As It Happens

Behold the parasite that eats — and then becomes — a fish's tongue

Kory Evans was digitizing scans of fish one morning like he always does when he came across a wrasse with what appeared to be a big, ugly bug in its mouth. But on closer inspection, it turned out to be a parasitic isopod known as a tongue-eating louse.

Scientist Kory Evans found tongue-eating louse inside the mouth of a wrasse

Scientist Kory Evans found a tongue-eating louse inside the mouth of a wrasse while looking through scans of fish skeletons one morning. (Submitted by Kory Evans)

Transcript

Kory Evans was digitizing scans of fish skeletons one morning like he always does when he came across a wrasse with what appeared to be a big, ugly bug in its mouth.

Evans is an evolutionary biologist at Rice University in Texas who studies fish skulls — and it's not unusual for a fish's last snack to show up in one of his scans. 

"That's always a fun surprise in and of itself — but this was weird because the fish I was looking at was actually a vegetarian," he told As It Happens guest host Helen Mann.

"I hadn't had coffee. I was like, 'What did you eat?' And I'm staring at it and I'm looking at the thing head on, and then it's like 30 seconds and I realize exactly what it was. I was like, 'Oh, gross.'"

This was no fish food. It was a parasitic isopod known as a tongue-eating louse.

The tongue-eating louse enters a fish's mouth through its gills, latches onto its tongue, and severs the blood vessels. Then it feeds off that blood until the tongue withers and falls off. (Submitted by Kory Evans)

The crustacean enters a fish's mouth through its gills, latches onto its tongue, and severs the blood vessels. Then it feeds off that blood until the tongue withers and falls off.

After that, the louse basically becomes the fish's new tongue, siphoning off nutrients as it eats. It's a grisly fate for the fish, Evans said — but not necessarily a fatal one.  

"So far, what we've learned is that as long as it's just a single isopod on the tongue, the fish actually do just fine," he said.

"They do lose their tongue. So that's less great. Other than that, they seem to do all right."

Evans studies evolutionary traits in fish. He's currently working on a project that involves scanning hundreds of species of wrasse and creating three-dimensional models of their skeletons to get a better sense of how and why their skulls take certain shapes. 

He documents his work on Twitter with the hashtag #BackDatWrasseUp. And when he shared his parasitic discovery, he garnered a lot of attention — from regular people and fish science enthusiasts, alike.

Kory Evans is an evolutionary biologist at Rice University in Houston, Texas. (Submitted by Kory Evans)

"The response was way more than I expected. I just tweeted this so that my fish friends could see it. And it kind of took off," he said.

One of his followers, a Twitter user named Michael Morehead, even used his scans to make a virtual-reality walkthrough of the wrasse skull, louse and all. 

Evans has also piqued the interest of his fellow scientists. While tongue-eating louse aren't rare, they are understudied. And it's a bit unusual for one to show up in a vegetarian fish, he said. 

"For me right now, it's more of a gross surprise. But I have had a lot of people contacting me about potential collaborations," he said.

"So it might further my research in a completely unexpected direction. I did not think that I would ever be working on tongue-eating parasites."


Written by Sheena Goodyear. Interview produced by Menaka Raman-Wilms.

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