All fish have the ability to go out as S0s, S1s or S2s. What dictates that is genetics, but so do food availability, water temperature and development.
Just listen to this one interesting thing: In the farming industry—I farmed Chinook for many years—when we entered S0 smolts, every farm had issues keeping them alive and required antibiotics. If they re-entered an S1 smolt, that was a non-issue; we'd get 96% survival.