A rare parasite which burrows into host fish before eating and replacing their tongues with itself has been found off the Jersey coast. Fishermen near the Minquiers – islands under the jurisdiction of Jersey – found the isopod, a type of louse, inside a weaver fish.

Marine researcher Paul Chambers, from the Société Jersiaise, was one of the fishing party and identified the find. He said he was surprised to find the isopod away from the Mediterranean sea. Isopods are normally about 2cm (1in) long and live in fish, surviving on the animal’s blood, in warm waters.

Mr Chambers said: “When we emptied the fish bag out there at the bottom was this incredibly ugly looking isopod. Really quite large, really quite hideous – if you turn it over its got dozens of these really sharp, nasty claws underneath and I thought ‘that’s a bit of a nasty beast’.

“I struggled for weeks to find an identification for this thing until, quite by chance I stumbled across something that looked similar in a Victorian journal. Apparently there’s not too much ill effect to the fish itself except it’s lost its tongue.”

[ Read the full article ]

Cymothoa exigua is a parasitic crustacean of the family Cymothoidae. It tends to be 3 to 4 cm long.

This parasite attaches itself at the base of the spotted rose snapper’s (Lutjanus guttatus) tongue, entering the fish’s mouth through its gills. It then proceeds to extract blood through the claws on its front three pairs of legs.

As the parasite grows, less and less blood reaches the tongue, and eventually the organ atrophies from lack of blood. The parasite then replaces the fish’s tongue by attaching its own body to the muscles of the tongue stub. The fish is able to use the parasite just like a normal tongue.

It appears that the parasite does not cause any other damage to the host fish. Once C. exigua replaces the tongue, some feed on the host’s blood and many others feed on fish mucus. They do not eat scraps of the fish’s food.

This is the only known case of a parasite functionally replacing a host organ.