Electric Eels: The 860-Volt Fish That Inspired the First Battery

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In 1800, Alexander von Humboldt watched fishers drive wild horses into a muddy South American pond until electric eels rose from the water and shocked two of them into drowning. This episode explains the animal behind that scene, starting with a correction: electric eels are not eels at all but neotropical knifefishes. For 250 years, from Carl Linnaeus in 1766 onward, science assumed there was a single species. In 2019 C. David de Santana and his team proved there are three, and one of them, Electrophorus voltai, delivers 860 volts.

The body that produces that shock is strange. Every vital organ sits in the front 20 percent, and the rest is given over to three electric organs built from about 6,000 modified muscle cells stacked in series like batteries in a flashlight. The episode covers how a nerve signal turns chemistry into current in two millisecond pulses, why a fish that lives in water will drown if it cannot gulp air, and how eels hunt in packs and nest in foam. It closes with the line from eel anatomy to Volta's battery and to artificial cells that may one day power medical implants.

• Each electrocyte produces roughly a tenth of a volt, and the eel stacks thousands of them in series so the shock can push through poorly conducting fresh water.
• Sachs's organ puts out only about 10 volts, which the eel uses like radar to navigate and find prey in murky water without draining its main supply.
• Electric eels surface for air about every two minutes, absorb oxygen through the lining of the mouth, and release most of their carbon dioxide through the skin.
• Researchers saw groups of eels herd shoals of tetras into the shallows and strike together, while males guard foam nests of saliva holding around 1,200 eggs.
• John Hunter dissected an eel in 1775 and found organs built like a stack of coins, the structure Alessandro Volta copied in 1800 with zinc, copper, and brine-soaked cloth.