Bony fish · Characiformes · Characidae

Mexican Tetra

Astyanax mexicanus

Not Evaluated

It has not yet been assessed against the IUCN criteria. See full glossary

The Mexican tetra is a small characin that exists in two forms of the same species: a surface form, silvery and with normal eyes, and a form living in caves in north-eastern Mexico, without eyes and without pigment. The cave populations were isolated in separate caves and lost their sight independently in each one.

Size

8 cm – 12 cm

Diet

Omnivore

Combines animal and plant food depending on availability.

Sighting difficulty

Unknown

FreshwaterOmnivore Fish Freshwater

3countries 3parks4same family

Fun facts

adaptaciónIt is born with eyes that stop developing and end up covered by skin, since in the total darkness of the caves they confer no advantage.
GeneralThe same species has sighted populations in the rivers and blind ones in the caves.
Cave and surface individuals can interbreed and produce fertile offspring: they are the same species, separated by a few hundred thousand years.
The blind form makes up for the lack of sight with more taste buds over its body and a hypersensitive lateral line that lets it map the cave from pressure waves.
They sleep far less than their surface relatives and tolerate very long fasts.
It has two forms within the same species: a surface one with eyes and pigment and a cave one, blind and unpigmented; the two remain fully interfertile.
Some 35 cave populations are known with no eyes or greatly reduced ones, and the loss of sight has happened independently several times.
A study at Lund University calculated that keeping its sight costs a juvenile 15 % more energy, which would explain the advantage of losing it where there is no light and food is scarce.
The cave form has taste buds on the outside of its lower jaw and barely sleeps.