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The axolotl () also known as a Mexican salamander (''Ambystoma mexicanum'') or a Mexican walking fish, is a neotenic salamander, closely related to the tiger salamander.〔http://www.aquariumindustries.com.au/wp-content/uploads/2012/07/Mexican-Walking-Fish.pdf〕〔(【引用サイトリンク】title=Axolotols (Walking Fish) )〕 Although the axolotl is colloquially known as a "walking fish", it is not a fish, but an amphibian. The species originates from numerous lakes, such as Lake Xochimilco underlying Mexico City.〔(【引用サイトリンク】title= Ambystoma mexicanum )〕 Axolotls are unusual among amphibians in that they reach adulthood without undergoing metamorphosis. Instead of developing lungs and taking to land, the adults remain aquatic and gilled. Axolotls should not be confused with waterdogs, the larval stage of the closely related tiger salamanders (''A. tigrinum'' and ''A. mavortium''), which are widespread in much of North America and occasionally become neotenic. Neither should they be confused with mudpuppies (''Necturus'' spp.), fully aquatic salamanders which are not closely related to the axolotl but bear a superficial resemblance. , wild axolotls were near extinction due to urbanization in Mexico City and consequent water pollution. They are currently listed by CITES as an endangered species and by IUCN as critically endangered in the wild, with a decreasing population. Axolotls are used extensively in scientific research due to their ability to regenerate limbs. Axolotls were also sold as food in Mexican markets and were a staple in the Aztec diet. A four-month-long search in 2013 turned up no surviving individuals in the wild. Previous surveys in 1998, 2003 and 2008 had found 6000, 1000 and 100 axolotls per square kilometer in its Lake Xochimilco habitat, respectively. ==Description== A sexually mature adult axolotl, at age 18–24 months, ranges in length from , although a size close to is most common and greater than is rare. Axolotls possess features typical of salamander larvae, including external gills and a caudal fin extending from behind the head to the vent. Their heads are wide, and their eyes are lidless. Their limbs are underdeveloped and possess long, thin digits. Males are identified by their swollen cloacae lined with papillae, while females are noticeable for their wider bodies full of eggs. Three pairs of external gill stalks (rami) originate behind their heads and are used to move oxygenated water. The external gill rami are lined with filaments (fimbriae) to increase surface area for gas exchange. Four gill slits lined with gill rakers are hidden underneath the external gills. Axolotls have barely visible vestigial teeth, which would have developed during metamorphosis. The primary method of feeding is by suction, during which their rakers interlock to close the gill slits. External gills are used for respiration, although buccal pumping (gulping air from the surface) may also be used to provide oxygen to their lungs. Axolotls have four pigmentation genes which when mutated create different colour variants. The normal wild type animal is brown/tan with gold speckles and an olive undertone. The four mutant colors are leucistic (pale pink with black eyes), albino (golden with gold eyes), axanthic (grey with black eyes) and melanoid (all black with no gold speckling or olive tone). In addition there is wide individual variability in the size, frequency, and intensity of the gold speckling and at least one variant that develops a black and white piebald appearance on reaching maturity. Because pet breeders frequently cross the variant colours, animals that are double recessive mutants are common in the pet trade, especially white/pink animals with pink eyes that are double homozygous mutants for both the albino and leucistic trait.〔Frost et al, (A color atlas of pigment genes in the Mexican axolotl (Ambystoma mexicanum) ) Differentiation Volume 26, Issue 1-3, pages 182–188, June 1984〕 Axolotls also have some limited ability to alter their colour to provide better camouflage by changing the relative size and thickness of their melanophores.〔Pietsch & Schneider (Vision and the skin camouflage reactions of Ambystoma larvae: the effects of eye transplants and brain lesions ) Brain Research Volume 340, Issue 1, 5 August 1985, Pages 37–60〕 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Axolotl」の詳細全文を読む スポンサード リンク
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