Axolotls are amphibians that remain fully aquatic throughout their lives. Often called “Mexican walking fish” due to their appearance, these fascinating creatures are a type of salamander. Unlike most amphibians that transition from water to land, axolotls possess specific biological traits allowing them to thrive exclusively underwater.
Fully Aquatic Adaptations
Axolotls possess distinct physical characteristics for their fully aquatic lifestyle. Their most recognizable features are external, feathery gills, essential for extracting oxygen directly from water. These gills are richly supplied with blood vessels, maximizing the surface area for efficient gas exchange. Axolotls also have a finned tail, which aids their movement. Additionally, their thin, permeable skin allows for cutaneous respiration, absorbing oxygen directly through their skin.
Their Natural Habitat
The natural home of the axolotl is the ancient lake system of Xochimilco, located near Mexico City. This environment is characterized by cool, slow-moving, or stagnant waters rich in oxygen. Historically, axolotls also inhabited Lake Chalco and Lake Texcoco, which have largely disappeared due to urban development. The axolotl is classified as critically endangered in the wild, with numbers dwindling over recent decades. Their decline is primarily due to habitat loss from urban expansion, pollution, and the introduction of invasive species like carp and tilapia that prey on young axolotls and compete for food.
The Unique Trait of Neoteny
The reason axolotls remain aquatic throughout their lives lies in a biological phenomenon called neoteny. Neoteny refers to the retention of larval characteristics into adulthood, where an organism reaches sexual maturity without undergoing metamorphosis. Axolotls do not naturally transform into a terrestrial adult form. They maintain their external gills and aquatic body shape while becoming reproductively mature. This occurs because they lack the thyroid-stimulating hormone needed for the thyroid to produce thyroxine, the necessary component to initiate metamorphosis. While metamorphosis can be artificially induced in laboratory settings using hormones, it is not their natural life cycle in the wild.
Creating an Ideal Aquatic Environment
For those keeping axolotls, understanding their aquatic needs is important. Axolotls require cool water temperatures, ideally between 15.5°C and 18°C (60-65°F), as warmer water can cause stress and health issues. The water pH should be maintained between 6.5 and 8.0, with an ideal range of 7.4-7.6. Proper filtration is essential to manage the waste they produce, keeping ammonia and nitrite levels at zero and nitrates below 20 ppm. All water used must be dechlorinated, as chlorine and chloramine found in tap water are highly toxic to their sensitive skin and gills. A tank size of at least 20 gallons for a single axolotl is recommended, with larger tanks providing more stability and space.