The axolotl (Ambystoma mexicanum) is a salamander popular in the exotic pet trade. Unlike most amphibians, it exhibits neoteny, retaining its fully aquatic, juvenile form, external gills, and finned tail throughout its life. While wild axolotls are typically mottled brown or gray, captive breeding has produced many color variations. This article identifies the genetic variation responsible for the familiar pink appearance.
The Identity of the Pink Axolotl
The common pink or pale-white axolotl is known as the Leucistic color morph, often nicknamed a “Lucy.” This coloration results from a genetic mutation affecting pigment cell distribution. A defining feature of the Leucistic axolotl is its dark eye color, typically black or dark blue, which contrasts sharply with its light body. This morph may also develop tiny, dark freckles, particularly around the head and back.
Understanding Leucism
Leucism is a genetic condition characterized by a partial loss of pigmentation. In axolotls, this occurs because melanophores (dark pigment cells) fail to properly migrate to the skin during embryonic development. The Leucistic morph’s light body therefore lacks these dark color cells. The pink hue seen in the skin and the distinctive frilly external gills is due to the visibility of the animal’s blood circulating beneath the translucent surface.
The leucistic trait is caused by a recessive gene that prevents the full development of dark pigmentation. This results in the salamander’s pale appearance, which ranges from nearly pure white to a soft, rosy pink. The pink shade intensifies when the animal is active or when blood flow increases through the highly vascularized external gills.
Leucistic Versus Albino
The Leucistic morph is frequently confused with the Albino axolotl because both appear pale, but they represent two distinct genetic conditions. Albinism is the complete absence of melanin (dark pigment) throughout the entire body, including the eyes. An Albino axolotl will always have red or pink eyes because the lack of melanin allows the blood vessels in the retina to show through.
The presence of dark eyes in the Leucistic axolotl confirms that pigment-producing cells are still present, even if they have not fully migrated to the body surface. This retention of pigment is the most reliable way to visually distinguish a Leucistic axolotl from an Albino. Furthermore, Leucistic individuals may still possess other pigment cells, which is why some develop small dark freckles.