Crayfish doesn't stand a chance. Cichlids and Pacu will devour poor guy. He might last about 3 days. I bought 3 BIG ones from lfs and he told me that they wouldn't last in my tank of Jack Dempsey's and Firemouths........But, I wanted them so bad, I bought them. Three days later, there were shells, but no meat.
I don't recommend it. I would get them if I had schooling fish that were fast enough to get away from them. They don't back down from anything, but they just can't handle the cichlids!!!
Good luck, man!!!