Gymnotus

The banded knifefish, Gymnotus carapo, is a gymnotid knifefish recorded across Central and South America, from Mexico to Argentina. Several species once considered G. carapo have been described since 1994, and its massive natural range will likely turn out to be far more restricted. It uses a weak electric field to navigate and communicate, and a modified swimbladder acts as an accessory breathing organ. It grows to 60 cm and is sensitive to many medications, particularly copper.

The zebra knifefish, Gymnotus pedanopterus, is a gymnotid knifefish from Peru and Brazil, one of over 20 Gymnotus species described since 1994. It grows to at least 28 cm and inhabits sluggish or still, turbid waters. Like other gymnotids it produces a weak electric field that it uses to navigate and communicate, and it is sensitive to many aquarium medications, particularly those containing copper.