The Worst Thing About Tongue-Eating Isopods Is How They Breed

The parasite is shown in purple in this frankly unacceptably terrifying view. Kory Evans / Rice University

A biologist studying skull shape evolution in fish at Rice University, Texas, made a horrifying discovery while scanning what looked like an ordinary wrasse fish. Luckily he shared it on Twitter so we can all be grossed out. 

Kory Evans, assistant professor in the Department of BioSciences at Rice University, was digitizing X-ray scans of the fish, only to find that inside its mouth, where the tongue should be, was a parasitic isopod that had "effectively become the new tongue".

"Mondays aren't usually this eventful," Evans wrote on Twitter. "I found a tongue-eating isopod (purple) in one of our wrasse scans this morning while digitizing it."

Kory Evans / Rice University



These parasites are truly bizarre, and frankly need to be dealt with before we even think about moving onto Covid-19. Cymothoa exigua, aka the tongue-eating louse (let's call a spade a spade and terrifying nightmare louse a terrifying nightmare louse), enters an unsuspecting fish through the gills, where it hunkers down until it matures. 

So far, so grim. I don't have gills, but I imagine it's not the most comfortable thing to have someone enter through my breathing flaps. Interestingly, though, the parasites are protandrous hermaphrodites and enter the gills as males. After a short time, they can go on to either be male or functional females.

The males attach to the gill arches. The females, meanwhile, crawl out from the gills and get to work on becoming a tongue. Using their front claws, they sever the blood vessels in the fish's tongue and feast on the blood. With good nutrition from the fish's blood, the females grow until they are roughly tongue-sized, about 8-29 millimeters long and 4-14 millimeters wide. Which is perfect, as without blood flow, the tongue withers away and falls off. 

The females attach themselves to the tongue stub with hook-like pereopods (essentially legs) to become a pseudo-tongue. Here's one in action, but be warned, the horror show isn't over yet.

With little indication that there is reduced feeding or ability to respire by the host fish, researchers believe the louse effectively serves as a mechanical replacement for the fish's own tongue, though it's obviously there to steal bits of food for itself as the fish tries to feed. According to a 2012 study, it's the only known case in animals of a parasite that functionally replaces a host structure.

I know what you're thinking (you perverts), how do they mate? Well, of course, this takes place within the host fish. While the fish is tongue-less and doing whatever the fish equivalent of freaking out is, the parasites get freaky, most likely within the gills or inside the fish's mouth. The babies are released and go off in search of their own host, and the terrifying cycle starts all over again.

If you imagine this from the fish's perspective, it truly is horrifying. First, their tongue is gone, then it's back but you can't feel it and it's significantly more mobile than you remember, then suddenly something is having sex with it. 

Happy Thursday, everybody.


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