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.
This popular aquarium fish was unknown to science until 1956, when ichthyologists at the Smithsonian Institution and Stanford University published descriptions a day apart. It took a meeting of the International Commission on Zoological Nomenclature to determine the Smithsonian had published first. Found only in the Rio Negro and Orinoco Rivers, they are provided both through ecologically sustainable collecting in Brazil and fish farms in Asia and Europe.
It appears there are no documented cases of piranhas killing people, but there have been several cases where they have eaten humans that had drowned. In general, these specialized relatives of the tetras are opportunistic scavengers. Of the 50 or so species found in South American Rivers, this one is the most familiar, and is popular in aquariums for its bright colors. If maintained in groups of less than four, piranhas are likely to eventually kill each other. They have been bred many times in captivity.
Growing to a foot in length, this eye-catching relative of tetras and piranhas is a typical inhabitant on flooded forests in South America. For more than 50 years it has been very popular in the pet trade. While having a reputation for harassing other fishes in home aquariums, it is not aggressive in roomy accommodations.