I had one that was a good 12 inches long. I'm sure they can get bigger than that, but it was the largest I had ever seen. I sold the tank a while back when I moved into a smaller place. I wonder if he is any bigger now.
How nasty was he? I think they are gorgeous, but I have attempted three in the 4-7" range at various times and they all were moody and annoying to the other fish. One kept killing new fish for some reason -- it was a big tank and I made the other fish very dissimilar. Didn't matter...I ended up trading in all three.
Yes, he was a very nasty fish, and he lived alone in his tank. It made for a nice species tank with lots of rock caves for him to hide in. It was a FO tank with some large snails and big hermit crabs for cleanup. They are very beautiful fish but predatory and territorial. He did hide a lot, but he'd come out and cruise the tank looking for food when people came into the room.