Weird Parasite: Tongue-eating isopod that targets a fish by infiltrating its gills and latching onto its tongue

In the Gulf of California exists a living creature known as Cymothoa exigua, a tongue-eating isopod that targets a fish by infiltrating its gills and latching onto its tongue. The aim is not only to eat the tongue but eventually to replace the organ with its own body giving the fish with a new fully functioning tongue.


A Cymothoa exigua tongue-eating isopod that has consumed and replaced the tongue of a snapper, who is not wide-eyed because of terror. That’s just how fish normally look. Photo copyright Matthew R. Gilligan

According to Marine Biologist Rick Brusca of the University of Arizona, though this isopod targets several other fish, only with the rose snapper does it completely consume and replace the organ as an operating structure. He stresses that only this type of isopod can actually truly assume the functions of the organ.

In this case, Cymothoa exigua slowly drains the life out of the snapper’s tongue, which atrophies from the tip on back, bit by bit, until nothing but the muscular stub remains. The isopod now grasps with her rearmost three or four pairs of legs, essentially becoming the fish’s new tongue. And the isopod has likely evolved like this to keep her host alive, according to Brusca, allowing her more time to rear her young.


A closely related Ceratothoa italica isopod, which unlike Cymothoa exigua does not functionally replace its host’s tongue, perhaps out of laziness. Photo: Maria Sala/University College Dublin

But once the tongue is gone, the female is left without a food supply. So as her young continue to develop, she lives solely on stored energy supplies, according to Brusca. Scientists aren’t yet sure at what point the young are released, or how exactly they find fish of their own, but Brusca reckons that the female may wait until her host is schooling with other fish to cut her offspring loose from the brood pouch, giving the young plenty of targets.

Like many victims of parasites, the poor snapper gets nothing but misery and premature death.

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