Ichthyothropy | E. Christopher Clark


Ichthyothropy is a physiological condition in which the legs of a human or humanoid being are transformed into the tail of a fish. Afflicted individuals call themselves Merfolk.

Transmission & Vectors

The primary cause of the malady is the bite of a marine animal which has swum too deep in the The Waters of the River Without End, though the kiss of a Merfolk also does the trick.


But whether the carrier is a mermaid or a manatee, they ultimately infect other individuals in the same way: through a pathogen in their saliva or mouth-based mucus.


When the pathogen is introduced directly into the bloodstream, as in a bite, the resulting condition is nearly instantaneous and entirely irreversible. When a Merfolk’s kiss is the cause, the resulting saliva-to-saliva transmission allows the body of the newly infected individual more time to adjust. This results in a version of the condition that is controllable by the subject.


The primary symptom of the condition is the merging of the infected individual’s legs into a fish-like tail, with the characteristics of the tail—markings, coloration, etc.—inherited from the carrier who infected the individual.


Secondary symptoms are the development of gills on the back of the individual, the ability to breathe underwater for prolonged periods, and the ability to hide (and therefore protect) their genitalia within the confines of their tails.


The condition, for better or worse, renders merfolk sterile. So anything they choose to do with their genitals is purely for pleasure, not procreation. The only way to make more merfolk is with a bite or a kiss.


The condition is untreatable in individuals infected through the bite of a marine animal. Individuals infected through a merfolk’s kiss may reverse the condition at will by removing themselves from water. But full submersion in water, whether intended or not, will transform them right back. So merfolk must proceed with caution when taking a swim—or a bath!

Cultural Reception

Merfolk appear in the folklore of many Earthling cultures, but the cultural reception of the condition varies. Much of Western society, influenced by a later interpretation of the Sirens of Greek mythology, have long viewed merfolk—mermaids, in particular—as nothing but a pack of ne’er-do-wells who delight in the seduction and destruction of sea-faring peoples.


Other cultures view those with the condition as mostly benevolent figures charged with the protection of bodies of water. Elven societies typically venerate Merfolk for their close connection to nature. Dwarves see them as shrewd but fair guardians of underwater resources. But Kíndallans view victims of ichthyothropy as lesser beings, given that they’ve been robbed of their ability to shape-shift into any other form.

Chronic, Acquired
Affected Species


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Dec 29, 2020 15:19 by Dr Emily Vair-Turnbull

This is a really cool interpretation of merfolk. I like the idea that it's transmitted through a bite or a kiss, and that, depending on the vector of transmission, it behaves in different ways.

Dec 29, 2020 16:56 by E. Christopher Clark

Thanks! Originally I was going to try and write them as an alien species (similar to what I did with elves and dwarves), but then I realized there was little reason for them to end up looking like the mermaids my daughter thinks of when she thinks of mermaids, so I went back to the drawing board.

Now it's time for the awkward wave.
Jan 26, 2023 13:51

I love this interpretation of merfolks as the result of a manatee-transmitted disease! That transition from land-dweller to merfolk must be painful, especially the initial merging of the legs.

With love,   Pouaseuille.
Jan 26, 2023 17:59 by E. Christopher Clark

Thanks so much for reading it! Yes, I definitely imagine that transition as pretty painful—which may explain why some merfolk are on the more bitter and vengeful side.

Now it's time for the awkward wave.
Jan 26, 2023 21:02 by Chris L

The fact that your mermaids are were-manatees makes my heart happy! Also genital-hiding for the... win??

Learn about the World of Wizard's Peak and check out my award winning article about the Ghost Boy of Kirinal!

Jan 27, 2023 11:53 by E. Christopher Clark

Well, I didn't mean to imply that they were *all* were-manatees, but I'm loving that my choice of manatee is giving folks a smile. Really, it's meant to be *any* marine animal that can pass things on, which is meant to explain how you could get both an Ariel (fish tail) and an Ursula (octopus bottom).

Now it's time for the awkward wave.
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