Sternopygus is a genus of glass knifefishes found in tropical and subtropical South America (south to the Río de la Plata Basin), and Panama. It is the only extant member of the subfamily Sternopyginae, with the related fossil genus Humboldtichthys also known from Bolivia.
They inhabit a wide range of freshwater habitats, from fast-flowing rivers to essentially static waters in floodplains, and shallow habitats to the bottom of deep rivers. S. macrurus will even visit brackish mangroves to feed.
They are medium to large knifefish, with a maximum total length of depending on the exact species. They feed on invertebrates, small fish and fruits. Most members of Gymnotiformes are nocturnal, but Sternopygus are both nocturnal and diurnal.
Species There are currently twelve recognized species in this genus.
Sternopygus aequilabiatus (Humboldt, 1805) Sternopygus arenatus (Eydoux & Souleyet, 1850) Sternopygus astrabes Mago-Leccia, 1994 Sternopygus branco Crampton, Hulen & Albert, 2004 Sternopygus dariensis Meek & Hildebrand 1916 Sternopygus embera Torgersen, Galindo-Cuervo, Ortega-Lara, Lujan, Reis & Albert, 2026 Sternopygus macrurus (Bloch & Schneider, 1801) (Longtail knifefish) Sternopygus obtusirostris Steindachner, 1881 Sternopygus pejeraton Schultz, 1949 Sternopygus sabaji Torgersen & Albert, 2022 Sternopygus sarae Torgersen, Galindo-Cuervo, Reis & Albert, 2023 Sternopygus xingu Albert & Fink, 1996
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