The axolotl, a fascinating amphibian, is known for its diverse appearances. These aquatic salamanders display a surprising array of colors. This wide spectrum of coloration is influenced by both natural genetic variations and selective breeding efforts in captivity.
Understanding Natural Coloration
In their native habitat, the wild type axolotl exhibits a mottled brownish-grey or olive-green coloration, often with gold speckles. This natural pigmentation provides effective camouflage in the murky waters of their original Mexican lake environment.
Beyond the wild type, two other common color variations occur naturally: Leucistic and Albino axolotls. Leucistic axolotls have a pale pink or white body with black or dark blue eyes and often bright red or pink gills. These individuals may also show some dark speckling, particularly on the face or spine. Albino axolotls, in contrast, are characterized by a creamy white or pale pink body with red or clear eyes, and vibrant pink or red gills. This lack of dark pigment makes their blood vessels visible, giving their gills and eyes a striking hue.
Common Domesticated Color Morphs
Selective breeding in captivity has led to the development of numerous distinct color morphs. Melanoid axolotls are solid black or very dark grey, lacking the shiny iridophores found in wild types. Their eyes are dark without the golden ring seen in wild types, and their gills are often a subdued dark purple. This morph can sometimes darken significantly with age.
Golden albino axolotls have a luminous golden-yellow to light tan body, often with shiny speckles across their skin. They possess red or clear eyes and have golden or pinkish gills. Their coloration can range from almost pure white at birth, gradually deepening to a rich gold as they mature. Copper axolotls display a muted brown to coppery or light brownish-orange body, often with light or dark spots and sometimes iridophores. This morph is a type of albinism, resulting in red-tinted eyes and the absence of black pigments.
Unique and Rare Color Variations
Beyond the more common morphs, some axolotls exhibit unique and rare color variations, often due to specific genetic mutations or laboratory introductions. Green Fluorescent Protein (GFP) axolotls were created in a laboratory setting by inserting a fluorescent protein gene into their genome. These axolotls glow a vibrant green under a blacklight, and some may even have a greenish tint under normal lighting conditions.
Axanthic axolotls lack yellow pigments (xanthophores) and reflective cells (iridophores). This results in a greyish, brownish, or even purplish coloration, often appearing as a “washed-out” wild type. Chimera or Mosaic axolotls are rare, displaying two distinct color patterns on different parts of their body. This unusual appearance occurs when two eggs fuse during embryonic development, leading to an individual with two separate genetic makeups.
The Genetics Behind Axolotl Colors
Axolotl coloration is determined by specialized pigment cells called chromatophores. There are three primary types of these cells: melanophores, xanthophores, and iridophores. Melanophores produce black and brown pigments, known as eumelanin. Xanthophores are responsible for yellow, orange, and reddish hues, containing pigments like carotenoids and pteridines.
Iridophores contain crystallized purines, which create reflective, shiny, or iridescent effects, often appearing gold or silver. The presence, absence, or distribution of these pigment cells, controlled by specific genes, dictates an axolotl’s overall color. For example, albinism results from the inability to produce melanin, while melanism involves an increased number of melanophores and a lack of iridophores.