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First person: Behind a scientist's discovery of a tongue-replacing parasite

The famous tongue replacement isopod, Ceratothoa famosa, in the mouth of a Cape seabream.
The famous tongue replacement isopod, Ceratothoa famosa, in the mouth of a Cape seabream.

Professor Nico Smit specializes in aquatic parasitology at Northwestern University in South Africa. Many years ago, while working on his Ph.D., Smit ran across something special in the coastal waters off South Africa: a tongue-replacing parasite.


NICO SMIT: We found a new species of tongue replacement isopod. So these are the isopods that go into the mouth of the fish. They can sit on the tongue, then they destroy the tongue of the fish, and then they function as the fish’s tongue. And this is pretty amazing because it’s only known in the world where a parasite actually replaces the functional body part of an animal and then function as that body part.

CHAKRABARTI: I have to say my first response when seeing a photograph of this parasite was, Wow. Because it looks just like the fish’s tongue, but with some eyes staring out of his mouth. Now, Nico Smit says that the fish and parasite can live together for many, many years, decades, even because the fish can’t actually get rid of the parasite even if it wanted to.

SMIT: The amazing thing about this is that the fish doesn’t really then have a choice, because the parasite function as the tongue. So it needs the parasite to continue to be able to eat and all those kinds of things. But the parasite can’t stop feeding on the fish. It actually just takes some of the food of the fish. So in that sense the fish is fine and the parasite is fine. The fish needs to look after the parasite because if the parasite disappear, then the fish don’t have a tongue anymore and then the fish is in trouble.

CHAKRABARTI: So Professor Smit remembers that day, many years ago, when he first saw what would become a new species or a new species to science, I should say, of parasitic isopod.

SMIT: So I opened the mouth of the fish and there was this parasite just sitting there on the tongue. So I just thought … this is something really incredible. I don’t know if anyone is able to take a photo like that before. So I just took a took a photo and I didn’t really think about it.

I didn’t think about lighting or position or anything. It was just like, oh, my word. This is just incredible. It just so happened that at that moment I had just bought myself a small digital camera just to see, what is this thing about this digital camera? I wasn’t convinced it can take better photos.

… And we were at the coast. And I didn’t want to take my camera down to the rocks. So I had that small digital one with me and I took the photo with that. And then we went back to my university, and they were looking for photos to put on the website of the university, this department.

And I said, Why don’t you just use this photo? I tweet that photo and it went viral and it just went everywhere. And I took the photo and now I think it’s almost 15 years ago, 16 years ago. And it’s still one of the most used photos for illustrating this specific parasite behavior.

And then we actually named the specie after I took that photo and after the photo went viral. So we called this specie famosa because the parasite became famous even before it had the name. So then since then I realized, you know what? People are interested in this. A lot of the comments on the photos are, Eek! And you know, this is disgusting. Please remove it. We don’t want to see it. But in general, the comments are people [amazed] something like that exist. So that made me realize that there’s a hidden diversity of these actually stunning organisms that people would be interested in.

But they don’t see them because there’s not really a lot of photographs of those kinds of things available. … We as scientists are privileged enough to see these images and get a different idea of parasites when we see them like that. And so that’s what I tried to do with photography, especially of life glass, parasites.

Maybe if we see them in the light, if it was a good photo and a good story behind it, then we might just start to change our minds towards, you know, about not all parasites are bad and then maybe a good batch of them need conservation and then that’s it. That is part of our natural heritage that we should look after and not just ignore them.

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