Xenomystus nigri
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[edit] Physiology
Xenomystus nigri, the African Brown Knife Fish, is native to Liberia and the Nile basin. The design of these fish is unusual, with the body dorsolaterally flattened and elongate, giving the appearance of a knife blade. The caudal and ventral fins are fused and run from beneath the gills 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 pelvic 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/ventral 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 posesses 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.
This fish, like many of its relatives, is believed to take advantage of electrical currents to locate prey.
[edit] References
Innes, William T. Exotic aquarium fishes. T.H.F. Publishing Co, 1979
