In an age with no wires, no batteries, and no human understanding of what electricity even was, there was already an animal in the sea capable of paralyzing another creature in an instant. It is not a monster out of legend but a real fish living in the ocean.
When prey comes near, this flat-bodied, slow-moving creature does not necessarily have to give chase. It need only wait until the other animal is at a suitable distance, and then release an electric current from within its body, which may be enough to stun it. This is the electric ray. The weapon the electric ray uses is not a tool acquired from outside but a special organ growing inside its own body. Some electric rays generate voltages of up to 220 volts, which gives this seemingly soft and clumsy sea animal a capacity for defense and for hunting that is not at all what one would expect.
A generator hidden inside the body
Electric rays are flat cartilaginous fish. They generally have a rounded pectoral disc, a thick and soft body, and skin without the sharp spines people tend to imagine. Their tails are strong, their tail fins well developed, and the mouth, nostrils and five pairs of gill slits are on the underside of the body.
From the outside, an electric ray is hard to associate with the generation of electricity, and the real secret lies at the base of the pectoral fins. On each side, left and right, the electric ray has a large kidney-shaped electric organ. These organs are not a simple single “battery” but are made up of great numbers of specialized structures. Inside them the cells are packed closely together, forming hexagonal columns rather like a honeycomb. Each column contains more than 500 to 1,000 cells, which derive from specialized muscle tissue, and when a nerve signal arrives, large numbers of cells can produce a difference in electrical potential at the same moment.
The effect produced by any single cell is not striking. But when vast numbers of cells are arranged in a particular way and act together, the result is something else entirely, and a fish comes to have a biological power source of its own.
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Some electric rays can discharge at up to 220 volts. The animal does not store electricity in its body waiting to use it; it relies on a special physiological structure to generate a discharge when one is needed. The current can be used to stun prey, and it can serve as a means of defense.
Electric rays generally move slowly. Unlike some rays, which rely mainly on their pectoral fins to swim, the electric ray propels itself with its tail. They can live in shallow coastal waters and can also be found at depths of 1,000 meters. For an animal that is not agile, an electric current becomes a very unusual means of survival.
It can lie in wait beneath sand or other seabed material for an invertebrate or a small fish to come near, and the prey may have no idea of the danger at all. In the next moment, a discharge from the electric ray’s body may leave it unable to move. This kind of hunt does not even require a high-speed pursuit.
To the earliest humans, it looked like a creature of magic
In the era before human beings understood electricity, this animal was already making people feel a force they could not explain. In ancient natural history records, the electric ray was described as a creature with magical powers. People then had no concept of an electric current, and did not know that a fish could contain an organ devoted to producing electricity. They knew only one thing: sometimes, without actually touching the fish, a person might feel numb. Such a phenomenon was naturally easy to regard at the time as some kind of mysterious power, and the ancient Greeks used electric rays to relieve the pain of childbirth and of surgery.
The electric ray even found its way into the writings of the philosophers of antiquity. In Plato’s Meno, Meno uses the electric ray as a comparison to describe the baffling questions Socrates asks. The comparison was not made without reason. People at the time already knew that the electric ray had the power to numb and to shock. The electric ray therefore became a vivid symbol: a person who had thought he held the answer suddenly runs into some force that leaves him confused and brought to a halt.
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