Payaras are called vampire fish because, in addition to spiky teeth, they have two elongated fangs jutting up from their lower, upturned jaws.
https://www.youtube.com/watch?v=WjguZEu86s0
Payaras hunt alone by swimming into schools of fish and use their fangs to impale prey which includes piranhas. Fish that eat piranhas are scary animals indeed.
https://en.wikipedia.org/wiki/Payara
The payara, which is also sold as the saber tooth barracuda, vampire fish, vampire tetra, or saber tusk barracuda, is a popular species for large, aggressive aquariums. It requires a large aquarium and can only be mixed with relatively large species, as smaller will be seen as potential prey.