Electric ray

Lore & Background

Electric rays have a rounded pectoral disc with two moderately large rounded-angular dorsal fins, and a stout muscular tail with a well-developed caudal fin. The body is thick and flabby, with soft loose skin and no dermal denticles or thorns. A pair of kidney-shaped electric organs are at the base of the pectoral fins. They are sluggish and slow-moving, propelling themselves with their tails, not by using their pectoral fins as other rays do. They feed on invertebrates and small fish, lying in wait for prey below the sand or other substrate, using their electricity to stun and capture it. The electrogenic properties of electric rays have been known since antiquity. The ancient Greeks used electric rays to numb the pain of childbirth and operations. In his dialogue Meno, Plato has the character Meno accuse Socrates of 'stunning' people with his puzzling questions, in a manner similar to the way the torpedo fish stuns with electricity. Scribonius Largus, a Roman physician, recorded the use of torpedo fish for treatment of headaches and gout in his Compositiones Medicae of 46 AD. In the 1770s the electric organs of the torpedo ray were the subject of Royal Society papers by John Walsh and John Hunter. These appear to have influenced the thinking of Luigi Galvani and Alessandro Volta.

Reader's Guide

Electric rays hold a significant place in the history of science, particularly in the development of electrophysiology and electrochemistry. Their ability to produce electricity was known since antiquity, but it was not until the 1770s that systematic study by John Walsh and John Hunter led to papers before the Royal Society. These investigations appear to have influenced Luigi Galvani and Alessandro Volta, founders of electrophysiology and electrochemistry. Henry Cavendish further demonstrated the electrical nature of the discharge by building an artificial ray using Leyden jars. The torpedo fish also appears in premodern natural histories as a magical creature, and its ability to numb fishermen without seeming to touch them was a significant source of evidence for the belief in occult qualities in nature before the discovery of electricity. The torpedo undersea weapon is named after the genus Torpedo. The electric organs consist of hexagonal columns of modified striated muscle, adapted from the branchial muscles. In marine fish, these batteries are connected as a parallel circuit, whereas freshwater batteries are arranged in series, allowing freshwater rays to transmit higher voltage discharges.

Did You Know?

• The name 'torpedo' comes from the Latin torpere, meaning 'to be stiffened or paralyzed'.
• The ancient Greeks used electric rays to numb the pain of childbirth and operations.
• Henry Cavendish built an artificial ray using fish-shaped Leyden jars to mimic the electric ray's behavior.