Tenebrosternarchus is a monospecific genus of weakly electric knifefish in the family Apteronotidae. The only species in the genus is Tenebrosternarchus preto. It is native to large river channels and major side branches in the Amazon Basin, and is common in the Tefé River and the Rio Solimões to a depth of 14 m (46 ft). It is found in both whitewater and blackwater habitats. The species name preto comes from the Portuguese word for "black", referring to its coloration. Prior to 2020, it was placed in the genus Sternarchogiton.