Why eels electric

The facts are flabbergasting! Sep 10, Wallace Joinbum Sep 8, Hello Wonderopolis! I cant stop reading your website! I love it!!! Joe Bob Sep 8, Thanks for joining the discussion! We appreciate your comments! Dylan Sep 3, Sep 3, Yazminah Aug 28, Aug 28, Mattski Aug 21, Aug 21, You guys should add videos to attract even more people and it would be awesome.

Aug 16, Aug 17, Wonderopolis Jan 21, Wonder friend L May 3, Wonderopolis May 3, Audrey C Mrs. Feb 7, WOW, I really never knew that electric eels breath air. Also that they are related to catfish. But I never knew that they go to the surface every 10 minutes before going back underwater. I think it's kind of crazy that they go back out of the water like we people do. Wonderopolis Feb 8, Sarah Suo-MC Oct 12, Dear Wonderopolis, This wonder was extremely interesting!

I thought the Japan Christmas tree was phenomenal! Wonderopolis Oct 13, That amazed me I never knew they were really electric, I always thought they were just called an electric eel.

I thought that video was very cool! How did this video interest you? Wonderopolis Sep 21, Jaden Jul 9, Wow, that was so cool! I will add a comment too! Wonderopolis Jul 10, Thanks for letting us know you liked this Wonder, Jaden! Thanks for commenting, too! Dexter Jul 5, Wonderopolis Jul 5, Maria Caplin Jul 1, I love when friends teach each other about Wonderopolis thanks Meredith!!! Wonderopolis Jul 2, We couldn't agree more, Maria!

Anna B. Jul 1, Hello again! I hope that you don't mind if I ask a ton of questions! How often do you change the backround? Wonderopolis Jul 1, Hi wonderopolis!!! I found today's wonder extremely interesting. I had no idea that eels could control the amount of electricy that they produce. By the way, Anna B. I think that tomorrow's wonder might be about time zones, and I will certainly have some time, tomorrow!!!

I can't wait to see if my prediction is correct :. I think that it is so cool that electric eels can breathe air! So, where do these eels live in North America? Or do they only live in South America? Do they only live in warm climates? I bet that tomorrow's wonder will be about clocks!

And maybe how they work. Related Wonders for You to Explore Match its definition: the rate at which energy is drawn from a source that produces a flow of electricity in a circuit; expressed in volts. It has parallel circular faces joined by a curved face. Word Match Congratulations! Share results. This means the positive and negative poles the head and tail, respectively are widely separated in space.

Figure 7. Dipole field and dipole attack. A Schematic illustration of a dipole field surrounding an electric eel and its change in configuration B after the eel has brought the two poles close together.

Lines indicate electric field lines a positive test charge would experience a force tangent to the line at any point—in the direction of the negative pole. C Schematic illustration of electrodes with un-insulated wire arrows approximately 1 cm apart. D View of eel holding electrode-fish preparation tightly.

E Schematic of electrode position during trial. F Large eel presented with the pithed fish with electrodes. After capture, the experimenter manually jiggled the wire to simulate prey struggling and the eel curled to deliver multiple discharges.

Note the dramatic increase in recorded voltage, and discharge frequency, during the curl relative to the uncurled configuration from Catania, c , reproduced with permission. This would change drastically, however, if the eel were to curl and bring its tail behind and close to the prey. In such a case, the effect of the tail the negative pole would be additive because the prey would be sandwiched between the two poles and strong because the negative pole would be close , rather than subtractive and weak.

The theoretical effect of such a curling move would be to double the intensity of the electric field experienced by prey, at virtually no cost to the eel. In fact, electric eels commonly engage in this curling behavior when handling difficult prey Catania, c. Juvenile eels frequently curl when attacking any prey item, whereas adults curl when handling difficult, struggling prey, or when they have captured a fish that is being held precariously and might otherwise escape.

Although the basic physics of dipole fields predict the effect of this curling behavior, a number of experiments were conducted to directly measure the resulting electric field and its effect on prey Catania, c. Nor can an investigator chase a hunting eel with electrodes and hope to get useful data.

To measure the electric field within prey, the pithed fish preparation was again used. However, in this case, the fish was impaled on a custom-made, plastic electrode holder Figure 7C. The recording electrodes consisted of two wrappings of thin copper wire spaced 1 cm apart on the long projection of the T-shaped electrode holder.

The thin insulated leads from the electrodes led to a data acquisition unit that recorded the electrical potential. At the same time, the insulated leads provided a convenient handle—much like a fishing line—that could be manipulated by the investigator. Finally, the upper part of the T-shaped electrode holder prevented the eel from swallowing the preparation.

This condition likely mimics natural situations during which prey fish with defensive spines have been caught but are difficult to swallow. The preparation provided data from numerous eels, showing that the intensity of the electric field experienced by prey often more than doubled when the eel curled Figures 7F,G.

Recall, that electric eels cannot increase the magnitude of their total power output during the high-voltage volleys, rather every electrocyte is active during each high-voltage EOD see above. Therefore, the increase in measured field strength resulted from the reconfiguration of the electric field.

The electric field was concentrated, so-to-speak, through the prey item, much like focusing the fixed power of a flashlight into a smaller area. It might seem surprising that, in many cases, the field strength within prey more than doubled when the eel curled.

Therefore the negative pole with an effect that is added to the positive pole may have a greater effect, based on proximity, than the positive pole during the curling behavior. What benefit does this behavior provide the eel? Although it intensifies the electric field through prey, a large electric eel would seem to have enough power from just the positive pole.

This appeared to be the case when an eel was offered goldfish. Clearly, some prey are more resistive to electricity than others. Curling provides a mechanism for electrifying prey that are both physically and electrically, more resistive. The answer seems obvious in retrospect.

Figure 8. Frame captured from video showing an eel attacking a crayfish. This suggests that crayfish are more resistant to electric discharges from Catania, c , reproduced with permission. In the pithed-fish preparation, this was measured based on whole-body fish tension. Crayfish provide a different window into this effect because many of their paired muscles are asymmetric: the muscles that close their claws are more powerful than the muscles that open them.

As a result, the effect of repeated high-voltage volleys from the eel electrifying a crayfish was readily apparent. Unlike the situation in fish, where contraction of symmetric muscle groups resulted in total immobility, in crayfish it was possible to watch the claws open and close with repeated high voltage volleys see video in Catania, c. Indeed, the same procedure is used with a stimulator in muscle physiology labs to investigate fatigue.

To investigate this outcome a stimulator was first used to mimic the effects of an electric eel on prey muscle preparations Figures 9A—C. Muscle tension from a single stimulator pulse was first measured. This was followed by five bouts of electrical stimulation, each lasting half a second and consisting of 1 ms electrical pulses delivered at Hz. Half a second after the last stimulation bout, muscle tension was then measured again for a single stimulator pulse. In a pithed fish preparation, the muscle tension response had dropped drastically.

In a crayfish tail preparation, there was only a slight drop in muscle tension after five bouts of stimulation. However, after extending the number of stimulation bouts to 10 Figure 9D , tension responses in the crayfish tail responses had also dropped drastically. Finally, after a 30 s recovery period, the muscle preparations showed substantial recovery. Figure 9. Paradigm used to simulate the effect of eel volleys on prey muscles.

A Pithed fish attached to a force transducer and stimulator. B Example of whole fish tension responses to single stimulator pulses prior to blue arrows a series of ms, Hz volleys, and after red and black arrows volleys.

Note the dramatic reduction on contractile force following five volleys red arrow. C Crayfish tail preparation and stimulator. D Example of crayfish tail tension responses as described above. Note the difference in time scale, and that more volleys 10 were required to cause a similar reduction in contractile force. E An electric eel was induced to perform a curling attack on prey-electrode preparation. The recorded high-voltage EOD triggered an SD 9 grass stimulator connected to either a pithed fish preparation, or a crayfish tail preparation connected in turn to a force transducer.

Tension in each preparation dropped dramatically over time F,G and particularly quickly when subjected to the continuous high-frequency stimulation that co-occurs with curling from Catania, c , reproduced with permission. These experiments demonstrate the predictable, fatiguing effect of repeated bouts of high-frequency muscle stimulation.

The half-second, post-bout testing time for muscle fatigue was chosen because after electric eels engage in this form of behavior while curled, they then reposition the prey for swallowing within a half-second.

Thus they need only cause a short period of muscle inactivation to reposition and swallow helpless prey. To provide more data regarding the effect of eel curling behavior, an additional more elaborate experiment was designed. Thus this paradigm tested the effect of the actual, real-time rate of the high-voltage volley on the muscle preparations i.

As in the previously described paradigm, the repeated bouts of stimulation resulted in a rapid and drastic reduction in muscle contractile force. Finally, although this was not explicitly investigated for eels, the oral region of most animals is very sensitive. This would explain, for example, why eels sometimes electrify the crayfish, while in the curled position, for over a minute Catania, c.

This is far longer than previously observed for any other prey. By the end of such a bout, the crayfish limbs are invariably completely flaccid, and the eel can swallow its prey at leisure. To summarize these results, electric eels have a strategy for inactivating the muscles of difficult, struggling prey that have been grasped but not subdued. In these cases, the eels concentrate the electric field by sandwiching the prey between the two poles of their long electric organ.

This likely ensures activation of the motor neuron efferents in prey that might have more resistive skin or cutical or in the case of juvenile eels, prey might simply not be affected by the output of their weaker electric organ in a linear configuration. Once curled to amplify the local field through the prey, the eels give off repeated volleys. The resulting effect on prey muscles is remarkably similar to the application of a paralyzing agent, such as curare, that blocks the neuromuscular junction.

There is a precipitous drop in muscle function. In essence, the eels have a new method for inactivating muscles, through the induction of involuntary fatigue. The strategy is analogous to the use of paralyzing venom, but it takes effect more rapidly.

In March of , Alexander von Humboldt supposedly observed an extraordinary encounter between electric eels and horses. He had been traveling in South America and one of his goals was to experiment with electric eels.

Most histories of electric fish include an illustration and description of the event. But not everyone believed the story Catania, On the other hand, there was no obvious reason for anyone to investigate further. The story had little relevance to the biology of electric eels and it served as an amusing anecdote. In the course of many of the experimental investigations described above, electric eels were transferred from a home cage to an experimental cage.

Depending on the size of the eel, sometimes the net had a metal rim and handle. Although this may not seem wise, the investigator always wore rubber gloves, such that the composition of the handle was inconsequential or so it seemed.

On many occasions, when the metal net was brought toward a large eel, the eel transitioned from a retreat to an explosive attack targeting the metal part of the net. The eel rapidly approached, followed the metal rim to where it exited the water, and then leaped upward while pressing its lower jaw to the metal handle.

In coordination with the upward leap, the eel gave off long volleys of its high-voltage EOD. The behavior was particularly surprising because at no other time were electric eels observed leaping upward from the aquarium.

The behavior gave the impression of a formidable, electrical attack. This was accomplished using two flat metal plates attached to a plastic handle. The lower plate was submerged most of the way in the water, separated from the upper plate which was entirely above the water by a thin insulator. A voltmeter was then connected between the two plates.

When the eels attacked the apparatus, they emerged from the water pressing their lower jaw against the lower plate while giving off their high-voltage volleys. As they rose higher, they crossed from the lower plate to the upper plate, and thus variations in the electrical potential could be recorded as the eels ascended Figure Figure Measurement of voltage during eel leaping defense.

A Schematic of the plate arrangement and voltmeter used to measure the electrical potential as eels ascended the conductor.

Black line indicates a non-conductor separating the plates. B Frames from high-speed video for a shocking leap. C Voltage measured as the eel ascended. Numbers 1—3 correspond the plates illustrated in B , indicating the location of the eel at time of discharge. D The proposed equivalent circuit that develops as the eel emerges from the water. This path becomes more resistant as the eel ascends to greater heights from Catania, a , reproduced with permission.

As might be predicted, the electrical potential voltage increased dramatically as the eels ascended to greater heights. This is best appreciated by considering the equivalent circuit that is thought to develop Figure 10D. In this case, the resistances in the circuit include the internal resistance of the eel r and the resistance of the surrounding water Rw.

When the eel emerges from the water and presses its lower jaw against an object, the circuit changes such that a new resistance exists above the water. As the eel ascends to greater heights, the resistance of the return path along the eel increases, hence the measured voltage increases in proportion to height.

In other words, the higher the eel leaps, the less pleasant the experience for the target. Yet it was not entirely clear how similar the behavior described above might be to what Humboldt observed. He reported that the eels emerged from the mud and attacked, with at least some eels pressing themselves against the horses von Humboldt, But he did not describe eels as leaping out of the water.

Fishing with horses. A This illustration depicts the battle between eels and horses observed by Alexander von Humboldt in March of B Schematic and plates showing a fisherman being shocked by an electric eel Plate A is in the public domain, B from Catania, b , reproduced with permission. His original publication did not include an illustration of the events, but many subsequent authors provided their own illustrations. The most significant illustration seems to have been lesser known and the least circulated and re-published.

This particular image stands out for two reasons. First, it is by far the most accurate depiction of the events described by Humboldt. Humboldt described fishermen waving reeds, a fisherman that had climbed an overhanging tree above the pool, horses that had escaped, and horses that had collapsed on the nearby shoreline. All of these details are included in the image. The second reason for its significance is the author. Robert Schomburgk was a friend and admirer of Humboldt Schomburgk, Humboldt helped the Schomburgk brothers obtain funding for their own trip to South America Payne, and provided advice Roth, Moreover, the illustration shows an electric eel that has emerged from the water to press its lower jaw against one of the horses.

Figure 11B documents this event, which can be viewed from Hawkin Much can be inferred from the circumstances surrounding this incident. For example, the fisherman wades into a relatively shallow pool while attached to a rope, the other end of which is held by one of his comrades on shore. The fisherman also holds a machete, which is a common means of killing electric eels. The man searches for the eel, but the eel finds him first.

The predictable effect is instant paralysis from involuntary muscle activation, as previously described for prey. This possibility was obviously anticipated, as evidenced by the rope, which was used to immediately drag the incapacitated fisherman to shore. The man recovered quickly and the eel which pursued him to shore was then killed with a machete.

When an eel emerges from the water to make direct contact with a potential threat, the circuit that develops is comparatively simple.

It was, therefore, possible to investigate most of the variables in the circuit and to estimate how current would flow through different elements for these measurements and calculations, all values refer to the peak voltages and currents during the high-voltage EOD. The analysis begins with a determination of the EMF in volts and internal resistance r for each eel.

These variables are unique for any given eel at a particular stage of development. As the eel grows and adds electrocytes, its internal resistance and EMF change the former decreasing, and the latter increasing. Previous investigations of eels Brown, and other electric fish Bell et al. But a more accurate method is to add a variable resistor to the circuit and measure V and I during each high-voltage EOD as the resistance is varied.

When this is done, a plot of V vs. I yields a straight line with a slope equivalent to the negative of the internal resistance r. The details of the method are given in Catania a. Using this procedure Catania, a , b , the EMF and internal resistance r of five different electric eels of different sizes were recently measured.

Because these details may not interest all readers, they are omitted for brevity but can be reviewed in Catania a.

Figure 12 shows the EMF and internal resistance that were determined for five different eels. The circuit in Figure 12B shows the additional resistance of the return path from head to water Ro. This configuration is often called a voltage divider circuit, and it has many parallels with circuits used to modulate the amplitude of an electric output in a wide range of electrical equipment. Rather, each successive approximation of the behavior in an ancestor, starting with an approach to the threat in the water, and followed by direct contact, and then by emergence from the water to greater and greater heights all while giving off the high-voltage EOD , would provide a selective advantage for deterring a predator.

B Estimate resistances and the maximum resistance of the return path to the water during the leap by eel shown at the top in A ; from data in Catania, b. Arrow marks break in circuit as arm was withdrawn. Current increased as the eel ascended, as predicted from the equivalent circuit in B. Current peaks were approximately 43 milliamps. Resistances are shown in black, currents are shown in red plates from Catania, a , b ; Copyright K.

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