The Tongue-Eating Louse

As most anglers would have noticed it is unlikely to catch a Pollock without this little creature attached. The norm is to find it attached to the tongue but it can sometimes be found on the top of the head. The creature in question is Cymothea exigua or Tongue-eating Louse. Although it isn’t a parasite in its true sense, but a Crustacean like a common crab, (try explaining this to its host fish) it behaves just like a parasite and is known as a parasitic crustacean.

This “parasite” enters through the fish's gills and the female attaches itself to the base of the tongue while the smaller male grips onto the gill arches behind and beneath the female. This little monster stunts the growth of the tongue and eventually shrinks it due to lack blood flow.

Cymothea exigua attaches itself to the base of the tongue’s muscles and completely replaces the tongue to the point that the fish can actually use the parasite as its own tongue. This is the only known example of a parasite successfully replacing a host’s organ and doesn’t seem to bother the host at all. The parasite begins by feeding on the host’s blood and then on its mucus. It doesn’t appear to show any interest for the food the fish itself eats. There are other types of Cymothea but only Cymothea exigua is known to consume and replace the host’s tongue.

There is no danger to humans or the consumption of the host fish. However, if not handled correctly this parasite will grip strongly onto your finger with its incredibly sharp and strong six pairs of legs and you might even get bitten.

In the picture you can just make out the male’s claws in the gills on either side.

Normally a Pollock this size (just under 2 lbs / 1 kilo) would have been released but I wanted to show you this parasite. The Pollock was later cooked and eaten and, I must say, was very tasty!