Metynnis

Metynnis argenteus is a silver dollar, a relative of the piranhas probably endemic to the Rio Tapajós drainage in Brazil. It is very similar to M. hypsauchen, and both are sold in the hobby as 'silver dollar'. The two are virtually identical in appearance and care, but M. hypsauchen has a black blotch above and behind each eye. An avid plant-eater, it is best kept in a group of at least five and may eat much smaller fish.

The silver dollar, Metynnis hypsauchen, is a relative of the piranhas with a patchy distribution in Guyana, Brazil, Peru and Bolivia. Sometimes called the plain metynnis, it is sold under the same name as the very similar M. argenteus and differs in the black blotch above and behind each eye. A striped form is not a distinct species. An avid plant-eater, it is best kept in a group of at least five.

Metynnis lippincottianus is a spotted silver dollar from Brazil and French Guiana, found in the lower and middle Amazon and the Oyapock system. It is occasionally seen for sale, sometimes as 'silver dollar', and its spotted pattern tells it apart from M. argenteus and M. hypsauchen. The spots are less pronounced than in M. maculatus, with which it shares a common name. The precise extent of its range is unclear.

The spotted metynnis, Metynnis maculatus, is a silver dollar probably confined to the upper rio Madeira and upper rio Paraguai in Bolivia and Brazil. It is most often confused with M. argenteus and M. lippincottianus, but it has more midlateral scales and more spines on the ventral keel than either. It schools in nature and needs a very large tank with a group of six or more.