I've had Bluegill with them before, I treated the tank (Sorry,I don't remember what I used as it was about 4 years ago) and removed fish from the tank and removed the anchor worms with tweezers. As I remember , they liked getting into the body where the fins met the body and came out pretty easily.You can see why they're called anchor worms once you get them out. The aren't all prominant like the one that might be on your Piranha, look closely and you might be able to see more before the egg cases develop.
Good Luck.