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.