Astyanax mexicanus

The Mexican Cave Tetra (Astyanax mexicanus) is a small fish that is reasonably popular among aquarists, particularly the variant that, in its wild state, lives in deep caves and has lost the power of sight and even its eyes. The fish can still find its way around by means of its centreline, which is highly sensitive to fluctuating water pressure. Apart from the unusual feature of its blindness, it is not considered an attractive fish - it is devoid of distinctive colouring and therefore appears as uniformly pale pink.

The two varieties (with and without eyes) are still closely related and can interbreed. They are grouped with other tetras in the characin family, Characidae.