Species name: Ambystoma mexicanum
Common name: Axolotl, Water dog, Mexican Salamander
Maximum size: Usually 10-12 inches (25-30cm), sometimes much larger
Environment: Cold, freshwater lakes in Mexico
Origin: Native to the high altitude Lakes of Xochimilco and Chalco in central Mexico, these amphibians are under great threat in the wild. Fortunately they are a hardy captive species and very useful in research for their extraordinary regeneration abilities, which is why their numbers are so high in captivity. Their external gills, tails, and legs can all be regenerated if damaged or removed.
Temperament: Axolotls will eat tankmates small enough to be eaten whole. They may grab at fish too large to be eaten whole and damage fins and other body parts.
Company: Their external gills prove to be too irresistible to most fish. Many fish are simply too small to be housed with axolotls. Axolotls are best kept in species only tanks with axolotls of similar size, this will provide the minimum risk of damage.
Water parameters: Temperatures in the low 60s Fahrenheit (16-19 Celsius) are ideal. They can tolerate temperatures up in to the low 70s (about 22 Celsius). Above this and stress can lead to a quick death. For axolotls pH is not too important as long as it is not extreme. High water quality must be maintained at the same level as aquarium fish, so ideally nitrates should be maintained at no more than 20ppm.
Aquarium setup: Since they will roam the bottom, only using the rest of the tank for the occasional trip to the surface for a gulp of air, a large footprint is desirable over extra height. Open areas to roam along with places to hide will serve the axolotls well. PVC pipe connectors serve as an ideal shelter because they are smooth and will not damage the axolotls, come in various diameters to fit any size axolotl, are cheap, easy to clean, and will host green algae to cover their bright white appearance. Live plants can be used to help maintain water quality and serve as a good natural accent to the tank. They can be dirty, as would any animal of their size, and therefore require ample filtration and water changes. Canisters as well as good hang-on-back filters will do very well. High flow can cause stress, evidenced by forward pointing gills and a sideways curled tail, so these need to be looked for. To alleviate this spray bars on canisters can be used to diffuse the flow of the filtration. Although they can breathe atmospheric air, it is good to keep the oxygen levels up in the tank for the axolotls and the nitrifying bacteria keeping their water clean, so an air pump with air stone is recommended. Sand is the ideal substrate. Gravel can be ingested and can block their digestive tract. Bare bottom provides no traction, which long term can become stressful for them. Sand is good because it will keep debris in the water. With enough flow the debris will keep moving until it gets to the filter. Sand will not trap debris the way gravel will, which can lead to water quality issues. Sand is also more natural.
Feeding: Axolotls are carnivorous. A high quality diet is vital for them to thrive. This is best achieved with high quality pellets. Most commonly used are soft, sinking trout chow pellets. Some high quality aquarium fish foods have been shown to also provide a complete and balanced diet for axolotls. Some keepers include small strips of various meats, but these can lack the micronutrients and trace elements found in high quality pellets, are nutritionally imbalanced, and are unnecessary. As with any carnivores, many choose to feed live foods. This should be avoided because they carry the same risks as feeding them to fish in that they can introduce many pathogens, increase aggression, and are nutritionally incomplete. Feed foods that can be swallowed whole.
Breeding: Axolotls can be sexed by looking at the genital area. Males have a noticeably swollen cloaca while females have a smoother appearance to the area around the cloaca. Stimulating mating is done in ways similar to many fish. By simulating seasonal changes they would experience in the wild (photoperiod, changes in temperature, etc.) they will be triggered to breed. By shortening photoperiod followed by increasing it again or slightly raising the temperature followed by dropping it (simulates onset of rainy season) you can mimic these natural events. The male will deposit spermatophores (packets of sperm) on the bottom of the tank and then lead the female above them at which point she will pick them up with her cloaca. Later she will lay the eggs individually, preferably on plants (fake are fine, they are easy to remove from the tank and will not rot). The eggs can be reared in a separate tank. After a couple weeks they will hatch and the offspring need to be fed live foods as would be done with many fish with very small fry. Later they will accept non-living food items.
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