[1] Many species are specialized for life in the deep (more than 20 m or 66 ft) swiftly moving waters of large river channels, like that of the Amazon and its major tributaries[2] where they have been observed swimming vertically.

The anal fin originates at the isthmus (the strip of flesh on the ventral surface between the gill covers).

Humboldtichthys kirschbaumi (formerly genus Ellisella) from Upper Miocene of Bolivia is the only fossil gymnotiform.

[1] These fish have a tone-like electric organ discharge (EOD) that occurs monophasically.

There are 30 living species of glass knifefish, grouped into six genera:[5] This Gymnotiformes-related article is a stub.