Semaprochilodus insignis, also known as the Flagtail Prochilodus, is a species of freshwater fish native to South America, specifically the Amazon and Orinoco basins. It belongs to the family Prochilodontidae and is a popular species among fishkeepers for its interesting appearance and peaceful nature.

The Flagtail Prochilodus has a silver body with a black and white striped pattern on its caudal fin, which gives it its common name. It can grow up to 30 cm (12 in) in length, but in captivity, it usually reaches around 15 cm (6 in). It is a hardy species that can adapt to a range of water conditions, but it prefers a pH of 6.0-7.5 and a temperature range of 24-28°C (75-82°F).

In the wild, Flagtail Prochilodus are primarily herbivorous, feeding on algae and plant matter. In captivity, they will accept a variety of prepared foods, including pellets, flakes, and frozen foods. They are a peaceful species that can be kept in groups of six or more individuals in a suitably-sized aquarium. However, due to their large adult size, they require a spacious aquarium with plenty of swimming room and hiding places. They are a good addition to a community tank, as they are not aggressive towards other fish.