My bet is that this fish was either wild caught at this size, or raised elsewhere. and THEN put in that tank. I don't feel like it grew up in there to be that size.
Awesome fish. I would love to see it in a huge tank though. Tank size to fish size ratios like that just make me feel claustrophobic plus I'd love to see that fish accelerate and swim fast after food. That is one of my favorite things to watch my red finned pickerel do.