This species is rare in the aquarium trade but is arguably more suitable for the home aquarium than some of its better-known relatives given its adult size and relatively docile behaviour.

Other vernacular names include ‘Dientón’ (Peru), ‘Perrito’ (Ecuador), ‘Payara-chata’ or ‘Payarin’ (Venezuela) and ‘Icanga’, ‘Minguilista’ or ‘Peice-cachorro’ (Brazil), some of which are also applied to related species.

Vernacular names in Brazil include ‘Cachorra’ or ‘Pirandirá’, although these are also applied to congeners.

It can be told apart from all congeners by the following combination of characters: head and body silvery with dark dorsal surface; an elongate dark blotch posterior to the opercle; dorsal, caudal and anal-fin rays reddish to orange proximally with some individual variation in intensity and tonality; adipose fin dark, with diffuse black pigmentation.

H. armatus should probably not be considered a home aquarium subject at all given its eventual size and migratory natural behaviour.

Unfortunately, juveniles are seen for sale quite regularly, most often without adequate information regarding their long-term care, and it’s common to see them being maintained in medium-sized aquaria with no possibility of achieving their potential.

This species may be referred to using a variety of names including ‘scomb’, ‘sabre tooth tetra’, ‘sabre tusk barracuda’, ‘dog tooth characin, ‘vampire fish’, ‘Cachorra’ or Pirandirá (the latter two names being used in Brazil where they’re also applied to congeners).

It’s regularly confused with the payara, H. armatus, though that species grows considerably larger, is pop…

R. vulpinus is the most widely-distributed member of the family Cynodontidae.

Type locality is given simply as ‘Brazilian rivers’, but this species is currently understood to be distributed in the Amazon basin from the Río Ucayali system in Peru, eastward as far as the rio Xingu in Brazil, plus the rio Tocantins and Rio Capim basins.

It’s also known from the Río Orinoco ba…