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Yes, it’s true. Parasite gives new meaning to ‘tongue in cheek’

Does this Facebook post show a “terrifying” parasite, as it claims to? It has been shared on Facebook in South Africa, and was marked as possibly false by Facebook’s fact-checking system

The post reads: “There is an absolutely terrifying parasite that lives around California: cymothoa exigua. This creature devours the tongue of its host fish, pink snapper, to ... Replace it!” The photo posted shows a louse-like creature inside what looks like a fish’s mouth.

Could this grizzly image be real?

Parasite does not eat fish’s tongue, but replaces it

According to an article published by the American Association for the Advancement of Science (AAAS) in September 2012, the Cymothoa exigua, also known as the tongue-eating louse, is a type of parasitic isopod.

AAAS spoke to Dr Stefanie Kaiser, a freelance marine biologist who in 2012 was a fellow at the National Institute of Water and Atmospheric Research in Wellington, New Zealand. 

She said that this parasite enters the fish through the gills and uses its legs to attach itself to the base of the tongue of the host fish. 

Kaiser said that the parasite does not actually eat the fish's tongue, but sucks blood from the tissue, so that the tongue eventually withers away. 

The parasite then remains attached to the tongue base and “becomes a living substitute”, Kaiser said. It feeds on the host’s blood or mucus, while the fish eats its usual diet. 

The parasite can remain attached to the fish for several years, grows as the fish grows and eventually detaches.

Only known example of parasite replacing organ

A video made by the US’s Public Broadcast Service’s NOVA programme in February 2013 explains the parasite and how it attaches itself. The UK’s National History Museum also illustrated how the Cymothoa exigua can replace the tongues of clownfish in a short video published in November 2017. 

There seems to be no evidence to contradict a 1983 journal article which claimed that the Cymothoa exigua was the only known instance in the animal kingdom of a parasite “functionally replacing an organ of its host”. Unfortunately for those prone to nightmares, this “terrifying parasite” is real. Taryn Willows


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