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The Eclectic Nature of Electric Fish: Lessons for Neuroscience and Beyond

By Dhruv Mehrotra

Electricity is an essential component of modern life that is oftentimes taken for granted. However, there used to be a time when human civilization did not know about the existence of electricity. In fact, the only organisms that were known to harness electricity were fish! In this article, we will learn about ways in which humans have harnessed the electric abilities of fish, current research into the ways in which fish utilize electricity, why they have become a popular model system in neuroscience and how they have inspired new technologies for the future. Some species of electric fish (e.g. the electric eel), are well-known due to their ability to discharge electricity up to hundreds of millivolts. The eels use electric discharges for various purposes such as self-defense and  incapacitating prey.

… there used to be a time when human civilization did not know about the existence of electricity. In fact, the only organisms that were known to harness electricity were fish!

In modern times, electricity is represented through our various electronic devices, lighting structures, and battery operated devices. Interestingly, the first battery made by Alessandro Volta was inspired by the design of the eel’s electric organs (Wu, 1984). In addition to their contribution to battery development, electric fish were also instrumental in medical treatment. The ancient Romans and Egyptians used eels to treat a variety of ailments ranging from pain to epilepsy. These fish were used to basically perform an ancient version of electroconvulsive therapy. Today, the usage of electricity to alleviate pain has given rise to a host of medical devices and therapies, notably transcutaneous electrical nerve stimulation (TENS) and cranial electrotherapy stimulation. Most TENS devices have been deemed safe enough for FDA clearance and are readily available and sold over-the-counter, including on Amazon for as low as $30 a unit.

Even today, electric eels remain an organism of interest within the research space. While we now understand how the electric eel uses this discharge, the broader impacts of such electrical discharges on other organisms in its environment remains unknown. It has been previously proposed that high voltage discharges, such as lightning, can drive gene transfer across organisms (Kotnik, 2013). This hypothesis was recently explored by a Japanese research group that used the eel’s electrical discharge to transfect DNA into embryos (Sakaki et al., 2023). Cell transfection is a routine procedure in modern laboratories in which foreign DNA is inserted into cells, typically for the purposes of conferring them with properties they do not have. Cell transfection is the backbone of medical interventions such as the production of human insulin by bacteria, as well as gene therapy. However, this report suggests that eels could mediate similar genetic manipulations in their natural habitats. If true, this can open further investigations into how eels exploit their electric discharge in natural settings. The pattern of eel discharges could be mimicked in modern electrical stimulation devices for alleviation of pain symptoms.

… electric fish were also instrumental in medical treatment. The ancient Romans and Egyptians used eels to treat a variety of ailments ranging from pain to epilepsy.

Another important component of electric fish is their ability to sense surroundings. Some fish have a typical discharge of less than one volt (e.g. less than an AA battery)! As a result, these discharges cannot be used for self-defense. In the dark, murky rivers of Africa (genera Mormyridae) and South America (genera Apteronotidae, Gymnotidae, Hypopomidae, among others) that these fish call home, their weak electric discharges endow them with the ability to sense their surrounding, known as electrolocation. Electrolocation helps them locate and find prey and shelter, as well as infer the shape, distance and electrical impedance of objects and individuals in their surroundings. Weakly electric fish also use electrolocation for communication, notably via courtship and aggression signals. In fact, a recent study (Pedraja & Sawtell, 2024), has shown that an electric fish can use the electrical discharge of other electric fish to extend its range of electrolocation! Interestingly, the electric eel can generate both strong and weak electric fields (Catania, 2019). It uses the strong fields to hunt and immobilize prey, and weak fields to find hidden prey. And like the electric eel, weakly electric fish have inspired the creation of new technology such as  underwater exploration devices that rely on electrical discharges to investigate shipwrecks and trenches (Solberg et al, 2007). 

The discovery of electrolocation in weakly electric fish made them a popular model for research in neuroscience. These fish have led to important insights in perception and neural coding of communication signals across species.

The discovery of electrolocation in weakly electric fish made them a popular model for research in neuroscience. These fish have led to important insights in perception and neural coding of communication signals across species. Weakly electric fish actively interact with the environment to understand their surroundings, like how bats use echolocation. Imagine if you were blindfolded and were told to identify an object – you would try feeling it from all sides. Based on what you felt, you might revise your assessment of the object’s identity. In this way, active sensing incorporates a constant feedback process. This process is easily studied in weakly electric fish. Researchers are able to detect and generate electrical signals and play these artificial signals back to the fish; which they respond to as if it were a natural signal. This makes the fish a tractable model system. For example, a study using electric fish showed that pauses during communication arise as a mechanism to allow the nervous system to recover from synaptic fatigue! (Kohashi et al, 2021). In addition, fish neural circuits are relatively simpler and easier to trace, enabling us to elucidate fundamental principles such as motor learning and plasticity, best exemplified by the jamming avoidance response and refuge tracking behaviors. 

To summarize, in this article, we learnt about the amazing ability of fish to harness electricity in various ways, and how this inspired humans to create new technologies that are indispensable today. The article also describes how they provide invaluable insights into neuroscience research. There is a lot more to learn about the behavior of these organisms, which may provide novel directions into neuroscience research and the development of novel therapeutic interventions.

 

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Written by Dhruv Mehrotra
Illustrated by Aishwaria Maxwell
Edited by Paige Nicklas, Gabrielle Sarlo, and Alvi Khan

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References

Catania, K. C. (2019). The astonishing behavior of electric eels. Frontiers in Integrative Neuroscience, 13(July), 1–18. https://doi.org/10.3389/fnint.2019.00023

Sakaki, S., Ito, R., Abe, H., Kinoshita, M., Hondo, E., & Iida, A. (2023). Electric organ discharge from electric eel facilitates DNA transformation into teleost larvae in laboratory conditions. PeerJ, 11, 1–13. https://doi.org/10.7717/peerj.16596

Kohashi, T., Lube, A.J., Yang, J.H., Roberts, Gaddipati, P.S., and Carlson, B.A. (2021). Pauses during communication release behavioral habituation through recovery from synaptic depression. Curr. Biol. 31, 3145–3152. https://doi.org/10.1016/j.cub.2021.04.056

Kotnik T. Lightning-triggered electroporation and electrofusion as possible contributors to natural horizontal gene transfer. Physics of Life Reviews. 2013 Sep;10(3):351-370. https://doi.org/10.1016/j.plrev.2013.05.001.

Pedraja, F., Sawtell, N.B. Collective sensing in electric fish. Nature 628, 139–144 (2024). https://doi.org/10.1038/s41586-024-07157-x

Solberg J.R., Lynch K. M., and MacIver M. A., “Robotic Electrolocation: Active Underwater Target Localization with Electric Fields,” Proceedings 2007 IEEE International Conference on Robotics and Automation, Rome, Italy, 2007, pp. 4879-4886, doi: 10.1109/ROBOT.2007.364231.

Wu, C. H. (1984). Electric fish and the discovery of animal electricity. American Scientist, 72(6), 598–607.

Author

  • Dhruv Mehrotra

    Dhruv is a PhD candidate at McGill University in Montreal, Canada. He uses computational tools to investigate brain dynamics in rodent electrophysiological data during sleep. His area of focus is the brain’s compass, also known as the head-direction system. He is passionate about mentorship and making science more accessible to the public. Outside work, he enjoys swimming, volleyball, and cooking.

Dhruv Mehrotra

Dhruv is a PhD candidate at McGill University in Montreal, Canada. He uses computational tools to investigate brain dynamics in rodent electrophysiological data during sleep. His area of focus is the brain’s compass, also known as the head-direction system. He is passionate about mentorship and making science more accessible to the public. Outside work, he enjoys swimming, volleyball, and cooking.

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