Facts About the Fish Tongue Parasite

The fish tongue parasite, Cymothoa exigua, was featured in the 2012 film "The Bay". The film featured a population of tongue-eating louses that grew to enormous proportions due to toxic wastes, and then began infecting the residents of a small town on the Chesapeake Bay.

The fish tongue parasite is a parasitic crustacean isopod belonging to the Cymothoidae family. It infests fish by entering via the gills of the fish. The males reside in the fish's gills, whereas the females attach themselves onto the tongue and act as the fish's functional tongue.

To date, Cymothoa exigua is the only known parasite that is capable of replacing an organ or any other structure that it has removed from its host.

• Kingdom: Animalia
• Phylum: Arthropoda
• Subphylum: Crustacea
• Class: Malacostraca
• Order: Isopoda
• Family: Cymothoidae
• Genus: Cymothoa
• Species: C. exigua
• Common Name: Tongue-eating louse

The occurrence of the fish tongue parasite is quite widespread. It may be found from the Gulf of California to the Gulf of Guayaquil, Ecuador. Waters near Costa Rica and New Zealand also have had cases of C. exigua. The depths at which it has been found ranges from 6 ft 7 in to almost 200 ft deep.

The tongue-eating parasite infects the buccal cavity of the fish and utilizes it for growth and reproduction. The parasite reproduces sexually while it is attached to the host, and produces free-swimming larvae that begin searching for a potential host immediately after birth.

The females can grow up to 0.3-1.1 inches in length and 0.16-0.55 inches wide, while the males grow 0.3-0.6 inches in length, and 0.12-0.28 inches wide. The female shows the presence of six pairs of legs and five jaws. While this parasite mainly infects the snapper fish, it has been reported in 7 other varieties of fish.

Once the juvenile isopod enters the fish's oral cavity, it attaches itself to the fish's tongue and begins extracting blood using its claws.

As the parasite feeds on the tongue, the amount of blood received by the tongue gradually decreases and eventually the organ atrophies. Once this occurs, the isopod latches onto the base of the tongue and itself functions as the fish's tongue. It now survives by feeding on the host's blood, and on the fish's mucus.

The fish tongue parasite is a protandrous species that exhibits sequential hermaphroditism. In a protandrous species, there is sexual selection for larger females as the female size correlates with fertility. Sequential hermaphroditism implies a natural sex change of the organism during the course of its life cycle.

These ectoparasites are born as males and transform into females only upon attachment on the host tongue. If the female is absent or dead, the male will transform into a female and latch onto the atrophied tongue.

Studies have shown that the location of parasites in the host depends on the number of isopods present. If the host is uninfected, the parasite is found on the tongue. If two isopods are present, one occurs on the tongue, while the other is present in the cavity between the gills and the tongue.

In case there is presence of three or more isopods in a single host, one isopod is situated on the tongue, one in the gill-tongue cavity right behind the female, and the others are attached to the gill arches.

The first subsequent male that infects a pre-infected host, mates with the female. A female may produce around 400 to 720 eggs of which around 200 reach maturity. However, according to recent studies, the female only reproduces once in her lifetime.

On hatching, the eggs release motile offspring known as manca (pl. Mancae) that immediately begin searching for new suitable hosts by searching for chemical cues in their environment.

• The parasite infestation may cause lacerations/cuts to the buccal cavity of the host. These open wounds can be a port and breeding ground for pathogens.

• Too many cuts may also cause the host to be anemic.
• The males may start feeding on the gill tissues.
• A large infestation of parasites in the gills may even lead to respiratory issues in the host.

• In 2013 in Puerto Rico, the tongue-eating louse became the subject of a lawsuit against a large supermarket chain. The customer claimed to have been poisoned by ingestion of an isopod cooked inside a red snapper.

However, the case was dropped on the grounds that the isopods are not poisonous to humans, and also because some isopods are regularly consumed in certain parts of the world as delicacies.

• There are more than 40 distinct species of Cymothoa; however, only Cymothoa exigua is known to consume and replace the host's tongue.

The parasite is relatively harmless to humans, unless it is picked up by bare hands, in which case it bites. It is non-poisonous, and does not consume human tongues.