IS THIS SAFE... PLEASE READ?

Well I have a tank of piranhas and I always feed them frozen mice and today I decided to feed them a live mouse because the pet store was out of medium size. So I put the mouse in the tank and they didn't eat it they were scared of it. So I took the mouse out of the water and I stabbed it with a steak knife and it died. Then I fed it to them again and they ate it. So later I thought what if there was something harmful to my fish on the knife. Are they going to be ok?