The measurements, reported in the journal Current Biology, show that this tiny eel’s total voltage was 198 volts. The Taser-like jolt to Catania’s arm peaked at 40–50 milliamps, which is more than enough to cause a victim considerable pain, but not enough to cause permanent damage.
In real life, however, humans and animals may encounter much larger electric eels. A fish twice the size of the one used in the study would likely discharge twice as much electric current.
“As the eels get longer, their voltage and current both increase, meaning there is more electrical power,” Catania explained.
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The eels’ clever techniques for increasing the strength of their currents are helping Catania and others to better understand the science underlying electromotive forces. He suspects that the height of an eel’s leap is significant, since greater leaps may maximize a current’s jolt and conserve energy.
“Probably one reason they leap up to attack is that they may have a limited amount of energy before becoming exhausted,” Catania said. “So delivering that energy efficiently is important.”
The primary electric eel goal is to deter predators, which does not necessarily mean killing them. Catania agrees with Humboldt, who suspected that the two horses in the account from the 1800s died as a result of drowning while trapped in the water with the electric eels.
The fisherman temporarily paralyzed by the eels in the 1600s had a better outcome. His comrades boated out to him, tied him to a rope, and dragged him back to shore — wincing but alive.
“Many people have been shocked by large eels,” Catania said. “I don’t know of any report going back 200 years of anyone who was killed from the shocks. But drowning is more likely, because the eel can cause temporary paralysis.”
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The eel’s natural deterrent appears to be working.
“My guess is that electric eels are not common prey for most species,” Catania said.
These animals are also not endangered, although numbers are likely much lower than historic populations due to their deaths as by-catch and intentional killings by humans.
Human skin has little evolved resistance to the electric eel’s defense. During the study, Catania tried hard to keep his arm still, but it would reflexively pull back at times.