It's just crazy genetic variation. I've never power fed or anything like that. The huge males all were 'normal' the first few months then had a wild burst of growth in a short period. These giants are the outliers but there are about 4 others in the 125 that rival this size. In every generation there's about 3-5% fry that are huge compared to the others and with fair regularity they grow giant sized. So far all the 'giants' are of the 2nd generation. Some of the pink males show promise but have the body type of their fathers Mongo and Slade. Those two resemble thick submarines.
The bulk of the males (G2) were mid sized and donated last year.
There's about 4 fry out of Squiggy and Flash (G4) that are already showing this 'jumbo' trait. This from a batch of 50.