Facts About Mexican Walking Fish
The axolotl, also known as a Mexican salamander or a Mexican Walking Fish, is a neotenic salamander, closely related to the tiger salamander. 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 and these Mexican Walking Fish 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.
A sexually mature adult axolotl (Mexican Walking Fish), at age 18–24 months, ranges in length from 15–45 cm, although a size close to 23 cm (9 in) is most common and greater than 30 cm (12 in) 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 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 (Mexican Walking Fish) 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 different colours, including two mutant colors. The two normal colors are ‘wildtype’ (varying shades of brown usually with spots) and melanoid (black). The two mutant colors are leucistic (pale pink with black eyes) and albino (golden, tan or pale pink with pink eyes).
As of 2010, wild axolotls (Mexican Walking Fish) 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.