The problem with mine could have been that he had been fed live before my getting him. When I got him he was already over a foot. Would not eat the first several months (I don't feed live). I practically force-fed him his first piece of fish - it looked like he bit it in self-defence and swallowed it as I got desperate and was "harassing" him around the pond with a piece of fish on a 3' grabber tool. I had another success like that once more. After that he lived in a large clay planter half and ate sporadically when I threw food inside. I could not see what was happening there. Sometimes I felt a strong blow to my tongs but I didn't know whether he was snatching food to eat or defending himself. There were other fish in the pond, so I was never sure he ate. He didn't get skinny though. After about a year, one day he passed away for no reason that I could see, at ~2'. He was one of the strangest fish that I cared for. I could not figure out how to make him happy, comfortable, and thrive... in a 4000 gal pond, 40'x6'x3' with lots of hiding spots, good water, and a 100 of other monster fish around.
This experience made me sad but determined to try again.