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Cymothoa exigua

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Title: Cymothoa exigua  
Author: World Heritage Encyclopedia
Language: English
Subject: Fish diseases and parasites, Cymothoidae, Parasitism, Male, Cymothoida
Collection: Animals Described in 1884, Crustaceans of the Eastern Pacific Ocean, Cymothoida, Parasitic Crustaceans
Publisher: World Heritage Encyclopedia

Cymothoa exigua

Cymothoa exigua
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Crustacea
Class: Malacostraca
Order: Isopoda
Family: Cymothoidae
Genus: Cymothoa
Species: C. exigua
Binomial name
Cymothoa exigua
(Schiødte & Meinert, 1884)

Cymothoa exigua, or the tongue-eating louse, is a parasitic crustacean of the family Cymothoidae. This parasite enters fish through the gills, and then attaches itself to the fish's tongue. The female attaches to the tongue and the male attaches on the gill arches beneath and behind the female. Females are 8–29 millimetres (0.3–1.1 in) long and 4–14 mm (0.16–0.55 in) in maximum width. Males are approximately 7.5–15 mm (0.3–0.6 in) long and 3–7 mm (0.12–0.28 in) wide.[1] The parasite severs the blood vessels in the fish's tongue, 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.[2]


  • Behavior 1
  • Distribution 2
  • Reproduction 3
  • Influence on humans 4
  • Popular media 5
  • References 6


C. exigua extracts blood through the claws on its front, causing the tongue to

  1. ^ Richard C. Brusca (1981). "A monograph on the Isopoda Cymothoidae (Crustacea) of the Eastern Pacific" ( 
  2. ^ a b c R. C. Brusca & M. R. Gilligan (1983). "Tongue replacement in a marine fish (Lutjanus guttatus) by a parasitic isopod (Crustacea: Isopoda)".  
  3. ^ Vernon E. Thatcher, Gustavo S. de Araujo, José T. A. X. de Lima & Sathyabama Chellappa (2007). (Bloch & Schneider) (Osteichthyes, Carangidae) of Rio Grande do Norte State, Brazil"Oligoplites saurus sp. nov. (Isopoda, Cymothoidae) a buccal cavity parasite of the marine fish, Cymothoa spinipalpa" ( 
  4. ^ a b Ernest H. Williams, Jr. & Lucy Bunkley-Williams (2003). "New records of fish-parasitic isopods (Cymothoidae) in the Eastern Pacific (Galapagos and Costa Rica)" (PDF). Noticias de Galápagos (62): 21–23. 
  5. ^ "Tongue-eating bug found in fish".  
  6. ^ "Tongue-eating louse found on supermarket snapper".  
  7. ^ A. Ruiz-L. & J. Madrid-V. (1992). (Pisces: Lutjanidae) Nichols and Murphy, 1922, from commercial catch in Michoacan"Lutjanus peru Schioedte and Meinert, 1884 and its relationship with the snapper Cymothoa exigua"Studies on the biology of the parasitic isopod .  
  8. ^ "Rare tongue-eating parasite found".  


In The Apocalypse Codex by Charles Stross, a pseudo-Christian apocalyptic sect takes over human beings by implanting giant Cymothoans provided by a malignant entity into their mouths, where they take over the function of the tongue while controlling the victim's mind.

Anime Parasyte: The Maxim depicted similar parasites.

C. exigua was depicted in the 2012 film The Bay, in which the residents of a small town on the Chesapeake Bay were infected by the parasite, and died as a result. The film proposed that C. exigua grew to large sizes quickly due to the steroid-laden chicken feces dumped in the bay.

Popular media

In Puerto Rico, C. exigua was the leading subject of a lawsuit against a large supermarket chain. Because C. exigua is found in snappers from the Eastern Pacific and is shipped worldwide for commercial consumption, contamination by the parasite is inevitable. The customer in the lawsuit claimed to have been poisoned by eating an isopod cooked inside a snapper. This case, however, was dropped on the grounds that isopods are not poisonous to humans and some are even consumed as part of a regular diet.[4]

It is currently believed that C. exigua are not harmful to humans unless picked up alive, in which case they can bite.[8]

Influence on humans

Not much is known about the life cycle of C. exigua. It exhibits sexual reproduction. It is likely that juveniles first attach to the gills of a fish and become males. As they mature, they become females, with mating likely occurring on the gills. If there is no female present, within a pair of two males, one male can turn into a female after it grows to 10 millimetres (0.4 in) in length.[7] The female then makes its way to the fish's mouth where it uses its front claws to attach to the fish's tongue.


In 2005, a red snapper parasitised by what could be Cymothoa exigua was discovered in the United Kingdom. As the parasite is normally found off the coast of California, this led to speculation that the parasite's range may be expanding;[5] however, 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.[6]

C. 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 metres (6 ft 7 in) to almost 60 m (200 ft) deep. This isopod is known to parasitize eight species in two orders and four families of fishes [7 species of order Perciformes: 3 snappers (Lutjanidae), 1 grunt (Haemulidae), 3 drums (Sciaenidae), and 1 species of order Atheriniformes: 1 grunion (Atherinidae)]. Females of this isopod were found in the mouths of three species of snappers. New hosts from Costa Rica include the Colorado snapper, Lutjanus colorado and Jordan's snapper, L. jordani.[4]


There are many species of Cymothoa,[3] but only C. exigua is known to consume and replace its host's tongue.

will detach itself from the tongue stub after some time, leave the fish's mouth cavity, and can then be seen clinging to its head or body externally. It is not fully known what then happens to the parasite in the wild. C. exigua When a host fish dies, [2]

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