Well, not saying anyone is doing anything wrong, but considering catfish are some of the most effecient metabolizers of food into size, I would expect a faster growth rate. I believe the American Yellow Cat, pratically has a 1.5 to 1 lb of feed to lb of growth ration.
Compare that to Chickens-the most effecient warm blooded animal- has a growth effecieny rate of 3.5 lbs to 1 lb. We pay a high price to be warm blooded.