Cynodontidae, from Ancient Greek κύων (kúōn), meaning "dog", and ὀδούς (odoús), meaning "tooth", 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 three genera and 8 species. The largest species in this family ranges up to 117 cm (3.84 ft).

They are characterized by an oblique mouth and very long distinct canines, which are used to capture and stab their prey, other fish that can be up to half the length of the cynodontine itself. They are not prized as food fish, but are important in subsistence and commercial fisheries. Hydrolycus are game fish, having been recently added to the International Game Fish Association in the fly and rod class. Cynodontid fish are also sometimes housed in aquaria.

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