Look up: knifefish

1. knifefish
   any of certain New World fishes of the suborder Gymnotoidei, order Cypriniformes. Knifefishes comprise, at most, about 50 species of Central and ... [3 related articles]
   Found on http://www.britannica.com/eb/a-z/k/40
   
   
2. knifefish
   Any of a group of fishes in which the body is deep at the front and drawn to a narrow or pointed tail at the rear, the main fin being the well-developed long ventral (stomach) fin that completes the knifelike shape. The ventral fin is rippled for forward or backward movement. Knifefishes produce electrical fields, which they use for navigation....
   Found on http://www.talktalk.co.uk/reference/ency