The Axolotl Is Not A Fish By David Rentz

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 it's 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 females 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.