Hydrolycus is a genus of large dogtooth characins from tropical South America, where found in the Amazon and Orinoco basins, as well as rivers of the Guianas.

[1] The genus includes the largest dogtooth characins, reaching up to 1.17 m (3.8 ft) in length.

[1] They have long, pointed teeth (shorter and less extreme in H. wallacei) used for spearing their prey, generally smaller fish.

[2] In a study of the stomachs of 45 individuals, most were empty, but among the remaining the prey fish were 15–50% of the length Hydrolycus itself.

[3] In 1999 two new species were described, the first in this genus in 158 years.