DaveB do you have the pond surveyed for standing crop of fish ( how many lbs of what type of fish per acre) ?

If 50 lbs per acre worked well I would guess that you should subtract from 50 your standing crop of tilapia per acre. For example if 15 lbs of tilapia per acre survive winter then I would add 35 lbs. But that is a WAG. It would be better to have someone do the survey and give an answer based on what they see wrt #s and lbs and size of fish.

The questions you and LWJ are asking are very hard to answer with any degree of accuracy with out seeing/knowing the pond conditions ( balance and population status).