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Fig.1. Electric eel Electrophorus electricus — the inhabitant of the turbid waters of the Amazon and Orinoco
Fish moves in waves curving body, or at least the tail. And if she floats like a broom, working mainly in the anal fin, is most likely an electric fish, and it is better to stay away from her, especially from the acne. The South American electric eel Electrophorus electricus — a fearsome predator (Fig. 1). Adult fish generates a discharge voltage in hundreds of volts, creating around the eel's strong electric field. This is enough to immobilize large prey and to protect themselves from other predator. People from the ranks of acne very rarely die because of a small current (about 1 A) and short pulse: it lasts only 1 MS, a hundred times less than the fast blinking.
However, the high voltage causes a reduction in the numbness and painful muscles. Sometimes discomfort may persist for several hours. In other words, it is floating a Taser. None of the electric fish has a similar power. For example, the Mediterranean electric rays capable of discharge with a voltage of no more than 50-60 and a current of several amperes. Four fifths of the bodies of the South American eel, and he can grow up to three meters, employs electric organs. Unlike most electric fish, E. electricus three such bodies: the body of the sax, on hunter and the main electric organ (Fig. 2).
Fig.2. (1) Electrical organs occupy nearly 4/5 of the body of acne. (2) On cross-section are seen the cells of the electric organs is the electrolytes Packed in columns. (3) When the motor neuron innervates electronic, the action potential only occurs on the "back" of the membrane, which is connected to the axon. As a result, in the cell there is a pulse with a voltage of 150 mV.
They differ in their ability to produce electricity and perform different functions. The body of the sax constantly generates pulses of low voltage of about 10 V, creating around eel weak homogeneous electric field, and serves for orientation in the dark, in murky water in the bottom Bush. Because acne, despite the natural flexibility during motion is kept straight, so as not to distort the field around themselves and not to create interference to electrolocation. The body of the hunter and the main electric organ generate strong electrical discharges, they are designed for hunting and protection. Electric organs represent modified muscle tissue composed of specialized cells called electrolytes. They produce electricity due to its asymmetry. Each cell resembles a ribbon of length 4 cm, height 1.5 mm and a thickness of 100 µm. Cells stacked in piles along the long side flanks of the fish. On the membrane, directed towards the tail of the fish, located nerve endings of motor neurons: electronic, after all, derived striated muscle fibers.
Like all eukaryotic cells, electrolytes supported on the membrane potential difference of about -85 mV, which is achieved by active transport of sodium ions out of the cell via the sodium-potassium pump. When electronic signal motor neuron, nerve endings emit a portion of acetylcholine opens an ion channel, the sodium ions rush inside the cell, and the potential difference becomes equal to +65 mV. But these events occur only on the membrane where there are nerve endings, to the other end of the long electrocity acetylcholine does not reach. As a result, the cell generates tiny discharge capacity of 150 mV. Since electrolytes are thousands and they all are innervated by synchronous, the overall momentum reaches several hundreds of volts (Fig. 2).
E. electricus has attracted the attention of Professor, Vanderbilt University (USA) Kenneth Catania, an expert on sensory systems and behavior of mammals. He watched the young electric eels in the aquarium and noticed that the acne, paralyzing, and seizing the prey, often bends around it, so that the victim is between the head and the tail of the beast. Many researchers have described similar behavior. Catania wondered why fish goes. For three years he studied the methods of hunting of the South American eel and found the answer ("Current Biology",2015, 25, 2889-2898 doi:10.1016/j.cub.2015.09.036). In his opinion, the reason for this behavior lies in the electrical properties of acne. Since the main current generator of E. electricus, the main electric organ that extends along the fish body, its positive and negative poles (head and tail) separated from each other. Therefore, in the first approximation, the electric eel can be represented as a dipole.
generally, eels hunt small fish. They swim side by side with a potential victim, and then erupt in a series of short electrical pulses (duration of 3-4 MS, the frequency is about 400 Hz). A typical attack of acne monopolar, education of the local electric field around the victim provides a positively charged head. Voltage of about 600 V is enough to briefly immobilize the prey and grab it. But to grasp — not to eat, and at this stage there are often problems. Electric eel swallows without chewing, and fish may be too large, which often happens if the predator has not grown (length of small eels only 10-15 cm). She might have thorns, or it will be no fish and a large crayfish. This prey to swallow from the head, which requires a back to catch up with her. But the sacrifice to this point usually comes and will run away as soon as the acne unclench jaws. To apprehend an elusive meal, you must stun it for long, however acne can not increase the capacity of its electric body and the discharge rate. And then he changes the position of the body in such a way that the clamped teeth extraction is between his head and tail. This position theoretically allows him to double the strength of the electric field created around the victim, to immobilize her for a long time and without interference to swallow (Fig. 3).
Fig.3. The lines of force of the electric field that surrounds the straightened and bent the eel. The density of the lines corresponds to the field strength. According to Kenneth Catania, the real picture is likely to differ from this ideal model
To test their hypothesis, Kenneth Catania used the prepared fish from whose mouth protruded laterally at a right angle to the measuring electrodes. Acne takes such a dummy as prey, but the electrodes interfere with swallowing. The experimenter, pulling the wire may cause flutter fish, eel sees this as an attempt to escape and curl around the prey. In addition, Catania has developed a clever device that allows you to measure the voltage of electrical discharges of an eel and the contraction of the muscles that these discharges cause production — Pisces or cancer (Fig. 4).
Fig.4. Acne deafened and grabbed prey, but swallow couldn't and squeezed the fish between the head and the tail. The instruments measure the strength and frequency of electric pulses of acne and transmits the same impulses to the muscle preparation (fish or tail cancer). Other devices record the frequency and force of muscle contractions
Catania worked with three older eels with a length of 65, 90 and 120 cm and with five young specimens 10-15 cm in length; they all hunted the same way. Measurements confirmed that eels, bent, can almost double the strength of the electric field around the prey (Fig. 5).
Fig.5. Hunting electric eel. 1. Acne stuns the fish high-voltage discharge with a pulse frequency of about 400 Hz. Pulses marked with dashes in the lower part of the figure. 2. Captured fish beats, and her every movement a predator responds to a single electric discharge. 3-4. Acne is bent so that his head and tail were opposite each other, and generates a series of high-voltage discharges of different duration with a frequency of about 100 Hz. 5-6. In less than 500 MS after a series of pulses acne produces a paralyzed fish and inverts it so that it was convenient to swallow. The action is accompanied by high voltage discharges
At the beginning of the studies of Catania proved that electrical discharges of an eel act on efferent, that is coming from the brain to the periphery motor neurons of the victim, causing a contraction of all its muscles. The higher the voltage, the stronger the effect. Percutaneous stimulation of the efferent motor neurons causes rapid muscle fatigue. This effect is well familiar to physicians who use such a procedure for the activation of skeletal muscles in patients with a damaged nervous system. Pulses of acne determine the frequency of muscle contraction of 100 Hz, and the victim out of steam pretty quickly. The attack of the electric eel is quite possible to compare with the effect of the nerve poison curare or alpha-bungarotoxin (neurotoxin from the venom of the South China mnogoplanovo krait Bungarus multicinctus). However, some victims may be sufficiently resistant to the action of electrical discharges.
The ponies watched the battle with cancer that lasted nearly a minute, the eel was shot multiple times.
According to Kenneth Catania, a similar hunting behaviour could arise from ancestral species that were forced to bend when fighting with large, strong prey. Now they do it on their own volition. From a physical point of view, this effect is quite understandable. Surprisingly different: the behavior and anatomy of the electric eel have evolved in such a way that it can take advantage of this effect.
Author: N. L.Resnik
Source: "Chemistry and life" №4 2016
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