Gymnotus electricus; Print; Gymnotus is a genus of Neotropical freshwater fish in the family Gymnotidae found widely in South America; Central America and southern Mexico (36th parallel south to 18th parallel north). The greatest species richness is found in the Amazon basin.They are sometimes referred to by the English name banded knifefish; although this typically is reserved for the most widespread species; G. carapo. Overall Gymnotus is the most widespread genus in the order Gymnotiformes.