DPMESA,
I think the growth is very respectable. 1.5 lbs gain per year is good. Also 21.5 inches in two years after stocking at 7" avg length is good too. Might surprise you but the average time it takes a 7" CC to eclipse 20" in OK reservoirs is 6 years. So this is the difference feed is making for them.
There has been mention that the CC was on the light side. When I first checked a table that I acquired some years ago, it implied the CC was 100 RW. But searching another on the web it implied 86 RW. The chart that Jason referenced implies 76 RW. The RW in part depends on which chart is referenced. That said, Jason's fish demonstrates that it has potential to consume more than it did.
So was the CC underfed? I am loathe to suggest that. What we are looking at is a CC that is growing 3 times faster than wild counterparts making a tougher living. You made life a lot easier for them. Should you feed more? That depends on you. What I would tell you is that the CC are competing with your BG and LMB for feed and you will have to feed more than what the CC would need by themselves. It will be harder to push their growth than it will to reduce their competition.
I like that you ate that wonderful CC. Eat some more of them! If you want to grow as much harvest weight of them for the least amount of feed, then crop them heavily. A 12" CC can grow to 2 lbs in a season. The bigger they get, the worse the FCR and harder it is to feed them enough to grow them at the initial rates you observed. It is very likely that if you harvested all you could catch > 18" that some would still grow into larger lengths providing larger fish in the future. You could consider a ladder of 12" CC each year. A lesser density of them to help them grow faster (something like 25 per year) may be a good idea.
