Meet the Cymothoa Exigua: A Sex-Changing, Tongue-Eating Parasite

The world is full of parasites, and there are a lot out there that we can’t see or ones that we haven’t even discovered yet. There’s one tiny parasite that will probably give you nightmares if you give it a chance. Meet the Cymothoa exigua, a louse that likes to eat tongues. Cymothoa exigua is an isopod. It’s a fish parasite that only grows to about an inch long, even shorter if they’re males. This parasite is capable of replacing its host species’ entire organ. Since this is a tongue-eating fish parasite, you can easily surmise which organ it replaces—the fish tongue. This parasite can be seen primarily on snapper tongues, but it has been known to pester at least 7 other fish species. These parasites are also known as protandric hermaphrodites. These organisms literally undergo a sex change throughout their lives, starting out as males and switching to the female sex later on.

How they invade

The Cymothoa exigua enters a fish’s body through its gills. They will secure themselves and stay in that area until they have matured enough to develop their tongues. Once this has happened, the sex change occurs. All the males will then become females during at which time, the parasites detach themselves form the gills and slowly make their way to the tongue base—their chosen home for the rest of their lives.

The tongue base is the chosen permanent location for this parasite. It attaches itself to the fish’s tongue by piercing it with an extremely powerful bite. The incision made from this bite will be where louse will get its fill of blood. It will start sucking blood until it gets as much as it can, but will eventually keep drinking until all the blood from the fish’s tongue has been depleted. The end result is a bloodless, atrophied tongue that will eventually wither away and fall off.

However, the parasite will somehow stay in place, completely replacing the fish tongue with its own body. As horrifying as this may sound, this invasive process will not ever kill the host fish. It becomes a nuisance, but most fish manage even with such a large parasite in its mouth. The fish may not survive as well as it would without the parasite, but it will thrive regardless. The parasite will continue to feed off of the fish through mucus and blood that’s around its area.


Even if a fish has already accepted the fact that there’s a parasite in its mouth, it’ll still have to contend with reproduction. If there were still any unchanged males left in the gill chamber, it will climb into the area where the female louse is and mate with the female while it’s there attached as the fish tongue. If that’s not bad enough, the female will eventually give birth to a bunch of male parasites ready to start the entire process again on other fish. These baby parasites will disperse and find their own hosts.

It’s a nightmarish thought that something like parasites survives the way they do by taking over species. However, it’s a more common occurrence than we think. Humans alone are hosts to so many organisms that we can’t see and that we hold in our bodies. All these organisms and most of the bacteria that lives in us are too small to be noticedAs a matter of fact, 90% of our cells are not entirely human cells. Our bodies are the best representation of what an ecosystem is and should be.

The good news is that it’s rare for humans to get a parasite like the Cymothoa exigua. While these creatures primarily survive on fish, they do influence our lives somehow. We already know that these parasites like to go on snapper tongues and other fish tongues as well. As it turns out, Cymothoa exigua exists in large, widespread numbers throughout the ocean. The problem is that our oceans are filled with them, so the fish that we like to eat, the snapper for example, becomes host to these parasites. Fish sellers overlook some of these parasites, and customers may cook their food without knowing. Although they will not harm humans when consumed, it’s just a terrible thought to consume these parasites at all. Just make sure that they’re still not alive because if they were, they will be biting your tongue as well.

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