The Shocking Truth About Electric Fish

For the first time, the genome of the electric eel has been sequenced. Image: Courtesy of Michigan State University

Scientists have found a potential answer to the question of how electric fish evolved six times in separate and distant parts of the world.

The work establishes the genetic basis for the electric organ, an anatomical feature found only in fish and which evolved independently in environments ranging from the flooded forests of the Amazon to the murky seas.

“These fish have converted a muscle to an electric organ,” says Michael Sussman of the University of Wisconsin-Madison.

The study published in the journal Science provides evidence to support the idea that the six electric fish lineages, all of which evolved independently, used essentially the same genes and developmental and cellular pathways to make an electric organ, needed for defense, hunting, navigation and communication.

“What is amazing is that the electric organ arose independently six times in the course of evolutionary history,” says Lindsay Traeger, a UW-Madison graduate student in genetics and a co-lead author of the new report along with Jason Gallant, an assistant professor of zoology at Michigan State University.

“The surprising result of our study is that electric fish seem to use the same ‘genetic toolbox’ to build their electric organ,” despite the fact that they evolved independently.

Electric fish have long fascinated humans. The ancient Egyptians used the torpedo, an electric marine ray, in an early form of electrotherapy to treat epilepsy.

Much of what Benjamin Franklin and other pioneering scientists learned about electricity came from studies of electric fish. In Victorian times, parties were organised where guests would form a chain to experience the shock of an electric fish.

The electric organ is used by fish in murky environments to communicate with mates, navigate, stun prey and as a shocking defense, probably a reason why the muddy Amazon and its tributaries teem with electric fish, including the electric eel, the most potent of them all.

Not really an eel but a fish more closely related to the catfish, the electric eel produces a jolting electric field of up to 600 volts.

All muscle cells have electrical potential. Simple contraction of a muscle will release a small amount of voltage. But at least 100 million years ago some fish began to amplify that potential by evolving from muscle cells another type of cell called an electrocyte.

“I consider ‘exotic’ organisms such as the electric fish to be one of nature’s wonders and an important ‘gift’ to humanity,” says Sussman.

“Our study demonstrates nature’s creative powers and its parsimony, using the same genetic and developmental tools to invent an adaptive trait time and again in widely disparate environments.

“By learning how nature does this, we may be able to manipulate the process with muscle in other organisms and, in the near future, perhaps use the tools of synthetic biology to create electrocytes for generating electrical power in bionic devices within the human body or for uses we have not thought of yet.”

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