I think snakebite has a very good question. Assuming that, due to clear water/heavy predation, you expect minimal reproductive success from tilapia stocked as adults in the spring/summer, the fall-fingerling stocking would render most return on investment. Adults stocked in the spring/summer may reproduce all season, but most all of the fry may fall victim to predation. Fall-fingerling tilapia stocker survival rates can be exceptional, compared to fry survival. In addition, they may double in size before the winter die-off, and would represent more bang-for-buck than stocking adults in spring/summer.