Mark Bowler / Electric eel (Electrophorus electricus) on white background. Controlled conditions, digital focus stack.

Mark Bowler / Electric eel (Electrophorus electricus) swimming towards the surface to breathe, Yavari area, Amazon Rainforest, Peru.

MYN / Martin Taylor / Brachyhypopomus sp., close to Manacapuru, Brazil. Meetyourneighbours.net project

Michael Pitts / Glass knifefish (Eigenmannia sp) Amazon, Brazil

Joel Sartore / Photo Ark / Glass knifefish (Eigenmannia virescens) swimming into frame, Fin-Tastic Fish, Nebraska. Captive.

Joel Sartore / Photo Ark / Electric eel (Electrophorus electricus), close-up of head. Oklahoma Aquarium. Captive.