There are about 250 species in this order of freshwater fish, known as electric knifefish, spread across five families. They live in rivers and streams from southern Mexico to northern Argentina.

These fish have long, slender bodies that resemble the blade of a knife. Unlike many other fish, they usually lack a dorsal (top) fin. Instead, they swim by rippling their long anal (bottom) fin, which runs along much of their body. This allows them to glide smoothly forward—or even backward.

What makes Gymnotiformes especially interesting is their ability to produce electric fields. They use these weak electric signals to:

• navigate in dark or muddy water
• find food, such as insects and small fish
• communicate with other fish

Some species, like the electric eel, can produce much stronger electric shocks to defend themselves or stun prey.

Most Gymnotiformes are nocturnal, meaning they are active at night. During the day, they often hide among plants, roots, or rocks.