When first discovered in the 1930s, these eyeless, pigmentless fish were assigned their own genus, Anoptichthys. Since then, ichthyologists have determined they are at least 30 genetically isolated populations of the Mexican tetra, which is normally a silvery fish with well-developed eyes that is found north to the Rio Grande Valley in Texas. Fish collected in one cave, la Cueva Chica, in San Luis Potosi in the 1940s, are the ancestors of the fishes made available by commercial breeders to home aquarists, public aquariums and zoos.