George, the reason why you saw success with Mozambique Tilapia is because according to Texas Parks and Wildlife, that's the only species that is legal for you to stock in your ponds.
It's been a while now since I've been playing with stocking numbers of Tilapia for algae control (not as long as Rex tho), and the reason (I believe) why we need higher numbers (per acre) of Tilapia than you do is that we have to wait longer in the year to stock Tilapia than you do. The FA gets a larger foothold, and takes more Tilapia per acre to get it under control.
Just like when Dave Davidson and Bob Lusk stocked tilapia at what I think was 10x the stocking rate that you are successful with, they didn't have success. The FA got way ahead of the Tilapia in their case. Same up North.
Tilapia cost more up North because of two reasons. 1) If you keep them over the winter, we have 5-7 months that we have to heat the water to keep them alive and flourishing in enough numbers to stock ponds. That takes energy, and energy costs $$. 2) If we don't overwinter the Tilapia, we have to buy them from some place down South, and have them shipped up here. Diesel fuel, insurance, O2, vehicle and equipment costs, and drivers wages all add to the cost that you guys down there don't have.
