The black tetra (Gymnocorymbus ternetzi) also known as the black skirt tetra, petticoat tetra, high-fin black skirt tetra, and black widow tetra, blackamoor, is a freshwater fish of the characin family (Characidae). It is native to the Paraguay and Guaporé River basins of southern Brazil, Argentina, and Bolivia. The black widow tetra feeds on small crustaceans, insects, and worms.