The Clown Knifefish has a unique “knife blade” body shape and ability to swim backwards using their undulating bottom fin make them fascinating additions to your aquarium. It is a very popular knifefish. This is partly because of its common availability and being relatively inexpensive. But its also a favorite because it is extremely attractive. They usually have a pattern of large spots, but this can be quite variable and it seems that no two Clown Knifefish are exactly alike.The normal coloring of the Clown Knifefish is a silvery gray characterized by a variable pattern of large spots above the base of the anal fin. Yet sometimes they may have no spots at all, and sometimes they may have two rows of smaller spots. Other common names it is known by are Clown Featherback Fish, Spotted Knifefish, Spotted Featherback Fish, and Clown Knife. The Clown Knife has the typical knifefish body shape, flat and elongated with an arched back. 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.