Not the first to be host to a parasite! Another that has been mentioned on these boards before is Cymothoa exigua, a louse that enters a fish and replaces it's tongue - yes, the fish uses the louse as it's tongue once the old one has withered away thanks to the parasite. It's the only known parasite to actually replace a functioning body part.
No real harm to the fish, but you wouldn't want to find one when you're just about to eat a barbequed fish!
