an essential element in the making of thyroxine
hormones, essential to growth and development), or random genetic mutation.
In the axolotl the condition is totally genetic. When treated with hormones,
the axolotl will usually begin to metamorphose, but in very rare cases
it will metamorphose spontaneously.
How long do they live?
The average lifespan seems to be ten to fifteen years, although there was
at least one that reportedly lived twenty-five years in a French laboratory.
 Axolotl
Food
How Do They Find Their Food?
Axolotls find there food by smell and by their lateral line organs, which
are sensory organs located along the sides of their head and trunk. Axolotls
have weak eyesight and they do not seem to be used for finding food. Their
lateral line organs detect motion and pressure. When food is dropped from
the top, they use their lateral line organs and sense of smell to located
the food. If they happen to miss it, they will usually use their nose
to find food on the bottom of the tank. Non-live food should be siphoned
or netted out at the end of each day as not to spoil the water. It is
important to note that axolotls will eat or try to eat anything that is
put in front of their faces.
Juveniles should be fed every day with Artemia and adults every
other day with fish pellets, guppies, worms, or whatever you choose. Adults
can survive on once to thrice a week feedings. Some axolotls have different
metabolisms and might not eat for months and survive and even not exhibit
any weight loss. Before you feed your axolotl, make sure it's awake by
lightly tapping its container or turning on the lights or something that
will solicit a reaction.
Food
Overfeeding is not a known problem with axolotls, but make sure you clean-up
any uneaten food immediately. I mainly feed my axolotls frozen bloodworms,
worms or soft ground pellets made of fish. They are very odoriferous and
soft so they can sense them easily. They are soft and sinkable, which are
the key elements. When the food falls near them they open their mouth and
sucks the food in. They grip the food with their tiny teeth while they bolt
the food into their mouths. They can be trained to be fed in a certain area
for easy cleanup.
Axolotls love tubifex worms, they are a special treat you should offer
them occassionally. I would not put the worms in a tank with gravel or
rocks, since they tend to hide between them. You can also transfer your
axolotl to a clean container for feeding. Axolotls show no mercy when
they sense live food, be it a guppy or a worm. Brine shrimp are good for
juvenile axolotls, but tend to be messy and foul up the water since they
are raised in salt-water. They only last a few hours in a fresh water
tank, so take heed if you use them. Goldfish are harder for the axolotls
to catch than a guppy.
When You Are Away
Guppies are perhaps the best companions and food source for the axolotls.
They will not attack the axolotl, and they usually stay in the upper water
column. The axolotls will either float to the top and wait for them, or
they will patiently wait for the guppies to swim on by. They are an excellent
way to feed your axolotl if you go on vacation and cannot feed them fish
pellets.
Problems With Live Food
When you buy live food at a pet shop, you can sometimes get more than
you bargained for. fungal infections and bacterial infections can sometimes
be passed on to axolotls from the tubifex worms, goldfish, and guppies
that have been purchased from pet shops. I would recommend that tubifex
worms be thoroughly rinsed and kept in a holding tank for a few days before
given to the ajolotes.
AXOLOTL
HABITAT
Tank Setup
 At
a minimum, one juvenile axolotl will do fine in a 20 litre tank. The carrying
capacity for a standard 40 litre tank would be three adults. The height
of the standard fish tank is overkill for axolotl keeping. Therefore,
keep the water level at 60-70% volume. Axolotls naturally come from a
series of Snow-melt fed lakes southeast of Mexico City. So a tank kept
at room temperture is fine, the problem is sometimes keeping the tank
cool enough for them. Keeping the water cool is a main priority. Axolotls
in their native habitat live in temperatures of 15-20ºC with a pH
between 7.4-8.2.
The recommended temperature for keeping an axolotl is from 14-18ºC.
Since the axolotl is a cold-blooded animal, its metabolic rate is proportional
to its body temperature. When the water is unusually cool, it may take
an extra long time for the axolotl to digest its food. If it takes
too long, the food in the axolotl's stomach may begin to spoil before
it's fully processed. To avoid this sort of poisoning, the axolotl will
regurgitate its food at the first indication that spoiling may occur.
If your axolotl spits his food back up, first make sure that what you're
feeding it is fresh. Next, check the water temperature and make sure it's
not too cold.
Artificially Induced Metamorphosis
Laboratory experiments have been done to see whether axolotls use metamorphosis
to deal with environmental change. Axolotls that have the genes to undergo
metamorphosis can be readily do so with an injection of T4 thyroxin. Thyroxin
is a hormone that causes maturation in most vertebrates. Forcing natural
metamorphosis by reproducing drought conditions, increasing salinity, et
cetera, have been largely unsuccessful. For some axolotls, thyroid metamorphosis
is impossible. Other axolotls, who have the capability to transform, can
do so in under a month by being immersed in solution of triiodothronine
(T3). Other methods included the introduction of thyroxine (T4) or thyrotropin
hormones (TSH) into the axolotl.
Precautions
If you use a filter, make sure that the intake tube is hidden behind rocks
or somewhere their gills will not get sucked into. Most people use gravel
on the bottom of their tanks. This is not recommend, because they have a
tendency to swallow the gravel during feeding sessions. If you must use
river rocks (2.5cm - 4 cm in diameter). They are very smooth, and the axolotls
use them to rest or stand up upon.
If you want to have your axolotl share the same tank with other fish or
snails - DON'T. Don't give in to the temptation.
There are many reasons:
- Axolotl gills are incredibly tempting bait to fish and other water-dwellers.
The gills are very fragile and sensitive- even a little nibbling could
be harmful.
- Snails can be very harmful to an axolotl. Snails can overcome an axolotl
when it goes to sleep and suck away its flesh, leaving severe wounds
if not killing it.
- Axolotls have a big mouth, and if a fish or anything else comes too
close, it will be sucked into the axolotl's mouth and eaten.
Accordingly, it is recommended that you only
keep an axolotls in an aquarium with other axolotls.
 Lighting
and Cover
Axolotls are more mostly nocturnal; they do not like a lot of sunlight,
and should have a place to hide when it gets too bright. For baby axolotls,
cover the top of the tank with a dense array of plastic plants, without
the base. This allows the plants to bunch up and form a network on the upper
water column. The young axolotls float up to the plants, and stay in the
protective cover until it is feeding time.
AXOLOTL HEALTH
Anatomy
 Axolotls
typically have about 50 vertebrae. The tail region accounts for 70% of them.
Here is a diagram of an axolotl skeleton, side view. The lower and upper
jaw of the axolotl contain fine teeth. However these teeth are used for
gripping, as opposed to chewing. Digestion usually takes two to three days
to occur.
 Handling
Try not to handle your axolotl unless you have to. Axolotl skin
is very sensitive and soft, and even brief contact can be damaging if
you're not careful. About the only time you should have to handle you
axolotl is when you are moving it from one tank to another. If you suddenly
find your finger inside an axolotl's mouth, wait patiently for it to let
go. Do not fight the axolotl, or you may cause it harm. Their teeth are
harmless and it is quite amusing to watch the axolotl wrestled then spit
your finger out.
Size
Hatchlings are about 1 - 2 cm in length. Adults can get around 20 - 30 cm
length and weigh over 300 grams. Mature females are rounder in the abdominal
region, because they are filled with eggs. Their cloacas are smaller than
the males. Males are slimmer, and their cloacal region is larger because
there are jelly glands on both sides of the opening. Sexual maturity is
reached anywhere from nine months to two years.
Sex
Males mature sooner than females. Accurate sexing is easily done with mature
animals, not immature animals. Factor that influence growth rate: temperature,
amount of food fed, and amount of toxins in water. A good estimate of life
span in captivity is about fifteen years. There is no data on wild stock
but the assumption is that it would be less. Reproductive capabilities slow
down after five to seven years for females and eight to ten years for males.
Chemical Toxicity
Like fish, axolotls are prone to ammonia toxicity. This includes too much
ammonium, nitrate or nitrite in the water system. Symptons of this include
the attack of the skin of the external gills, cloudy eyes, and visible
infection on the skin of the animal. Chlorine, chloramine, pH, heavy metals
and TOC's can all be brought under control. However, ammonia, ammonium,
nitrate, and nitrite can suddenly change levels in the axolotls housing
and must be routinely monitored and brought under control. Also O2
levels can change suddenly and dramatically. If you suspect any health problems
for your axolotl, immediately replace the water with clean water (dechlorinated,
deammoninated and dechloraminated). Never use deionized water since they
do not contain essential minerals that the axolotls need. It is a good idea
to save some of the water, so that you may run a water test on it. Most
aquarium stores will run an ammonia and pH test for you, free of charge.
Regeneration
Axolotls are well known for their ability to regenerate body parts. They
are able to regenerate their gills, limbs, tail, damaged skin tissue, heart,
liver, kidney tissue, parts of their peripheral nervous system, and parts
of their central nervous system. Time of regeneration is a factor of age
versus time. A two inch animal might regenerate an entire limb in a month,
while an adult may never regenerate a lost limb but will regenerate quickly
damaged skin tissue. Adults should regenerate the entire tail, skin, muscle
and all, but it will take a few months.
AXOLOTLS GENETICS
As of 1990, there have been 44 mutant genes identified, affecting stages
of development from oogenesis to pigmentation. For the keeper who is keeping
an axolotl as a pet, as opposed to laboratory research, the different
colors of the axolotl or its phenotype is usually of core interest.
| Phenotypes |
Chromatosphores |
Albino - Deficient pigmentation in the skin. Animal
lacks melanosphores
Melanic - Extra or excess black pigmentation in the skin
Xanthic - Yellow pigmentation caused by hydrolysis of guanine. |
Iridosphores - Produces shiny iridescence
Melanosphores - Produces the dark pigment
Xanthophores - Produces the yellow pigment. |
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