Axolotl is a Mexican salamander, or Mexican walking fish. It is closely related to the tiger salamander. They are unusual in that they reach adulthood without going through a metamorphosis. Instead of developing lungs and taking to land, they remain aquatic and gilled. Due to urbanization of Mexico City and pollution, they are Critically Endangered. The axolotl is also used extensively in scientific research due to their ability to regenerate limbs.