July 17, 2024, 6:12 am | Read time: 3 minutes
Some fish look as though they have an extra pair of eyes on their tongue. But this is not the case. There is an explanation for this strange sight.
There are many animals in the ocean that people respect or even fear. Great white sharks or frogfish from the deep sea are some examples. However, there is another creature in the sea that is much smaller and creepier. Some fish appear as though they have eyes on their tongue. However, there is a disgusting explanation for this strange sight.
Parasites infesting the tongues of snappers and clownfish
Cymothoa exigua, also known as the tongue-eating louse, affects many snapper fish in the Eastern Pacific. However, it is also frequently found in clownfish and surgeonfish. Impacted fish look as if they have an extra pair of eyes on the tips of their tongue.
The truth is, at this point, the fish no longer have a tongue. This is because the Cymothoa exigua isopod infests the fish, causing them to lose this vital organ. They penetrate the gills of the fish and bite into a vein in their underside, sucking out the fish’s blood until the tongue dies from anemia.
At this point, the parasite has two options: either leave the fish’s mouth, which they can no longer survive without, or simply replace the tongue. In most cases, the water lice choose the second option. In this way, the infected fish can continue to feed with the “fake tongue”, and the tongue-eating louse can continue to suck its blood. The fish and the parasite are then forced to live together until the fish dies and the isopod looks for a new host. This makes Cymothoa exigua the only known parasite that can functionally replace an organ in its host.
“Tongue with eyes” even reproduces inside the fish’s mouth
This parasite does not particularly bother the affected fish. Some are a little anemic or keep their mouths open more often, the larger the isopod becomes. However, a study also indicated that fish infected in the early stages of life exhibited a higher mortality rate. However, it has not yet been possible to confirm whether this was related to the loss of their tongue.
If these facts weren’t scary enough, hold on tight. The parasites multiply in the mouths of the fish they infest, with female isopods acting as a “tongue with eyes” in the fish’s mouth. However, they do not begin like this. When they enter the host, they are still males. As soon as they have docked onto the tongue, growing from 15 millimeters (about 0.59 inches) up to 28 millimeters (1.1 inches), they transform into females.
If a free-swimming male wants to reproduce, he also penetrates the gills of the infested fish, which are located behind or next to the female. The act of mating then takes place. However, it is likely that the afflicted fish is no longer aware of this and passively endures the process.
If you are completely distraught from hearing this information, have no fear. Based on current knowledge, the tongue-killing isopod is believed to pose no threat to humans.
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Sources
- Ruiz, A., & Madrid, J. (1992). Studies on the biology of the parasitic isopod Cymothoa exigua Schioedte and Meinert, 1884 and its relationship with the snapper Lutjanus peru (Pisces: Lutjanidae) Nichols and Murphy, 1922, from commercial catch in Michoacan. Ciencias Marinas, 18(1), 19-34.
- OceanConservancy.org, “Tongue-Eating Louse Actually Eats Tongues” (accessed 24.03.2024)
- Futurism.com, “Cymothoa Exigua: Meet The Sex-Changing, Tongue-Eating Parasite“ (accessed 24.03 .2024)