The Axolotl is Not a Fish
Ambystoma tigrinum
By David Rentz
First published in Tank Talk, Canberra and District Aquarium Society, Australia
Aquarticles
From time to time I see axolotls for sale in Australian aquarium shops and frequently
they are labelled "walking fish." They are not fish at all but amphibians called
salamanders, related to frogs and lizards. It is easy to understand the reason for the
misnaming; there are no salamanders native to Australia and the axolotl is probably the
only salamander the average Australian will ever see alive. There are some interesting
biological characteristics about axolotls which are worth noting here.
The peculiar word axolotl is an Aztec word, probably one of the few in use in our
language. It is a species of salamander known as the tiger salamander, Ambystoma
tigrinum. This species has a very broad distribution for a salamander. It occurs in
Western North America and extends South into Mexico, hence its association with the native
Aztec people of central Mexico. The axolotl is a peculiarity in the normal life cycle of
the tiger salamander as you will read.
Normally the tiger salamander follows a conventional pattern in its life history.
Adults are terrestrial. A migration of males and females to the breeding ponds occurs in
late winter. Certain sites are the scene of courtship activity and mating. The eggs are
not fertilised as they leave the female's body but males deposit lumps of a gelatinous
substance tipped with a whitish ball containing hundreds of spermatozoa on the bottom of
the pond. The female crawls over this 'spermatophore,' takes up the fertilising tip, then
within her body the eggs are fertilised and they are laid within a few hours.
The larvae are small and have bushy gills. They resemble a tadpole with feet. By autumn
they are full-sized and ready to leave the water and take up life on land. The gills
shrink and lungs develop, the tail also undergoes a change. The tiger salamander then
begins its life on land. This is typical of many salamanders. They are predators and eat
insects, snails, slugs and any other small creatures, including salamanders, that they can
find.
How the axolotl comes about is an interesting part of this story. In the highland lakes
of Mexico and the Rocky Mountains the salamander larvae never change into adults. They
grow to adult size but remain aquatic retaining gills and a large fin-like tail. This is
termed "neoteny" and it was this form that the Conquistadors of Mexico found and
learned the Aztec name axolotl. The sexes breed in water and the larvae develop into
adults and remain there (but the chain may be broken).
The neoteny described above is triggered by cold water. If the water becomes warm or
some other factor occurs (like a nice terrarium) that seems favourable towards a
terrestrial existence, the axolotl will emerge from the water and become a land-loving
creature. Once this happens, it cannot be reversed.
Axolotls like deep, cool water. During a Canberra summer, they should be moved to an
air-conditioned room or a few ice cubes should be placed daily in their tank. In captivity
axolotls do well on unwanted fish but will also thrive on pieces of meat, fish, prawns and
earthworms. An albino form is often available but remember that all albino forms of
animals suffer discomfort under strong light. And with axolotls, remember to keep the
water cold.
See also: Breeding the Axolotl - Ambystoma mexicanum, by
Andrew and Julie Boyd
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