"So, naturalists observe, a flea has smaller fleas that on him prey; and these have smaller still to bite ’em; and so proceed ad infinitum."
- Jonathan Swift

January 26, 2010

January 26 - Cymothoa exigua


Cymothoa exigua is a parasitic isopod with a very odd and gruesome life cycle. 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. The female then makes its way to the fish’s mouth where it uses its front claws to attach to the fish’s tongue. It begins to feed on the blood in the tongue until the tongue eventually atrophies completely. The isopod then takes the place of the tongue in the mouth, attaching to the floor of the mouth and the stub of what is left of the tongue with its hind pereopods. There it lives out the rest of its life – even letting the fish use it like its old tongue, holding prey against its teeth. Although these parasites were long thought to be restricted to the Gulf of California and environs, recently one turned up in the mouth of a fish that was caught off the coast of the U.K.

19 comments:

  1. More information about C. exigua available on Carl Zimmer's blog "The Loom". Enjoy!
    http://blogs.discovermagazine.com/loom/2009/12/08/lets-haunt-their-dreams-forever/

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    1. Also in Mr. Zimmer's book PARASITE REX.

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  2. I wonder if the fish knows what happened to its tongue.

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  3. Obviously it's damaging when the parasite is in the process of biting off the fish's tongue, but does the fish ever heal or does the stub continue to be a wound?

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    1. It does hurt the fish a little, but not enough to kill it or really injure it.

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  4. The isopod doesn't bite off the tongue - it is depleting it of blood so that the tongue eventually atrophies. There does not seem to be any evidence of the tongues healing that I have seen.

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  5. I am looking for a life cycle for this cymothoa, though thus far I have been unable to do so. Is it simply just such a newly discovered ectoparasite that no such research has been conducted?

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  6. David, do you mean where and when the female lays the eggs and how the juveniles find the fish?

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  7. Youtube video of cymothoa exigua:

    http://www.youtube.com/watch?v=xH1c9ZiPnbU

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  8. This video likely is not of Cymothoa exigua, given the host and location, but it's a similar isopod. Nice closeups!

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  9. Is there any more information that can be found regarding how, when, and where this particular species mates? It seems there is very little detailed information on it as David mentioned.

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  10. I recently caught 3 fish in The Knysna Lagoon (South Africa) all with these things attached to the outside of their gills. All 3 had two attached.

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  11. Those were almost certainly not this species, given the location on the fish and in the world. But, sounds like you found yourself some other parasitic isopods!

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  12. Is there any place I can get more information about this parasite? My parasitology class is also doing a blog where we get to choose the parasite we will discuss and I just found this one too interesting to not do. We are reading Parasite Rex as one of our materials but have not gotten to the part where he talks about so if that could be located that would be great too. Thanks for any help with this parasite.

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  13. We just caught a snapper and a yellowtail off the great barrier reef in Belize, specifically Caye Caulker. While cleaning the fish, which had been together in a bucket for a couple hours, one of these guys was sitting on the mouth of the yellowtail. The snapper died first, so we were wondering if this parasite switched to the smaller yellowtail...though it was pretty well affixed to the ridge of the yellowtail's mouth it seemed so large that it may have come from the tounge-less snapper we caught. Anyhow, it was GROSS!

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  14. Im doing this for a science project and I need sources. What are your sources? Thats nazziatin by the way.

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  15. JP - go to Google Scholar (http://scholar.google.com) and look up "Cymothoa exigua".

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  16. I went fishing in the town of Don in Tasmania in 2009, and all the fish i took back to camp with me had these 'tongue biters' crawling out of the mouth of the fish when i was cooking them.

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