Mexican Blind Cave Fish Astyanax mexicanus

There are many species of blind or partially blind cave-dwelling fish in many countries. These have adapted to a dark, cave environment where sight is of little or no importance and other senses compensate. The Mexican Blind Cave Fish has a totally normal surface-dwelling (stream/river) variant of exactly the same species - the Mexican Tetra. The latter has eyes, sight and a drab pigment.

The Mexican Blind Cave Fish and Mexican Tetra are native to Texas, especially the Rio Grande, and eastern Mexico. The former lives in underground caves and, because it does not need its eyes, flaps of skin have grown over them for protection. The body is a pinkish white with no pigment but it has a lateral line that is sensitive to changes in water movement and pressure. (The sighted, surface stream-dwelling relative also shows a lateral line on silver-grey.) They grow to 12cm long.

Like other Tetra, they are schooling species. Although it is occasionally called the Blind Tetra, that name is more commonly given to the Brazilian Blind Tetra, Stygichthys typhlops, native to caves in northern Brazil. Some recognise the blind, cave-dwelling form as a separate species from the sighted, pigmented Mexican Tetra, giving it the name A. jordani.