Knifefish are a group of freshwater fish belonging to the order Gymnotiformes. They are known for their elongated bodies and unique swimming style, which involves undulating their bodies and using a long, flat tail. Knifefish are primarily found in the rivers and lakes of South America, particularly in the Amazon Basin. These fish are also notable for their ability to produce electric fields, which they use for navigation and communication. Some species, like the black ghost knifefish, are popular in the aquarium trade due to their striking appearance and interesting behavior.