I am thoroughly enjoying Ed Yong’s book An Immense World, which explores how living creatures perceive the world. There’s a really interesting chapter on electroreception. I need this to better understand—it’s wildly interesting, and for you—I don’t know why you need it 🙂 but it’s really interesting, hit like if you agree it’s interesting.
Well, everyone probably knows about the electric eel, which with its electric organs can create a potential difference (voltage) of up to 860 V and a current strength of up to 40 mA—enough to lay down a horse. Literally, this was tested on horses in 1880 by Alexander von Humboldt, ending up with dead horses.
But the most interesting thing is not that they are just swimming batteries. It’s interesting that many animals have electroreception—they can sense their immediate surroundings just as a theremin does. Since electroreception requires a conductive environment, these are all aquatic creatures—catfish, mormyrids, notopterids and gymnotids. Specifically, the last group includes eels and knifefish. The Black Ghost or Knifefish—a popular aquarium fish—generates a small voltage, but not to kill, rather to “see” with its entire body and see through sand and objects.
This feature is called active electrolocation. Both weakly and strongly electric fish create around themselves a characteristic dipole electric field. If there are no objects in the water around the dipole, it is symmetrical. Its configuration depends on the water conductivity and distortions when an object with different conductivity from water enters the electric field. In other words, by using its electric field (generated by discharges) and electroreceptors, the fish feels disturbances in the field when something enters it. An electric potential redistribution occurs on the surface of the body, which helps them determine the direction of impact or “invasion,” the size of the object, etc. The black knifefish has 14000 electroreceptors distributed over its body. The organ of electroreception consists of specialized spinal nerves that are spontaneously activated and are the fastest firing cells known in the nervous system of any animal—they continuously produce electrical signals at a rate of more than 2000 times per second.
Considering that the speed of electromagnetic waves in water reaches 225,000 km/s, electroreception allows weakly and strongly electric fish to almost instantaneously react to field distortion (by fleeing or attacking), while signals from other sensory systems may be delayed in time. Unlike the ultrasound of bats, which I wrote about in the last post, here the electric fields do not move. Moreover, the fish can change the intensity of the electric field to enhance sensitivity and distance. Yes, it does take their energy, so they do it when necessary.
There were experiments when a knifefish distinguished a sealed opaque pot from another similar one by their contents.
It gets even more interesting. Since they can sense each other’s fields, they have adapted to use these fields for communication. Unlike everything else, radio communication is the most reliable, and here it’s essentially radio. The only problem is distance, but compared with the size of the fish, it’s still decent. Experiments show that electric fish are sensitive to changes in the field with a resolution of 1/1000000 second. They themselves emit signals with a resolution of about 1/2000 second.
Some species of fish can pulse their fields specifically for communication, and the shape of this pulsation—the duration and how the voltage changes over time—contains information about what kind of fish, sex, status, and sometimes identity. But timing—that is, a larger form determining rhythm, regularity, etc.—determines the essence of the message. There are “words” in this language that mean “let’s hurry,” and others about love.
For example, as I mentioned earlier, research by neurobiologist Ted Bullock has shown that the electrical field of the black knifefish pulses every 0.001 second, deviating by no more than 0.00000014 second. In other words, these are the most accurate biological clocks in the animal kingdom. If you attach a clock to the fish, it would be off by an hour per year. Moreover, the fish’s “radio” uses frequency modulation (FM) to transmit messages.
It turns out that electroreception is not only present in electric fish, but also in many others in the water. For example, sharks. They have special organs on their noses called the ampullae of Lorenzini. This allows them to capture electric fields and detect extremely small changes in their intensity. These organs got their name because in 1678, this doctor wrote “what the hell is on their noses,” and a biologist R.W.Murray answered him only 300 years later, but by then these things had already been named.
So, with these ampullae of Lorenzini organs, sharks and rays feel living beings, even if they are not visible—for example, when the prey is hiding in the sand. But how, sharks can’t generate a field, unlike the knifefish or eel? Therefore, this is called passive electroreception. All living beings generate microvoltages, and the shark’s organs feel this at a short distance. This discovery is already 50 years old, but for some reason they didn’t tell us such interesting things at school. For example, hammerhead sharks can detect an electric field of 1 nanovolt (1/1000000000 volt) per centimeter of water.
Among a large group of mammals, electroreception is known only in the Australian platypus and is suspected in the echidna. The platypus has 50000 receptors, and by the same principle as the shark, searches for food in murky water or on the bottom under sand. Besides everything else, its eyes, ears, and nose are closed under water, so it uses only electroreception. There was also an interesting experiment with bees. If you look at their world through organs of electroreception, there would be an entire universe. For example, flowers have a negative charge, bees—a positive (because they lose electrons in flight), and according to the experiment, bees can distinguish artificial flowers with different charges. Bees don’t have any ampullae of Lorenzini, but they do have sensitive hairs on their skin.
Sometimes you wonder how skillfully nature uses the laws of physics.
Hi, I'm Rauf Aliev. 