How Electric Eels Generate their Shock?

 by Sam Kalra

Exclusively native to the murky pools and slow-moving streams of the Amazon and Orinoco rivers, electric eels are the slippery predators of South America. Despite their eel-like shape, these creatures are found in the order of Gymnotiformes and are scientifically referred to as ‘knifefish’. Electric eels can reach lengths of 2.4 metres and can weigh around 100 kg yet, it is a deadly shock of up to 860 volts that is their most impressive feature. How can an organism pack such a punch?

A knifefish’s vital organs are situated in the front 20% of its body, while the rest of the eel consists of three organs - the Main organ, Hunter’s organ and Sach’s organ. Inside, thousands of disc-like, flattened cells called electrocytes are stacked in columns along the length of the eel. Potassium and sodium ions are pumped out of these cells to maintain a positive charge outside the cell and a negative charge inside. However, when hunting or in danger, the knifefish sends nerve impulses to these electrocytes which in turn causes positively charged sodium ions to build up outside the cell. The influx of Na⁺ ions back into the electrocyte triggers a potential difference across the cell. Intelligently, the nerve signals are coordinated so that they arrive at the electrolytes at exactly the same time - the stacked cells act as a battery and a huge potential difference is induced across the whole organism. Such high voltages, when discharged on prey, disables its nervous system, enabling easy capture. 

You might wonder why these creatures do not electrocute themselves while hunting. Possible theories suggest that the current leaves their body before it can damage the fish or even that they can stiffen their bodies before the shock to protect their vital organs - but there is little research to back these propositions.