Power of electric eels is a natural mystery

According to the National Oceanic and Atmospheric Administration, lightning kills about 24,000 people worldwide each year. Apocalyptic thunderstorms occur when the gods were angry, or so it was thought; only during them do we mortals perceive electricity directly. Some fish, however, have no such difficulty; they not only sense the mysterious energy, but use it to locate prey.

Power of electric eels is a natural mystery

According to the National Oceanic and Atmospheric Administration, lightning kills about 24,000 people worldwide each year. Apocalyptic thunderstorms occur when the gods were angry, or so it was thought; only during them do we mortals perceive electricity directly. Some fish, however, have no such difficulty; they not only sense the mysterious energy, but use it to locate prey.

The notorious electric eel goes further; it has developed electrical sensitivity into a lethal weapon. The mysterious eel was first described by Carl Linnaeus in 1766. Ever since then, there was thought to be just one species. A paper just published, however, claims that there are at least three.

The dark-brown, snake-like fish, up to 2.5m long, live mainly in the Amazon and Orinoco waters. They are not eels nor closely related. Specialist organs generate low and high voltages. The low level ones help the fish to navigate and locate prey. The high ones deliver powerful stun-gun-type shocks — painful, but not lethal, to human intruders.

Thanks to this mysterious fish, ‘animal electricity’ became a hot topic in the 18th century. Italian scientist Luigi Galvani showed that wired-up legs of dead frogs twitch during thunderstorms. The ghoulish phenomenon would inspire Mary Shelley to write her classic novel Frankenstein.

Galvani thought that a ‘vital fluid’ was responsible for the twitching. Another Italian, Alessandro Volta, disagreed. He believed the mysterious energy didn’t come from the frogs themselves but from the wires used in experiments on them. Both theories were flawed but, in trying to prove his thesis, Volta invented the ‘voltaic pile’, the world’s first battery. Research inspired by the electric ‘eel’ had led to a technological revolution.

Animal electricity is no longer a puzzle; complex chemistry results in the build-up of ions across membranes. However, the mysterious ‘eel’ continues to fascinate scientists.

Between 2014 and 2017 a team led by Carlos de Santana, of the Smithsonian National Museum in Washington, examined 107 specimens collected from several South American countries. The voltages the fish produced were measured and tissue samples genetically tested.

Writing in Nature Communications, de Santana and colleagues, reveal the differing voltage levels, which the fish generate, correlate with DNA variations; the team’s electrical investigations have led to the discovery of two species. Differences in the shape of heads and fins had been overlooked by previous researchers. One of the species has been named after Volta. Its members can generate up to 860v. The highest level recorded previously of a fish was 650v.

In other electrifying news, scientists at the University of Washington have investigated superbolts, lightning discharges thousands of times more powerful than ‘normal’ ones. Lightning events were logged at stations worldwide since the early 2000s. The researchers examined data on two billion discharges.

Of these, 8,000 proved to be superbolts. Unlike ordinary lightning, which occurs mostly over land, superbolts are much commoner over water. They are confined largely to particular regions, one of which is the eastern north Atlantic. Normal lightning is most frequent in summer but superbolts are mainly a winter phenomenon. Scientists are at a loss to explain why the discharges occur.

- RH Holzworth et al. Global Distribution of Superbolts. Journal of Geophysical Research: Atmospheres. 2019.

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