Cynodontidae
Cynodontidae, also known as dogtooth characins or vampire tetras, are a family of predatory, characiform freshwater fishes from South America. This group is not very diverse, and includes only five genera and 14 species. Most of what is known about this family is from the members of the subfamily Cynodontinae, which includes the largest species of this family, up to . The members of subfamily Roestinae only reach up to . and are less known. Physical characteristics. Cynodontidae are elongated in shape with a silvery or grey colour and an upturned mouth. Some species have a hunchbacked appearance. The family names  (both scientific and common) derive from the long and well-developed canines which are used to spear their prey, mainly other fish. Their pectoral fins are also expanded. The maximum length reached is . Distribution and habitat. These fish live in midlevel to surface waters of rivers, lakes, and flooded forests. Most species of this family originate from the Orinoco and Amazon basins, as well as rivers of the Guianas. One species, "Rhaphiodon vulpinus", ranges as far south as the Paraná-Paraguay and Uruguay basins, and "Gilbertolus" is found in the Atrato, Magdalena and Maracaibo basins. Fossil species are also known  from Argentina. Relationship to humans. "Hydrolycus" species are game fish, having been recently added to the International Game Fish Association in the fly and rod class. Cynodontid fish are also sometimes kept in aquaria.