Semaprochilodus is a genus of flagtail prochilodus, large schooling characiforms of the Amazon and Orinoco basins named for the bold, banded pattern on their caudal fin. Atlas species reach 11–21.5 in and share the family's distinctive protrusible, sucker-like mouth, angled downward and built to scrape algae, biofilm, and organic detritus from submerged wood, rocks, and sediment rather than to seize prey. In the atlas the genus spans Brazil, Colombia, Venezuela, Ecuador, French Guiana, Guyana, Peru, and Suriname, tracking the major river systems that drain the Amazon and Orinoco.
Several Semaprochilodus species, known locally as jaraqui, undertake large seasonal shoaling migrations and support significant subsistence and commercial fisheries across their range - Semaprochilodus brama and Semaprochilodus insignis in particular are well known food fish in the Amazon basin. In the aquarium trade the group turns up under names like flagtail prochilodus, kept less for color than for their active shoaling behavior and usefulness as algae grazers in very large tanks, though their adult size puts them well beyond typical community setups. Conservation-wise the genus looks secure as assessed: all six atlas species carry a Least Concern IUCN status.