Knifefish

This knifefish lives in one river system only: the Rio Tocantins in Brazil, and it is found nowhere else. It is one of the glass knifefishes, a South American group built along quite different lines from an ordinary fish. It grows to about 43.5 cm.

Glass knifefishes all share the blade-shaped body and the missing tail fin, so the outline will not tell them apart. Look along the base of the long belly fin: on this species a broad dusky to dark band runs there, where the fin meets the body. Take that together with the thin dark flank line, and the pair of marks separates it from its relatives.

The body is long and squeezed flat from side to side, like a blade, and it is covered in scales from end to end. There is no tail fin. Instead the body tapers back into a thin filament. One very long fin runs along the underside for most of the body. A narrow dark line follows the lateral line, the faint sensory stripe along the flank.