The axolotl (Ambystoma mexicanum) is a unique amphibian species and a type of mole salamander native only to a few lakes near Mexico City. This creature is famous for its neoteny, a state where the adult retains juvenile features, remaining fully aquatic with external gills throughout its life. Despite being nicknamed the “Mexican walking fish,” the axolotl is not a fish, and the direct answer is no, it does not have scales. Its skin is soft, smooth, and highly specialized, reflecting its evolutionary path as a permanent water-dwelling salamander.
Amphibian Skin vs. Scales: The Biological Difference
The reason axolotls lack scales lies in their classification as amphibians, a group of vertebrates distinct from reptiles and fish. Scales serve a primary function of physical protection and minimizing water loss from the body. These structures are either derived from the dermis (bony fish scales) or are thick layers of keratinized epidermis (reptile scales) that create a tough, impermeable barrier.
Amphibians, by contrast, evolved for a life that transitions between aquatic and terrestrial environments, leading to skin adapted for moisture. Their skin is smooth, moist, and comparatively thin, which is a structural necessity for their unique method of gas exchange. The absence of scales is a defining trait of the entire class Amphibia, including frogs, toads, and all salamanders.
The Specialized Structure of Axolotl Skin
Instead of scales, the axolotl possesses a delicate integumentary system composed of a thin epidermis and a collagen-rich dermis. The outermost layer of the epidermis is non-keratinized, meaning it does not contain the tough, water-resistant protein found in the skin of land-dwelling animals. This lack of keratinization maintains the skin’s flexibility and permeability, a necessity for its aquatic existence.
A distinctive feature of axolotl skin is its abundance of mucous glands, which are concentrated in the epidermis. These glands continuously secrete a layer of mucus that forms a “slime coat” over the entire body surface. The mucus layer is composed of water, proteins, and carbohydrates, and it serves as a protective shield. This slick coating helps to prevent parasitic and bacterial infections in the aquatic environment.
The dermis, located beneath the epidermis, is rich in collagen fibers that provide structural integrity to the soft skin. This layer contains a dense network of blood capillaries close to the surface, which supports the skin’s respiratory role.
Functions of Axolotl Skin in Survival
The thin, permeable nature of axolotl skin allows it to perform a crucial function known as cutaneous respiration, or breathing through the skin. Oxygen dissolved in the water passes directly into the rich network of capillaries just below the epidermal surface, while carbon dioxide is released in the opposite direction. This gas exchange supplements the oxygen taken in by the external gills and the rudimentary lungs.
The skin’s high permeability also means it is deeply involved in osmoregulation, the process of maintaining the balance of water and salts in the body. As freshwater amphibians, axolotls are constantly absorbing excess water through their skin. They must actively expel this water through their kidneys to prevent cellular swelling.
This highly permeable design, while enabling aquatic respiration, creates a trade-off by making the animal vulnerable to environmental changes. Toxins or pollutants present in the water can be absorbed directly through the skin, presenting a significant threat to the axolotl’s survival. The delicate mucous coat provides the only minor barrier against harsh water conditions.