bitten

Hi everyone, I am new in this forum, but I really need your help. I have 6 red-bellied piranhas in a 720-liter freshwater tank. Four of them I got "second-hand" when they were already a few years old, they are now about 25 cm long. I added two smaller piranhas less than a year ago, those are now...

A few of them got bitten off halfway, does anyone have experience with them growing back?