The axolotl, a unique salamander, fascinates many with its distinctive appearance and aquatic lifestyle. These amphibians possess a flat head, a long tail, and four lizard-like limbs. They are particularly notable for retaining their larval features, such as feathery external gills and a tail fin, throughout their entire lives, a characteristic known as neoteny. This sets them apart from most other salamanders that undergo metamorphosis to live on land. Axolotls are popular pets globally, and are also significant subjects in scientific research due to their remarkable regenerative abilities.
Understanding Axolotl Classification
Despite the wide array of visible differences, the axolotl is scientifically classified as a single species, Ambystoma mexicanum. The idea of various “types” often refers to genetic color variations rather than distinct species.
This amphibian is native to the Valley of Mexico, specifically the lake complex of Xochimilco, and historically, Lake Chalco. Lake Chalco no longer exists, and Lake Xochimilco is now primarily a system of canals, leading to a drastic reduction in their natural habitat. The wild population of axolotls is critically endangered, facing threats such as habitat loss, water pollution, and the introduction of invasive fish species.
Common Axolotl Morphs
What people commonly refer to as different “types” of axolotls are actually genetic variations in coloration, known as morphs, primarily developed through selective breeding in captivity. These morphs exhibit a spectrum of appearances.
The “Wild Type” axolotl most closely resembles its natural ancestors, typically displaying a mottled brown or olive base with black, green, or gold speckles. Wild types often have dark eyes, sometimes with a golden ring around the pupil, and their gills match their body color, possibly with red or pink tips.
Leucistic axolotls are characterized by a pale white or pink body with black or dark blue eyes. Their feathery external gills are usually a vibrant red or pink due to visible blood vessels beneath their translucent skin. They may develop dark freckles, especially on the face or spine.
Albino axolotls, in contrast to leucistics, lack all dark pigment (melanin). This absence results in red or clear eyes because the blood vessels in the retina are visible. There are two main forms: White Albino, predominantly white or very pale pink, and Golden Albino, with a vibrant golden-yellow to light tan coloration. Both albino types have pink gills.
Melanoid axolotls are notably dark, ranging from solid black to very dark gray, without shiny speckles or iridescence. This is due to an excess of melanophores (dark pigment cells) and a lack of iridophores (cells that create reflective pigments). Their eyes are typically dark, lacking the shiny golden ring seen in wild types, and their gills are often dark purple or black.
Rarer variations include Chimera and Mosaic axolotls. A Mosaic axolotl displays a patchwork of colors from different morphs across its body, resulting from a genetic mutation during embryonic development. A Chimera axolotl is a rare occurrence where two embryos with different genetic makeups fuse, creating an individual that can appear split down the middle with two distinct colorations. These unique patterns are random and cannot be consistently bred.
Differences in Wild and Captive Axolotls
The visual diversity of axolotls is largely a result of human intervention. Wild axolotls primarily exhibit the “wild type” coloration, which is a dark, mottled brown or olive. This natural pigmentation offers camouflage, allowing them to blend into the muddy lakebeds and aquatic vegetation of their native habitat.
In contrast, the wide range of vibrant morphs seen in captivity, such as leucistic, albino, and melanoid, are not typically found in the wild. These diverse colorations have been developed through selective breeding by hobbyists and researchers for aesthetic purposes. While captive populations thrive and are widely distributed, they often have reduced genetic diversity due to inbreeding. This difference highlights how human preferences have shaped the visible “types” of axolotls, distinct from their natural forms.