about flowerhorn fish

Question
yesterday i took my flowerhorn to my friends place .i put him into big tank with piranha ,  but piranha attack him on his caudal fin . so my question is will it come back.

Answer
Why would you put a fish into a piranha tank? Hopefully, it was done innocently and not to see what would happen. Sometimes the fins grow back and sometimes they don't. It all depends on how much of the fin is left. Please, do NOT ever put a passive fish into a tank with a meat eating fish.