I haven't kept piranhas long(about 1 month) but I have researched them a fair bit before buying and my own personal experiences and what I have read seem to indicate you are right. I bought my 3 RBP's at around 1-1.5" and they are now about 2-2.5" and right away I started giving them live feeders(always quarantined first), frozen prawns, earthworms, flake food, frozen fish, and frozen blood worms and I have not had them reject a single food even once, so I would have to agree that it is easier to train smaller juvenile piranhas(at least Pygocentrus Nattereri) to eat a more varied diet. P.S. that thread was a very interesting read, good work : )