Fishermen recently discovered a parasite replacing the tongue of a weaver fish in the sea around Jersey. This might be a new species.
Tongue Eating Louse Classification
The Tongue-eating louse (Cymothoa exigua) has been known about for a long time. It is not a louse (see article about human lice, nits and 'crabs'), nor even a fish-louse. It is a rare parasitic Isopod crustacean.
- Lice are wingless insects.
- Fish-lice are crustaceans – but in a different family from the Isopods.
- Isopods are most commonly seen as ‘woodlice’ on land (about 5,000 species).
- Over 4,500 other species of Isopod inhabit the sea, and another 500 or so live in fresh water.
- Of the 4,500 marine isopods only around 700 species (all in their own Sub Order Epicaridea) are parasitic.
- Cymothoa exigua is the only species of parasitic isopod known to replace its host’s tongue. The usual host is the spotted rose snapper fish (Lutjanus guttatus), and it is normally found in the Gulf of California.
BBC NEWS recently reported the discovery of a ‘louse’ replacing the tongue of a Weaver Fish.
This creature has not been studied enough yet to know whether it is Cymothoa exigua, or a new species. (On the other side of the Atlantic, and with a different host fish, it is quite likely to turn out to be a new species.)
Parasite Replaces Host’s Tongue
- This weird isopod creeps in through the fish’s gills and attaches itself to the base of the tongue.
- The parasite sucks blood from the tongue, and the tongue slowly withers away (it does not really ‘eat’ the tongue).
- When only the muscular stump of the tongue is left the parasite attaches itself and from then on behaves like a normal tongue. (This article gives more details.)
- Once attached and behaving like a normal tongue (it is about the same size and shape as the fish’s tongue was) the parasite will have cut off the blood supply it formerly fed on, so it begins to eat scraps of food that enter the fish’s mouth.
- The fish does not seem to be unhealthy, and it continues to behave normally and grow. Only looking in the mouth reveals the bizarre ‘passenger’.
Earlier Discovery of Tongue Eating Louse in UK
In 2005 another tongue eating louse was found – this time in the mouth of a Red Snapper (Lutjanus campechanus) bought in a London market.
Since the Red Snapper comes from the Atlantic (Gulf of Mexico) it is conceivable that there are several species of ‘tongue-eater’ waiting to be discovered.
Luckily the Giant Isopod (Bathynomus giganteus) – see image below – is not a parasite. It snuffles along harmlessly on the Atlantic seabed. But, if some of the larger marine fish are discovered to host as yet undiscovered mouth-eating lice, the mind boggles!
Reference: BBC NEWS (9 September 2009)
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(Click on the images below to enlarge them.)
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