About 10 years ago, I spoke to an owner of several large West Texas ponds. He was raising HSB and feeding them food from a well known North Texas Milling Co. They cost about 50% of Purina, Cargill etc. and were fairly high protein. He said his fish were eating them and doing well. I did not ask him how well.
I called Purina and discussed it with the guy who developed the fish feeds. I had met him on several occasions but won't mention his name. He told me that he couldn't buy the ingredients that he used(Menhaden) for that price. He also said that he couldn't even buy the grain based ingredients for that $.
I suspect that most of the less expensive feed is chicken feather based. I have read that the poultry industry has, for years, tried to find more uses for the copious amounts of feathers that they wind up with.
There are an awful lot of less expensive fish feeds at farm/feed stores that I have decided to stay away from.
Disclaimer: I am not a fish nutritionist.
The label on the pellets I use lists the ingredients. Starts with fish meal, soy meal......
Don't all pellet brands have to list their ingredients on their labels? Wouldn't you know if you are buying feather protein?