Ponds are captivity rearing areas and Tilapia requires high levels of oxygen and extremely clean environment, therefore they should not expect the big sizes though such size can be achieved but after longer periods.
They are advised to ensure proper management, and to sell fish at an acceptable size other than waiting for the big sizes. They should sell and stock and sell whenever fish attains table size. Waiting for the very big size is not cost effective for someone who is after profits.