For the first time, scientists have assembled the complete genome of an electric fish—the potent South American electric eel—and in doing so have identified something much larger: Exactly how this fish, along with electric fish from other families, evolved to create their jolt-delivering organ. The findings, out of universities in Washington, Wisconsin, and Texas, touch on six lineages comprising hundreds of electric fish. They evolved separately to develop this electric organ, a phenomenon known as convergent evolution, reports Phys.org. Researchers assembled genetic sequences from three other lineages to confirm that the fish used "the same genetic tools"—a set of about 30 genes, a researcher tells NPR—to do so. "It seems like there are limited ways to build an electric organ," he says. "And that's sort of a surprising finding ... you wouldn't necessarily have expected that."
All muscle cells have electrical potential, but in these six lineages, certain ones evolved over millions of years into a different, larger cell known as an electrocyte, which produces far higher voltages. Those cells are arranged in the electric organ "much like batteries stacked in series in a flashlight," and they fire in unison. Another researcher describes the 6-foot-long electric eel as a 6-inch fish attached to a 5-1/2-foot cattle prod. Researchers hope that, building off these findings, we some day might be able to create and embed tiny electric organs in other creatures—including humans. They could power medical devices like pacemakers, eliminating the need to have a battery do so. (Read more eel stories.)