Friday, 4 July 2014 | MYT 9:30 PM

Muscle power: Shocking secrets of electric fish unleashed

Using genetic studies, scientists reveal how these exotic creatures develop their unique electricity-generating organs that can unleash a wicked jolt.

As astonishing as the bioluminescence found in some insects and sea creatures and echolocation in bats and whales, the wonder of nature that is the electric fish has long fascinated scientists and nature lovers alike. They are the only animals so far that have been found with the ability to zap others.

Hundreds of species of electric fish exist worldwide and they are divided into six main groups: South American knife fishes, African electric catfish, African elephant fish, stargazers, some skates and some rays. And though we have known of their existence for a long time, the mechanism behind their ability to generate electricity has never been fully understood until now.

The power of fish: Just two of the hundreds of species of fish known to be able to generate electricity. Above, most revered and powerful of them all, is the electric eel (Electrophorus electricus), which despite its name is not an eel but a type of knife fish. Below, a more typical member of the knife fish group, with its characteristic elongated anal fin that runs along the underside of its body, the black ghost knifefish (Apteronotus albifrons) that's popularly kept as pets by fish aquarium enthusiasts. 

In a study published in Science on June 26, researchers into this mystery unveil a genetic blueprint of the electric eel — a fearsome denizen of South America that can zap you with an electric field of up to 600 volts — as well as detailed genetic data on two other types of electric fish.

The new study finds that various electric fish species rely on the same genes and biological pathways to build their electric organs from skeletal muscle, despite the differing appearance and location of these special organs on their bodies — and despite their different evolutionary histories and geographical locations.

No matter if they evolved in far-flung locales like the muddy waters of the Amazon or murky lakes in Africa, they all seem to have reached into the same "genetic toolbox" to fashion their electricity-generating organ, the study said.

Legacy of electricity: The 'nose' of the Peters' elephant nose fish (Gnathonemus petersii), shown above, is not actually a nose but an extension of its mouth that's covered in sensitive electro-receptors to help it with navigation, finding prey and communication. Below is the lesser electric ray (Narcine bancroftii), which uses its electric organs, running from the front of its eyes to the rear end of its disc-like body, to stun its prey before going in for the kill.

"It really is something truly unique in the animal kingdom," Michigan State University zoology professor Jason Gallant said. "This only arose in fish because water is a conductor of electricity while air is not. Thus, birds or terrestrial animals could not come up with this," University of Wisconsin biochemistry professor Michael Sussman added. 

Not all electric fish have equal electric power, however. Fish with weak electric power use it to navigate in dim waters and communicate with one another. Those like the electric eel — a serpentine freshwater predator up to 2.4m long that’s not a true eel but rather a member of the knifefish family — possess a powerful jolt that they use to stun or kill prey and repel enemies.

Modified muscle

Scientists have wondered about how these fish first acquired electric powers and how this characteristic emerged six times in groups not closely related to one another.

"Electric organs start out their lives as muscle precursor cells. Through a series of developmental steps, they become larger, more electrically excitable and lose their ability to contract," Gallant said, adding that scientists think the electric organ first appeared in fish between 150 million and 200 million years ago.

All muscle cells have electrical potential because any muscle contraction releases a small amount of voltage. Certain fish exploited that by transforming ordinary muscle cells into a larger type of cell called an electrocyte that generates vastly higher voltages. The electric organ is made of these cells.

"Each electric organ cell makes only a small voltage, similar in magnitude to our own muscles. The secret of electric organs is that the cells are aligned in stacks and electrically insulated so that the voltages add like batteries in a series," University of Texas neuroscience professor Harold Zakon said. — Reuters

Tags / Keywords: Lifestyle , Features , electric fish


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