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Electric ray

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Electric rays are a specialized group of cartilaginous fish. They belong to the biological order Torpediniformes. These animals are defined by their ability to produce an electric discharge. They use this electricity to stun prey and for defense. There are 69 known species divided into four main families. These fish have flat, thick, and flabby bodies. Their skin is soft and loose. Unlike many other rays, they lack dermal denticles or thorns.

The biological mechanism of their power comes from specialized electric organs. These organs are shaped like kidneys and sit at the base of the pectoral fins. Each organ is composed of many hexagonal columns arranged in a honeycomb formation. These columns contain between 500 and over 1,000 tiny plaques. These plaques are actually modified striated muscle cells. They are adapted from the branchial muscles, which are the muscles of the gill arches. Nerves signal the organ to discharge by branching out to these plaques. When the signal arrives, the current passes from the lower surface to the upper surface of the fish.

How these batteries are connected depends on the water environment. In marine fish, the electric organs are connected as a parallel circuit. However, freshwater rays arrange their batteries in a series circuit. This structural difference is very important for their survival. Freshwater does not conduct electricity as well as saltwater. By using a series arrangement, freshwater rays can transmit a much higher voltage. This allows them to remain effective hunters even in less conductive water.

There are different types of electric rays with different hunting styles. The family Torpedinidae, or torpedo rays, typically feeds on large prey. They use their electricity to stun these animals and then swallow them whole. In contrast, the Narcinidae family specializes in much smaller prey. These rays often hunt animals that live in or on the bottom substrate. While both families use electricity for defense, it is not yet clear if Narcinids use it for feeding. Other families in the order include the Platyrhinidae, known as thornbacks, and the Hypnidae, called coffin rays.

Humans have been fascinated by these fish since ancient times. The Greeks used electric rays to numb pain during operations and childbirth. In 46 AD, the Roman physician Scribonius Largus recorded using them to treat gout and headaches. Even the philosopher Plato mentioned the fish in his dialogue, Meno. He used the fish as a metaphor for how Socrates could stun people with questions. In 1773, Henry Cavendish even built an artificial ray. He used fish-shaped Leyden jars to mimic the electric behavior of the real animal.

The study of these rays helped create modern science. In the 1770s, researchers John Walsh and John Hunter published papers on the electric organs. Their work influenced Luigi Galvani and Alessandro Volta. These two men are considered the founders of electrophysiology and electrochemistry. The voltage produced by these rays varies significantly by species. Some narcinids produce only 8 volts. However, the Atlantic torpedo, Torpedo nobiliana, can reach a powerful 220 volts.

In many cultures, these rays were seen as magical or occult. Before people understood electricity, the fish seemed to have supernatural powers. Fishermen were often numbed by the rays without even being touched. This led to many legends in premodern natural histories. Today, we understand that this is a biological process rather than magic. These rays remain vital members of their ecosystems, from shallow coasts to deep waters. They move slowly by using their muscular tails rather than their fins.

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