The current density is greatest directly above or below the ray's electric organs. When a foraging torpedo ray detects prey it therefore swims forward and upward, exposing its ventral surface towards the fish while emitting low-frequency voltage pulses. The currents passing through the victim's body excite its nerves and muscles, stunning it and immobilizing it, whereupon the torpedo descends over it and consumes it while continuing to emit pulses.
It is well known that a large T. nobiliana can deliver a painful and stunning shock to an adult human being. Aside from the obvious life-threatening aspects of being disoriented underwater, can the shock be fatal? The lowest threshold for cardiac arrest or ventricular fibrillation in a human occurs for current following a left-hand-to-either-foot path through the body. In an underwater environment the total body impedance (skin plus internal) for this current path is certainly no less than 500 ohms. A 100 V pulse, which is larger than average for nobiliana, would therefore generate a maximum body current of 200 mA. Thresholds for physiological effects induced by electric currents are functions of both their magnitudes and durations. For the average adult experiencing a 200 mA left-hand-to-either-foot current, the threshold for muscular contractions causing breathing difficulties is approximately 50 ms, while the threshold for ventricular fibrillation is about 400 ms. For a 220 V pulse (maximum observed) the breathing-difficulty and fibrillation thresholds are about 20 ms and 200 ms respectively. But the voltage pulses generated by nobiliana have a duration of only 5 ms. Because of the statistically-derived nature of the above thresholds, it would not be surprising if the electric shock from a large Atlantic torpedo were to induce (temporary) breathing difficulties in some individuals. Ventricular fibrillation or cardiac arrest, however, are extremely unlikely.
