TAXONOMY
Kingdom: Animalia
Phylum: Chordata
Class: Actinopterygii (ray-finned fishes)
Order: Characiformes (Characins)
Family: Characidae (Characins)
Genus/species: Astyanax mexicanus
GENERAL CHARACTERISTICS: The head is notable for the absence of eyes. Young are born with functioning eyes which become completely enclosed in tissue as fish grows. The lack of sight is compensated by a highly developed lateral line that detects vibrations and changes in the water. The fish is without pigmentation and is plain pink with a silver sheen. They live in schools and grow to about 12 cm or 4.72 inches.
DISTRIBUTION/HABITAT: Texas, New Mexico, and eastern and central Mexico in freshwater pools within dark caves.
DIET IN THE WILD: A keen sense of smell and electrolocation aid in finding food. Blind cave fish are omnivores and feed on animal and plant remains that wash into the caves and on bat droppings from cave ceilings. Much of their time is spent searching for food; they are able to store four times more energy as fat than their surface-dwelling relatives, allowing them to deal with irregular food supplies.
REMARKS: Two forms of A. mexicanus (eyed and eyeless) being members of the same species, are closely related and can interbreed.
The loss of eye tissue in the blind cavefish, which occurs within a few days of their development, happens through epigenetic silencing of eye-related genes, according to a study led by the National Institutes of Health. Epigenetic regulation is a process where genes are turned off or on, typically in a reversible or temporary manner. This mechanism differs from genetic mutations, which are permanent changes in the DNA code. The study appears in Nature Ecology & Evolution.
References
California Academy of Sciences Steinhart Aquarium Water planet Senses Cluster, Dr Bart Sheperd
Ron’s flickr http://www.flickr.com/photos/cas_docents/sets/72157608608528651/with/2999116145/
Ron’s WordPress Shortlink http://wp.me/p1DZ4b-11I
Read more at: phys.org/news/2018-05-eye-loss-cavefish.html#jCp