As far as nutritional value of feeders, what you feed them is what makes them nutritious or not. The variation from tank bred species to species is minimal. I think you would be interested in something that is a prolific breeder.
I bought four Nile Tilapia < 3" this January, two of the four are now closing in on a foot long. One of the two larger (I assume a male) has turned a shade of pink/ red, dug a huge nest and is now chasing the other three around the tank. Hopefully that is a mating in process and I will be swamped with uber-fast growing Nile Tilapia as feeders!
convicts! right now i have a batch with my pair in the 112 ( just hatched today or lastnite sometime *wasnt home* ) so well see how many survive my 2 hungry oscars!