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There are some underwater electric beasties, in the sea. And, in a fantasy world... nature is always worse.

My thoughts and ponderances

So, let's say the mermaids do have rubber, for simplicity. Great... now how do they insulate themselves without suffocating their gills?

Could they build a Faraday cage around themselves, maybe...? That's tricky though, as wouldn't that require ferrous metal? And that rusts, until the invention of stainless steel.

I guess the Faraday cage will still work, even if it's rusty? Not sure if they could cover it with some non-insulative, yet waterproof material, so they don't have to go about wearing a rusty cage.

TLDR: I figure a mixture of a faraday cage and a rubber suit is a possibility. Could it work?

Feel free to name your own ideas of how mermaids could protect themselves from electricity.

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  • $\begingroup$ Where would they even get the rubber from? Humans make rubber from the latex sap of certain land plants. The thing is these are all angiosperm plants, which only grow on land. Most of the groups we harvest rubber from don't have aquatic representatives, and seaweeds don't produce latex. It would be like trying to milk a fish. I know people have been experimenting with biomaterials derived from seaweed but I don't know if they're also insulators. $\endgroup$
    – user2352714
    Jan 2, 2021 at 7:12
  • $\begingroup$ Staying well away from live sources seems obvious. Without direct contact with a live source, there is no path through ground that would benefit by passing through the mermaid $\endgroup$
    – nzaman
    Jan 2, 2021 at 8:18
  • $\begingroup$ @user2352714 I mentioned it for simplicity. If actual rubber was not available, would a substitute exist? I could work out some way for them to get rubber, if necessary. $\endgroup$
    – Johnny
    Jan 2, 2021 at 8:24
  • $\begingroup$ @Johnny I'm not sure. There's been a lot of work on creating bioplastics out of algae (can't post the links because they are too long for a comment) but they don't say anything about how good of an insulator they are because their creators weren't focused on the electrical applications. There's probably some natural material that can be used as an insulator in the ocean. $\endgroup$
    – user2352714
    Jan 2, 2021 at 19:44

2 Answers 2

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Sea water, with its saline content, is a good conductor. If the merpeople can insulate themselves from the water, they are relatively safe, as the electricity will prefer the path of least resistance given in this case by water.

Therefore your merpeople just need to secrete an oily mucus covering their bodies, which will keep them physically separated from the salty water.

A rusty Faraday cage won't work, because rust is not a conductor, and Faraday cages trap the electric field only when made by conductors.

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  • $\begingroup$ Adding to this, this is why electrofishing doesn't work in salt water. what-if.xkcd.com/156 Most fish that use electric signals are freshwater. Torpedo rays aren't but I don't know how they get around the salinity issue. $\endgroup$
    – user2352714
    Jan 1, 2021 at 19:33
  • $\begingroup$ Would a Faraday CAGE still work underwater being penetrated by the sea water, another conductor? $\endgroup$
    – DKNguyen
    Jan 2, 2021 at 2:18
  • $\begingroup$ Dutch: Neat idea with the mucus. Not sure if it would work, though, as fish already produce mucus, and they seem quite vulnerable to electricity. Unless they could get it to a suitable thickness, and a material like olive oil, which is a surprisingly good insulator. @DKNguyen So long as the Faraday cage was tight enough and more conductive than the sea water. $\endgroup$
    – Johnny
    Jan 2, 2021 at 8:25
  • $\begingroup$ @Johnny This sounds like it calls for...live experiments...but where to get a cheap saltwater fish and how to safely get it inside an perforated aluminum box $\endgroup$
    – DKNguyen
    Jan 2, 2021 at 20:07
  • $\begingroup$ @user2352714 According to wikipedia, freshwater electric fish use high voltage electricity, and saltwater electric fish use low voltage high current electricity. $\endgroup$
    – JanKanis
    Jan 4, 2021 at 16:43
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So I looked into it a bit, and I was being silly. You only need iron for a Faraday cage if you want to stop radiowaves, copper works fine for electricity, since it's far more conductive than saltwater. So there's no need to cover iron with water-proof layers (since as mentioned, iron covered in rust loses its effect).

With mucus, it's a neat idea. But, fish already do that, and it doesn't seem to be adequate protection against electricity.

So, I figure you can just give them rubber suits, with slits for the gills, and copper Faraday cages covering the gill slits and face opening.

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  • $\begingroup$ I guess regular fish mucus either doesn't insulate enough or doesn't cover the fish entirely (e.g. the gills). Having individual faraday cages covering gills won't work. The cage needs to be able to conduct the electricity around what it is protecting, so you'll need to have a faraday cage covering at least the whole mouth/gills part. Multiple separate cages won't work. I guess sticking the fully mucus-isolated tail out of the cage is ok, though I'm not entirely sure. $\endgroup$
    – JanKanis
    Jan 4, 2021 at 16:39
  • $\begingroup$ @JanKanis Yes, the idea was cages covering the face and gill slits. They should pick up the current, and redirect it into the water. It can't go through the rubber suit the cage is connected to, and I don't see why it would jump through the Faraday cage into the gills. $\endgroup$
    – Johnny
    Jan 4, 2021 at 21:20

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