As the title states, I'm looking for a large growing fish like a mahseer or something similar that can survive a cold NJ winter. I'd like to put something different in my koi pond. It gets cold enough to freeze over if I didn't have one of the pumps and the air pump running all winter. Are there any fish that can/will survive? Also cant be too aggressive. Don't want it to beat up my koi. The pond is 22'x18' and 40" deep. Any ideas are appreciated.