how many 4-5" tilapia do you think my tank can support over the winter?

I was caught a little off guard by how quick my big tilapia became inactive.My pond water temp went from low 80's to 60 deg. in about 3 wks! So, i didn't catch as many big ones as i wanted, for eating purposes. Next year i'll havest them in late summer,when it will be a lot easier.