Wrong answer. It 'kills' the tongue, then 'replaces' it. It says that the fish is actually able to use the parasite as its own tongue, being able to manipulate it. Then the parasite gets to eat some of the food that the fish eats. Its more in favor of the parasite, but it appears that as long as the fish gets enough food to eat, that it isn't harmed in any way. If the fish were to die, the parasite would have to find a new host, so that doesn't really benefit it.