Care
The Axolotl is a neotenic salamander that originates from Lake Xochimilco and Lake Chalco in the Valley of Mexico, a highland plateau in central Mexico. Unfortunately, Lake Chalco is no more, as it was artificially drained to avoid periodic flooding and to provide for land expansion. Lake Xochimilco still exists, but only as a shell of its former self, present mainly as a network of canals, many heavily polluted. As a result, this species is critically endangered in the wild; however, it is captive bred in large numbers at numerous aquaculture facilities and specimens for sale in the shops are all bred and raised in captivity. Unlike their wild counterparts, pet strains also have some input from Tiger salamanders (A. tigrinum) which introduced colours previously unknown in this species. Fortunately conservation organisations are working with pure strains and our hobby animals are never going to be used to repopulate wild habitat. Axolotls are neotonous, in that they reach maturity without undergoing metamorphosis, remaining in their aquatic form. Odd individuals may display a trait inherited from their tiger ancestors and leave the water to become mole salamanders, otherwise this is something that only occurs when an axolotl is exposed to poor water quality.
Axolotls do have some specialist care requirements when it comes to keeping them in the home aquarium. Firstly, substrate choice is very important - they should not be kept on gravel, as there is the very real risk of them ingesting pieces of substrate when lunging for food (this can lead to internal problems). Sand is much softer against their skin and does not pose any problems when they feed, passing freely from both ends. Filtration should be efficient, but water movement very gentle. Internal sponge filters are ideal for the Axolotl tank as they provide filtration and aeration without being too vigorous. If an external canister is used, it would be prudent to place a coarse sponge or filter bag/mesh over the intake pipe cage to prevent the Axolotls from being drawn against it and subsequently trapped by the flow. If there is too much water movement in the aquarium, the Axolotl's gills may curl forward, so be sure to reduce your flow if this occurs. A means of chilling the water may be necessary during particularly hot summers, as a prolonged water temperature above 24 °C will cause stress followed by illness and death. Gill size can vary with temperature, as oxygen content will be lower at the upper end of their tolerance, making larger gills necessary. At the other end of the scale, cold does not especially bother them and they thrive when given seasonally low temperatures. Hiding places should be provided amongst smooth rocks, driftwood, PVC pipes, and hardy aquatic plants. Regular partial water changes are essential as Axolotls require excellent water quality at all times and will not tolerate a build up of nitrate. With regards to compatibility, Axolotls will attempt to prey on anything they can fit in their mouths, including fish that are of similar size to themselves, so they are best maintained in a species-only environment. They can pose a serious risk to each other as well though. Smaller/younger Axolotls are easy targets for larger individuals and these may lose limbs or even be eaten. Fortunately, these animals can regenerate lost limbs and such injured individuals respond well to improved husbandry. When keeping a group of Axolotls, be sure to provide adequate space and ensure there are plenty of hiding places (several per Axolotl) and visual barriers amongst the decor. It is important not to overcrowd them and make sure all individuals are of approximately the same size. Axolotls are available in a selection of different colour forms. The standard 'wild type' is an olive grey colour with dark spots and gold speckling. Albino, axanthic, leucistic, and melanistic varieties are also readily available, and a rarer striking black and white piebald variety is highly sought after. As with other salamanders, the Axolotl is capable of regenerating lost limbs over a period of a few months and their immune systems function well at the colder end of their preference.
Feeding
Carnivorous. Offer a variety of foods including sinking pellets/granules to ensure a diet rich in essential vitamins and minerals. Meaty frozen foods such as white mosquito larvae, bloodworm, daphnia, vitamin-enriched brineshrimp, mysis shrimp, chopped krill/prawns are all suitable for animals of varying sizes and earthworms are a favourite treat.
Breeding
Axolotls breed readily in the home aquarium. They can be triggered into doing so by providing a seasonal drop in temperature, after which they'll spawn naturally or often simply by performing a reasonably sized water change. The adults will predate the eggs, so you will either need to set up a separate breeding aquarium for this purpose, or have a spare tank ready to move the adults into once the female is spent of eggs. A breeding tank should have some flat pieces of slate on the base for the male to deposit his spermatophores (packets of sperm) onto, and aquatic plants for the female to deposit her eggs. Spawning is initiated by the male, who performs a courtship dance, swimming around, raising his tail and writhing excitedly. The male deposits a number of spermatophores around the tank, and then nudges the female's vent and leads her around the tank, escorting her in the right direction and encouraging her to pick up the spermatophores with her cloaca. Fertilisation takes place internally, and a few hours later, she will lay the fertilised eggs on the aquatic plants. Once the female stops laying, she and her partner should be moved to another aquarium to prevent predation. The eggs should hatch after 2-3 weeks (temperature dependent) and the young, measuring 10-13mm, will require tiny foodstuffs such as baby brineshrimp once they have used up their yolk sacs. Unfortunately cannibalism tends to be rife, and several rearing tanks may be needed so that low numbers (less than 10) can be kept in each tank, separating them into groups by size. Lowering the light level and providing dense planting is also said to help minimise cannibalism.
