This is the rarest knife fish species. It is also the most beautiful and largest growing, reaching up to 36 inches. It is all black with metallic blue shine in the scales.

Its anal fin and caudal fin (tail fin) are joined, giving it a long continuous fin along the underside. This fin undulates, allowing it to move either forwards or back wards, making it a very graceful swimmer.

They are generally peaceful and will do well with other fish that are not particularly aggressive and that are too large to fit into its mouth.