Xenomystus Nigri - Anatomy and Appearance

Anatomy and Appearance

This fish reaches 30 centimetres (12 in) SL in length. The body of these fish is unusual, with the body ventrolaterally flattened and elongated, giving the appearance of a knife blade. The caudal and anal fins are fused and run from beneath the gill opening to the pointed end of the body, creating a uniform, skirtlike fin. This appendage gives the animal superior control in the water, as it is able to propel itself forward and backward with a minimum of wasted energy. The pelvic fins are extremely reduced and are not used in locomotion. The dorsal fin is absent. The pectoral fins of the African brown knife fish are lengthy and designed to give the animal precise control as it swims. They are often employed in a windmilling motion, in conjunction with the caudal/anal fin, as the fish retreats into its lair.

The scales of the knife fish are extremely small, giving the fish a smooth appearance broken only by its fairly prominent lateral line. Apart from its eyes, the lateral line is the knife fish's most important sensory apparatus. The African brown knife fish is nocturnal and uses the nerve-filled pits running down its body to navigate lightless waters. In addition, the eyes of this fish are large in relation to its body size. They provide the animal with excellent night vision.

The mouth is large, and the fish also possesses a pair of short barbels used in hunting. The knife fish, when not hiding away, spends much of its time swimming with its head down and the barbels in close proximity with the substrate. Combined with its acute eyes, the barbels aid the fish in locating its food.