What is "knifefish"

Knifefish may refer to several knife-shaped fishes:

• The Neotropical or weakly electric knifefishes, order Gymnotiformes, containing five families:
  • Family Gymnotidae (banded knifefishes and the electric eel)
  • Family Rhamphichthyidae (sand knifefishes)
  • Family Hypopomidae (bluntnose knifefishes)
  • Family Sternopygidae (glass and rat-tail knifefishes)
  • Family Apteronotidae (ghost knifefishes)
• The featherbacks, family Notopteridae.
• The aba, Gymnarchus niloticus
• Four other unrelated fish species not in any of the above families:
  • Grey knifefish, Bathystethus cultratus.
  • Blue knifefish, Labracoglossa nitida.
  • Collared knifefish or finscale razorfish, Cymolutes torquatus.
  • Jack-knifefish, Equetus lanceolatus.

The Knifefish is an autonomous unmanned underwater vehicle (UUV) under development by General Dynamics Mission Systems and Bluefin Robotics for the United States Navy. It is a propeller-driven minesweeping robot designed to replace the Navy's trained dolphins and sea lions after the retirement of the 50-year-old Marine Mammal Program in 2017. The Knifefish was first unveiled at a Navy exposition in April 2012, and is intended to operate in concert with the Navy's littoral combat ships (LCS) as part of a specialised counter-mine system. The Navy plans to begin sea trials of the Knifefish in 2015, and to enter it into active service in 2017.