Piranha has wierd puncture wound on it's side
I noticed my one piranha has a wierd puncture wound on it's side. We noticed it yesterday while doing some tank maintence. They are fed two times daily (flakes and freeze dried in the am, frozen and pellets at night). They are housed in a 75 gallon aquarium with just a pleco and no other fish. It doesn't look like a bite (they have bit the pleco so I know what one of their bites look like). It just looks like a single puncture wound and the hole is too big to be a tooth mark. The fish that has the wound is also the most aggressive of the two piranhas he is first to feed, gets the best pieces, and has acted aggressive to my hand once or twice while I was doing regular tank maintence (which now I have since gotten a gravel syphoner that does not require me to stick my hands in the tank). I don't know what this could be and it's too hard to take a picture. It doesn't look like a fungus or anything but should I do anything for the wound? I do weekly water changes and add a water conditioner but didn't know if I should put something else in there.
Secret to a successful life is not in playing a good hand, but in playing a poorly delt hand well.