Axolotl (Ambystoma mexicanum)
The axolotl (Ambystoma mexicanum) is an amphibian species belonging to the order Caudata (salamanders) and the family Ambystomatidae, and it is native to Mexico. Known as the "walking fish" or "water monster," axolotls are rare organisms that remain in their larval stage throughout their life. The species is classified as critically endangered.
Axolotl (Unsplash)
Morphological Features and Neotenic Life
Axolotls are known for retaining larval characteristics even as adults. This phenomenon is called neotenic development, meaning they remain in aquatic environments and continue to respire through external gills. These external gills, located on either side of the head, are prominent and have a reddish color. Their average length ranges from 15 to 25 cm, though some individuals can grow up to 30 cm. Their bodies are flat, and their tails are long and sail-like.
Axolotls can also breathe through their lungs and exchange oxygen through their skin. They have a long body with a dorsal fin extending from the back to the tail, webbed tails, and webbed feet. These features provide them with strong swimming abilities. In their natural environment, their coloration is usually brown or gray, but genetic variations in laboratory environments have led to the development of albino, leucistic (pink-eyed white), and golden forms.
Another distinctive morphological feature is the constant upward tilt of their mouths, which gives axolotls a permanent "smile." Additionally, their large eyes are exposed without eyelids. They capture their prey by sucking it in with a rapid vacuum motion, which makes their hunting style highly effective.
Habitat
Axolotls' natural habitat is found in the lakes of Xochimilco, Chalco, and Chapultepec around Mexico City. These areas have been heavily degraded due to pollution, invasive species (especially tilapia and carp), and habitat loss. Lake Chalco has largely dried up, Xochimilco exists only as a canal system, and Chapultepec Lake is an artificial lake lined with cement where released axolotls breed.
Feeding and Reproduction
In their natural habitat, axolotls are carnivorous and occupy the higher levels of the food chain. Their primary food sources include small fish, crustaceans, mollusks, insect larvae, and various invertebrates. They face food competition from invasive species like tilapia and carp, which disrupt their natural feeding patterns and reduce their survival rates. They capture their prey by suction, allowing them to catch it with swift, sudden movements.
Axolotls breed in aquatic environments and typically at temperatures ranging from 14–20°C. Reproduction usually begins in the spring. Male axolotls perform a "courtship dance" by vibrating their tail and the lower part of their body to attract the female. Then, they deposit a spermatophore (sperm capsule) on the bottom of the water. The female collects this spermatophore through her cloaca and internal fertilization occurs.
Females lay approximately 100 to 1,000 eggs on plant surfaces or rocky structures. These eggs hatch in about two weeks, and the larvae begin free swimming. Upon birth, the young are not cared for by their parents and must survive independently.
Swimming Axolotls (Unsplash)
Conservation Status
The axolotl (Ambystoma mexicanum) is classified as "Critically Endangered" by the International Union for Conservation of Nature (IUCN). Over the past three generations (approximately 16.5 years), the population has decreased by over 80%. In the 1990s, thousands of axolotls could be found per cubic meter in the canals of Xochimilco, but in 2013, only a few individuals were found during sampling.
The main threats to the species include habitat loss, urban sprawl, agricultural and domestic pollution, the excessive growth of invasive species (like tilapia and carp), and illegal pet trade. Furthermore, the axolotls are now surviving in isolated populations due to the drying and pollution of their habitats in Xochimilco and Chalco.
Various local and international efforts are being made to conserve this species. The Mexican government and researchers have established axolotl shelters on artificial islands known as "chinampas," which are compatible with traditional farming practices in Xochimilco. These structures provide safe spaces for axolotls and also help improve water quality, contributing to the restoration of the habitat. Initial observations have shown significant improvements in water quality and an increase in individual weight in these shelters.
Research Significance
Axolotls are notable for their regeneration abilities. They can regenerate their heart, spinal cord, brain tissue, eyes, jaw, and even limbs when lost. Due to these capabilities, axolotls are used as model organisms in stem cell research, tissue engineering, and organ repair.
Scientists are working on understanding the molecular mechanisms of regeneration in axolotls and identifying the signaling pathways involved in the process. Specifically, experimental setups such as the "Accessory Limb Model" are used to investigate the signals that trigger regenerative responses in injured areas. These studies provide valuable insights into how regenerative capacities can be stimulated in humans.
Additionally, the axolotl's large genome (approximately 32 billion base pairs) and robust DNA repair mechanisms make them a valuable resource in cancer research and genetic engineering.
