How electric eels developed power to deliver jolts

Sequencing the genome of electric eels for the first time, researchers have found that fishes with electric organs have evolved six times in the history of evolution to produce electricity outside of their bodies.

Electric eels can deliver a jolt several times more powerful than the current from a standard household electrical outlet.

"It is truly exciting to find that complex structures like the electric organ, which evolved completely independently in six groups of fish, seems to share the same genetic toolkit," said Jason Gallant, a zoologist at Michigan State University in the US.

"Biologists are starting to learn, using genomics, that evolution makes similar structures from the same starting materials, even if the organisms are not even closely related," Gallant added.

Worldwide, there are hundreds of species of electric fish in six broad lineages.

All muscle and nerve cells have electrical potential. Simple contraction of a muscle will release a small amount of voltage. But between 100 and 200 million years ago, some fish began to amplify that potential by evolving electrocytes from muscle cells, organised in sequence and capable of generating much higher voltages than those used to make muscles work.

"Evolution has removed the ability of muscle cells to contract and changed the distribution of proteins in the cell membrane; now all electrocytes do is push ions across a membrane to create a massive flow of positive charge," Lindsay Traeger from the University of Wisconsin-Madison in the US said.

The "in-series alignment" of the electrocytes and unique polarity of each cell allows for the "summation of voltages, much like batteries stacked in series in a flashlight," said Michael Sussman from the University of Wisconsin-Madison.

The additional current required for the power comes from the fact that an eel body contains many millions of such "batteries" working together and firing their electrical discharge simultaneously.

The study appeared in the journal Science.