Hydrolycus armatus

This species of fish is found in the Amazon, Orinoco, and Essequibo Basins in tropical South America.^[3][9] They are found in several different freshwater habitats, but often in fast-flowing water.^[7][10] They are typically found in deeper waters during the day.^[10] The species is locally common; in a major study of a Venezuelan floodplain river, 1⁄3 of the collected fish were H. armatus, and the species was particularly common in creeks and lagoons.^[11] At least some populations are migratory.^[10]

Hydrolycus armatus is overall silvery. In adults, the base of the tail and anal fin are pale yellowish, and the distal part is blackish, contrasting with a narrow white edge at the very tip (unique among Hydrolycus species).^[5][9][12]

A typically reported maximum total length of this fish is 89 cm (2 ft 11 in),^[3] but records show specimens up to 95 cm (3 ft 1 in) in Venezuela^[6] and more than 100 cm (3.3 ft) in Brazil.^[7] It typically weighs up to 8.5 kg (18 lb 12 oz),^[3] but can reach almost 18 kg (40 lb).^[7] It has frequently been confused with the generally smaller H. scomberoides.^[5][9] H. armatus reaches maturity when at least 30 cm (1 ft) long.^[10] Like other dogtooth characins, it has very long pointed canine teeth. In H. armatus these can surpass 10 cm (4 in) in length in large individuals.^[4] These are used for spearing their prey, usually other fish.^[12]