It depends on many factors. Size of the water, forage in the system, other game fish in the systerm, anglers needs/wants, ect. They are currently experimenting with stocking yearlings instead of fingerlings in 3 or 4 lakes in pa (all western lakes). Many lakes get tigers because they grow faster than pures, and they are easier to raise. My vote would be to stock only pures and stock them as yearlings.