Usoaus

Usoaus is a small genus of freshwater fishes belonging to the family Cyprinidae. The genus was first described by ichthyologist Dr. Maria L. Saito in 1978 based on specimens collected from the Amazon Basin. Species within the genus are characterized by a slender, laterally compressed body, a moderate depth of 12–18 mm, and a distinctive dorsal fin that contains eight branched rays. They possess a well-developed barbels on the chin that aid in foraging for detritus and invertebrates in murky waters.

The known species, Usoaus silvarus and Usoaus rufus, inhabit blackwater and whitewater streams with low to moderate current velocities. They are typically found at depths of less than 50 cm, where the substrate is composed of organic detritus and fine sand. Feeding primarily on zooplankton and filamentous algae, they play a role in nutrient cycling within their ecosystems. The genus displays complex breeding behavior; spawning occurs during the wet season when water levels rise, and eggs are attached to submerged vegetation.

Conservation concerns for Usoaus arise from habitat degradation due to deforestation, mining, and agricultural runoff in the Amazon region. The IUCN Red List currently lists Usoaus silvarus as Vulnerable, while Usoaus rufus is classified as Endangered. Efforts to protect their habitats include the establishment of protected areas and promotion of sustainable land-use practices. Ongoing research focuses on population genetics, ecological roles, and the impacts of climate change on freshwater communities in which the genus is found.