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How the ghost knifefish became the fastest electrical discharger in the animal kingdom

The South American ghost knifefish (pictured) may not be the brightest spark in the animal kingdom, but it certainly is the most persistent. It has a specialized organ in its tail containing a small group of cells that can discharge electricity at frequencies approaching 2000 times per second, the fastest in the animal kingdom.

To find out how the ghost knifefish does this, researchers compared the gene encoding the voltage-gated sodium channel, a protein essential for generating electrical signals, in the ghost knifefish with those of the glass knifefish, an electric relative, and the channel catfish, a nonelectric species. They found that the gene was duplicated in ghost knifefish approximately 14.5 million years ago, then acquired several mutations over the subsequent 2 million years, which made the channel fire more frequently and led to it being synthesized by nerve cells in the spinal cord as well as in muscle cells, the team reports today in PLOS Biology. The fish uses these electrical sparks to navigate, detect objects, and communicate.

The scientists say the findings could provide new clues about the genetic basis of epilepsy and certain inherited muscle diseases, which are associated with mutations in sodium channel genes.