Most people know that electricity and water don’t mix, but it’s not a problem for fish that produce their own electricity. The best-known electric fish is probably the electric eel, but it is far from the only “shocking” creature underwater. In fact, the electric eel, a single species that dwells only in the rivers of South America, is outnumbered by more than 60 species of electric rays that live in the oceans.
Like the electric eel, electric rays use electricity both to catch prey and to defend itself against predators. Its shock maxes out at about 45 volts, hardly the eel’s impressive 600 volts. But these rays don’t stop with just a single surge. They deliver more than 400 rapid pulses in a row, lasting five milliseconds each. A single second for a prey wrapped in the fins of these rays can mean 300 rapid-fire shocks, with faster pulses in warmer water that allow some rays to deliver as much as a kilowatt of power in one attack. It’s enough to knock a human off his feet, though it won’t kill someone as the eel can do.
The rays and eel produce electricity in different ways. Rays produce electricity through modified muscle cells called electrocytes. Like a row of batteries, stimulated electrocytes move electrically charged atoms (ions) across the cell membrane, creating a combined electric discharge. The eel, meanwhile, sends positively-charged sodium through its electric organs, which reverses their charge and generates a current. This can only work in fresh water; otherwise the eel’s positively charged head would short out with its negatively charged tail, killing the eel as effectively as these shocking creatures kill their own prey.