Flagtail Prochilodus

The Flagtail Prochilodus (Semaprochilodus taeniurus) is a schooling freshwater fish in the family Prochilodontidae, native to the Amazon and Orinoco river basins of South America. It gets its common name from its boldly banded tail fin, striped in red-orange and black, which resembles a small flag. The species is a specialized detritivore-algae grazer, using a highly protrusible, sucker-like mouth to feed on biofilm and organic material coating submerged surfaces and riverbed sediment. Flagtail Prochilodus are known for undertaking large seasonal migrations in massive schools tied to river flood cycles, making them ecologically important within South American river food webs.

Flagtail Prochilodus are identified chiefly by their silvery, deep body and vividly banded tail.

• Body: laterally compressed, deep-bodied, silvery overall with a slightly humped back
• Tail: distinctive, boldly striped in alternating black and red-orange bands, the clearest field mark
• Mouth: small, downturned, highly protrusible, adapted for grazing surfaces
• Fins: dark dorsal fin, otherwise mostly translucent to silvery fins aside from the banded tail
• Size: typically 25-35 cm The striped tail readily separates it from other silvery characin-like fish sharing its range, most of which lack such bold caudal fin banding.

Flagtail Prochilodus are native to the Amazon and Orinoco river basins across Brazil, Peru, Colombia, and Venezuela, inhabiting main river channels, floodplain lakes, and tributary streams. They favor warm, slow-to-moderate flowing water and are strongly tied to the seasonal flood pulse of their river systems, moving between main channels and flooded forest habitat as water levels rise and fall. The species tends to school over open sandy or muddy substrates and around submerged wood, where biofilm and algae accumulate. Their range covers a broad swath of lowland tropical South America within these two major watersheds.

Flagtail Prochilodus are highly social, forming large, dense schools that undertake extensive seasonal migrations along river channels timed to flood and dry-season cycles. They feed by grazing algae, biofilm, and organic detritus from submerged surfaces and sediment using a specialized protrusible mouth capable of forming a temporary sucking disc. These mass migrations, sometimes involving vast numbers of fish, play an important ecological role in nutrient cycling and serve as a major food source for predatory fish, birds, and other wildlife along the migration route. Spawning is closely tied to rising water levels at the start of the flood season.