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Stunning and stealthy

The amazing electric eel

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©depositphotos.com/Yourth2007electric-eel

The electric eel (Electrophorus electricus) lurks in the murky waters of the swamps and rivers of northern South America. With its highly sophisticated system of electrolocation, it is a stealthy predator, having the ability to navigate and hunt in conditions of low visibility. Using ‘electroreceptors’ to detect distortions in an electric field generated within its own body, it can locate a potential meal undetected. It then immobilizes its prey using a powerful electric shock, sizeable enough to stun a large mammal such as a horse, or even kill a man.1 Having a long cylindrical body it closely resembles what we commonly understand by eels (order Anguilliformes); however it belongs to a different fish order (Gymnotiformes).

Fish that can detect electric fields are called electroreceptive and those that can generate strong electric fields like these eels are called electrogenic.

How does the electric eel generate such high voltages?

Electric fish are not alone in generating electricity. In fact all living organisms do this to some degree. The muscles in our own bodies, for example, are controlled by the brain using electric signals. Electrons produced by bacteria can be used to generate electricity in a fuel cell.2 Electric eels produce electricity in the same way as muscles, using energy from food to charge cells called electrocytes (see box below). Although each cell carries only a small charge, by stacking up thousands of these in series, like batteries in a torch, as much as 650 volts (V) can be generated. Arranging many stacks in parallel results in a current of around 1 ampere (A), providing a shock of around 650 watts (W; 1 W = 1 V × 1 A).3

How do electric eels not electrocute themselves?

CC-BY-SA Steven Walling via Wikipediaeel

Scientists are not entirely sure of the answer to this question, but there are some interesting observations that may shed light on the matter. Firstly, the electric eel’s vital organs (such as the brain and heart) are located near the head, away from the electricity-producing organs, and are surrounded by fatty tissue which could act as an insulator. The skin also appears to have insulating properties, as eels with damaged skin have been observed to be more vulnerable to their own electric shocks.

Secondly, electric eels produce some of their most powerful shocks when mating—but without harming the mate. However, if these voltage bursts are emitted when not mating, they can kill the other eel.4 This suggests that they have a protection system that can be switched on.

Could the electric eel have evolved?

It is difficult to imagine how this could have happened through small steps, as the Darwinian process requires. Unless the shock generated was significant from the start, rather than stunning the prey it would have just alerted it to the presence of danger. Moreover, in order to evolve the ability to stun, electric eels must have simultaneously evolved a self protection system. Every time a mutation arose which increased the shock voltage, another mutation would have been required to improve the eel’s electrical insulation—and it would seem unlikely that just one mutation would have been sufficient. Moving organs closer to the head, for example, would likely require a number of mutations to arise together.

Although few fish are able to shock their prey, there are many species that use low voltage electric fields for navigation and communication. Electric eels are members of a group of South American fish, known as ‘knifefish’, all of which have the ability to electrolocate.5 African ‘elephantfish’ (family Mormyridae), are also capable of electrolocation and are said to have evolved this ability alongside their South American cousins. In fact, evolutionists have to argue that electric organs in fish evolved independently eight times.6 Given their complexity, it would seem remarkable, to say the least, that these systems could have evolved once, let alone eight times.

Both the knifefish of South America and the elephantfish of Africa use their electric organs for location and communication, and both use a number of different types of electroreceptors. Both groups also have species producing electric fields with a number of different, complex waveforms.7 Two species of knifefish, Brachyhypopomus bennetti and Brachyhypopomus walteri, are so similar that they might be thought to be the same species, except that the former produces a DC current and the latter an AC current.8,9 The evolution story, however, becomes even more remarkable as we delve deeper. To avoid their electrolocation apparatuses interfering with one another and jamming, some species employ a system whereby each fish changes the frequency of its electric discharge. Significantly, the way this works (the computational algorithm used) is virtually the same in the glass knifefish of South America (Eigenmannia) and the frankfish of Africa (Gymnarchus).10 Could the same jamming avoidance system have evolved independently in two different groups living on separate continents?

A masterpiece of design

The electric eel’s power plant eclipses anything produced by man, being compact, flexible, portable, eco-friendly and self-repairing. All its parts are perfectly integrated into a sleek body which enables the eel to swim with both speed and great agility. From the tiny cells that generate the electricity to the sophisticated software that analyzes distortions in the eel’s self-generated electric fields, it is a tribute to an awesome Creator.

electric-eel-anatomy
Electric eel anatomy.
Most of the electric eel is made up of electric organs. The Main organ and Hunter’s organ are responsible for producing and storing the strong electric charge. Sachs’ organ produces the low voltage electric field used for electrolocation.

How do electric eels generate electricity? (semi-technical)

Electric fish generate electricity in a similar way to nerves and muscles in our own bodies. Inside the electrocyte cells, special enzyme proteins called Na-K ATPase pump sodium ions out through the cell membrane and potassium ions in. (‘Na’ is the chemical symbol for sodium and ‘K’ the chemical symbol for potassium. ‘ATP’ stands for Adenosine triphosphate, the energy molecule11 used to drive the pump.) The imbalance of potassium ions inside and outside gives rise to a chemical gradient which acts so as to drive potassium ions back out of the cell. Similarly the imbalance of sodium ions gives rise to a chemical gradient which acts so as to drive sodium ions back into the cell. Other proteins embedded in the membrane act as potassium ion channels, pores which allow the potassium ions to leave the cell. As the positively charged potassium ions accumulate outside the cell, an electrical gradient arises across the cell membrane, with the outside of the cell more positively charged than the inside. The Na-K ATPase pumps are designed so that they select only positive ions as, otherwise, negative ions would also flow and neutralize the charge.

The chemical gradient acts so as to push potassium ions out and the electrical gradient acts to pull them back in. At the point of equilibrium, where the chemical and electrical forces cancel one another out, the outside of the cell will be around 70 millivolts more positive than the inside. Hence, relatively speaking, the inside of the cell is negatively charged to −70 millivolts.

Na-K-ATPase-pump
The Na-K ATPase pump.
Two potassium ions (K+) enter the cell and three sodium ions (Na+) exit every cycle. The process is driven by energy from ATP molecules.

Yet more proteins embedded in the cell membrane provide sodium ion channels, pores which allow sodium ions to re-enter the cell. Normally these are closed but, when the electric organs are activated, they are opened and the positively charged sodium ions re-enter the cell, driven by the chemical gradient. In this case, equilibrium is reached at the point where the inside of the cell is positively charged to around 60 millivolts. The total voltage change is −70 to +60 millivolts, which is 130 mV or 0.13 V. This discharge occurs very rapidly, in around 1 millisecond. Since around 5,000 electrocytes are stacked up in series, by discharging all the cells simultaneously, around 5,000 × 0.13 V = 650 volts can be generated.

Glossary

Ion

An atom or molecule which carries an electric charge because it has an unequal number of electrons and protons. This will be negative if it has more electrons than protons, and positive if more protons than electrons. Both potassium (K+) and sodium (Na+) ions are positively charged.

Gradient

A change in the magnitude of something when moving from one point to another. For example, as you move away from an open fire, the temperature gets cooler. So the fire is generating a temperature gradient decreasing with distance.

Electrical gradient

A gradient involving the magnitude of electrical charge. E.g., if there are a greater number of positively charged ions outside a cell than inside, there will be an electrical gradient across the cell membrane. Due to like charges repelling one another, there will be a tendency for the ions to move so as to equalize the charge inside and outside. Ion movements due to an electrical gradient occur passively, driven by electrical potential energy, rather than actively, driven by energy derived from an external source such as an ATP molecule.

Chemical gradient

A gradient involving chemical concentration. E.g., if there are a greater number of sodium ions outside the cell than inside, there will be a sodium ion chemical gradient across the cell membrane. Due to the random movements of ions and constant collisions between them, there will be a tendency for the sodium ions to move from a high concentration to low concentration until equilibrium is reached, i.e. until there are the same number of sodium ions either side of the membrane.12 Again, this occurs passively, by diffusion. The movements are driven by the kinetic energy of the ions, rather than from energy derived from an external source such as an ATP molecule.

References and notes

  1. Piper, R., Extraordinary Animals: An Encyclopedia of Curious and Unusual Animals, pp. 40–42, Greenwood Press, USA, 2007. Return to text.
  2. Fuel cell that uses bacteria to generate electricity, Science News, 7 January 2008; sciencedaily.com. Return to text.
  3. Power [watts] = potential difference [volts] × current [amps]. Return to text.
  4. Electric Eel, Cleveland Metroparks Resource Library; resourcelibrary.clemetzoo.com/animals/164. Last accessed July 2013. Return to text.
  5. See e.g. our article on the black ghost knifefish, Creation 15(4):10–11, 1993; creation.com/knifefish. Return to text.
  6. Alves-Gomes, J.A., The evolution of electroreception and bioelectrogenesis in teleost fish: a phylogenetic perspective, Journal of Fish Biology 58(6):1489–1511, June 2001. Return to text.
  7. Hopkins, C.D., Convergent designs for electrogenesis and electroreception, Current Opinion in Neurobiology 5:769–777, 1995. Return to text.
  8. Sullivan, J.P. et al., Two new species and a new subgenus of toothed Brachyhypopomus electric knifefishes (Gymnotiformes, Hypopomidae) from the central Amazon and considerations pertaining to the evolution of a monophasic electric organ discharge, Zookeys 327:1-34, 2013. Return to text.
  9. Science News, AC or DC? Two newly described electric fish from the Amazon are wired differently, 28 August 2013; sciencedaily.com. Return to text.
  10. Hopkins, ref. 7, p. 775. Return to text.
  11. Thomas, B., ATP synthase: majestic molecular machine made by a mastermind, Creation 31(4):21–23, October 2009; creation.com/atp-synthase. Return to text.
  12. See Wieland, C., World Winding Down: A layman’s guide to the Second Law of Thermodynamics, Creation Book Publishers, Powder Springs, GA, 2013. Return to text.

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Readers’ comments

Maureen A.
I love Gavin B's comment. So much common sense and so much humour.
S. S.
I agree that the electric eel is yet another amazing marvel of our world. However, I wonder how it fits within the creationist framework. Yes, it appears to have incredible design, but it is designed to kill its prey. Did God create it like that originally? If not, how did it develop an ability to shock its prey?
Dominic Statham
Many creatures have equipment that seems designed for attacking, hurting, trapping, killing, or eating others, or defending themselves against such things—for example, the poison-injecting fangs of snakes, the great meat-eating cats, and the spider’s web, to name just a few. So when and how did these things, which are suited to a fallen world but were unnecessary before the Fall, come to be?

We answer these kind of questions in ch. 6 of the Creation Answers Book. You can read the chapter online here:

http://creation.com/images/pdfs/cabook/chapter6.pdf
Gavin B.
Sam M says, "the earlier stages of the electric eel would not have paralyzed their prey, but would they have simply confused it?" Yet Dominic already argued that they had to produce protective mechanisms at the same time as they developed their deadly electric generation ability, to protect them from paralyzing themselves. So if they were only able to confuse their prey, this doesn't resolve the issue of having to develop a protective mechanism at the same time, or they would have confused themselves. Then you would have a confused eel and a confused fish at the same time. I doubt whether a confused eel could catch a confused fish.
Reed C.
A very well written article Dominic. I have to say I love the way you refute the Darwinist commentators. It is another great reminder for all, that Darwinism is not based on science but is a lot of storytelling made to sound factual.
R. M.
Mr. Statham says that “… evolutionists have to argue that electric organs in fish evolved independently eight times. Given their complexity, it would seem remarkable, to say the least, that these systems could have evolved once, let alone eight times…”

In response, I offer the following comment. Physiological, anatomical, and phylogenetic studies have established that the electroplax organs of fishes are derived from “stacks” of motor end-plates in the myomeres of the trunk muscles of fishes. Given that this is an anatomical arrangement common to all fishes, it is not at all surprising that this basic structural arrangement has been elaborated into similar sorts of electrical organs a number of times in species that are only distantly related. The myoneural junctions of the serially-arranged myomeres of non-electric fishes contain all of the molecular and anatomical precursors of the electric organs. So each independent derivation did not have to “start from scratch” – most of the components were already available.
Dominic Statham
And how did their ability to sense and interpret the distortions in the electric fields evolve? And why do we find such similarities in the systems used for location and communication in fish living on different continents?

In his book, Not by Chance, Lee Spetner demonstrates, using fairly simple mathematics, the impossibility of random mutations and natural selection giving rise to convergent evolution.
Sam M.
Looking over this article, there are a few things that seem worth considering.

Having a protection system develop at the same rate the electrical discharge does is not unreasonable. In the case of some offspring being born who had too much voltage, or too little protection, they would be less likely to live, and as such be naturally selected whereas those with a proper balance had a higher likelihood to survive.

There is an answer to how this could have developed in small steps as well. As already mentioned in the article, "there are many species that use low voltage electric fields for navigation and communication". This being the case, consider this: The earlier stages of the electric eel would not have paralyzed their prey, but would they have simply confused it? If the eel is hunting prey that is used to using it's own electrical field to help navigate, and the eels minor charge is enough to throw that off, that could be enough of a benefit the allow the eel to catch prey more often compared to the eels whose charge did not effect the navigation of their prey. It's a very small benefit, of course, but small benefits lead to large changes when given millions of years. If their environment is as such that having the ability to give an electrical discharge, regardless of how small, benefits the species, then one would expect that this would carry on for future generations. As this continued, those who were born with gradually stronger voltages, therefore having a somewhat greater effect on prey, would again be more likely to catch prey, defend themselves, and breed.

Remember that there are ways to look at any one species and see rational ways that they could have evolved over time.
Dominic Statham
Your arguments are typical of the story telling evolutionists employ in support of their faith—and story telling is not science.

You wrote, "Having a protection system develop at the same rate the electrical discharge does is not unreasonable." Has anyone calculated the probability of this happening? I have little doubt that nobody has, in which case it cannot be argued that science has shown such a series of changes to be plausible.

How do you know that a weak electric field would confuse prey? Have you ever done an experiment to demonstrate this? Has anyone shown that fish producing weak electric fields for location or communication confuse other nearby fish making them easier to catch?

Professor Philip Skell, known as 'the father of carbene chemistry' remarked, "Darwinian explanations for such things are often too supple: Natural selection makes humans self-centered and aggressive—except when it makes them altruistic and peaceable. Or natural selection produces virile men who eagerly spread their seed—except when it prefers men who are faithful protectors and providers. When an explanation is so supple that it can explain any behavior, it is difficult to test it experimentally, much less use it as a catalyst for scientific discovery." See here.
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David M.
It's also worth mentioning that if all the electrolyte cells don't fire at exactly the same moment, the electric eel isn't so electric anymore. Discharging .13v into the water down the length of your body like dominos, isn't exactly a terrifying display of raw power.

It takes time for the "fire" signal, from the brain, to get to get to the cells in the tail. Which is exactly why the nerve paths running to the electrolyte cells near it's head are much much longer than those toward the tail. Each cell has the EXACT length of nerve path required so that it will get the "fire" signal from the brain not a moment sooner or later than any of the other cells.

This also seems a miraculous feat for evolution.

J. C.
I love your work, Dominic!
Bob S.
Thank you for your upbeat articles that are easy to understand. I notice that you put in a glossary. Nice touch!

Since God reveals Himself to unbelievers through the Creation and to believers through the Creation and the means defined in Scripture, the unbelievers must resort to stories and assumptions as the basis for what they call "evidence." Secularists have known, for thousands of years, that all of their thoughts must be based on either infinite regression, circular reasoning, or arbitrary, bare assertions.
Alan S.
If there is just one species that can be shown as impossible to have been achieved by evolution it must throw doubt upon the whole evolutionary hypothesis. Could the electric eel be one?
Dominic Statham
I would argue that this is true of every species!

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