Thayeria

The false penguin tetra, Thayeria boehlkei, is a characin probably restricted to the upper Amazon in Peru and the Rio Araguaia in Brazil. By far the most popular Thayeria in the hobby, it is usually sold as the penguin tetra, a name first given to T. obliqua. Its thick black stripe runs from the lower caudal lobe along the body to the opercle. A schooling species, it should be kept in a group of at least six.

The half-striped penguin tetra, Thayeria ifati, is a characin that appears to be endemic to the rivers Maroni and Approuague in French Guiana. Of the three Thayeria, T. ifati is the least often seen in the hobby. In this species the black stripe is confined to the upper part of the lower caudal lobe, and the dorsal and anal fins develop red tips in good condition. Like its congeners, it swims in an oblique, head-up style.

The penguin tetra, Thayeria obliqua, is a characin from the central Amazon and Rio Tocantins basins and the Rio Guaporé in Brazil. The type species of the genus, it was the original penguin tetra, though T. boehlkei is now usually sold under that name. In T. obliqua the black caudal stripe tapers upwards and fades before reaching the dorsal fin. It should be kept in a group of at least six.