Cymothoa Exigua

Detailed information about Cymothoa exigua behavior, characteristics, distribution, and reproduction is available on this web page. Scroll this page down to collect more details.

About Cymothoa Exigua

Cymothoa exigua is a parasitic isopod of the family Cymothoidae which is also known as the tongue-eating louse. This parasite enters fish through the gills and then attaches itself to the fish’s tongue. The parasite severs the blood vessels in the fish’s tongue, causing the tongue to fall off. The size of the male and female also varies and also the attachment area varies. The parasite is dangerous for the fish and also, the reason for the death of the fish.

This is isopod just like crabs and lobster and is a fish parasite. The females can grow to about an inch in length and males about half of that. It is the only organism to replace the entire organ of its host species. It mostly targets snapper but has been seen in 7 other species. These organisms are known as a protandric hermaphrodite, which means they start their lives as the males and later switch sexes in their life cycle.

Cymothoa exigua

Characteristics of Cymothoa Exigua

The parasite enters fish through the gills of the fish and then attaches itself to the fish’s tongue. The females attach to the tongue and the male attaches on the gill arches beneath and behind the female. The size of the females is a little longer than the males. The females have the length about 8-29 mm while the males have just 7.5-15 mm length. The parasite consumes the blood vessels from the fish’s tongue which causing the tongue to fall off. It then attaches itself to the stub of what was once its tongue and becomes the fish’s new tongue.

Cymothoa Exigua Behavior

Cymothoa exigua extracts blood through the claws on its front which causing the tongue to atrophy from lack of blood. The parasite then replaces the fish’s tongue by attaching its own body to the muscles of the tongue stub. It appears that the parasite doesn’t make any other damage to the host fish. This is the only known case of a parasite assumed to be functionally replacing a host organ. When a host fish dies, it will detach itself from the tongue stub after some time, leave the fish’s mouth cavity.

Cymothoa Exigua Distribution

Cymothoa exigua is quite widespread. It can be found from the Gulf of California south to north of the Gulf of Guayaquil, Ecuador, as well as in parts of the Atlantic. It has been sampled in waters from 2 meters to almost 60 m deep. This isopod is known to parasitize eight species in two orders and four families of fishes. In 2005, it was discovered that red snapper parasitized by C. exigua in the United Kingdom. It is also possible that the isopod traveled from the Gulf of California in the snapper’s mouth, and its appearance in the UK is an isolated incident.

Influence on Humans

There is no such case come in light due to this parasite. These are currently believed that these are not harmful to humans unless picked up alive, in which case they can bite. Once a customer claimed that he have been poisoned by eating an isopod cooked inside a snapper. This case was later dropped as isopods are not poisonous to humans and some of the peoples even feed on the basis of the regular diet.

Interesting facts of Cymothoa Exigua

  • Cymothoa exigua is a parasite isopod.
  • The parasite attaches to the fish by entering through the gills.
  • The female attaches to the tongue while male attaches on the gill arches beneath and behind the female.
  • The female has the large length as compared to male.
  • The length of the female is about 8-29 mm and male 7.5-15 mm only.
  • These are nonpoisonous for the humans.
  • These are able to changes their gender in after life cycle.


This is not much information about the life cycle of the Cymothoa exigua. It exhibits sexual reproduction as per some researches. Firstly, juveniles attach to the gills of the fish and become males. As they reach the maturity, they become females, with mating likely occurring on the gills. If there is no female present, then from the pair of two males, one male will become female after it grows more than 10mm in length. The female then makes its way to fish’s mouth and attached to the fish’s tongue by using its front claws.

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