Does anyone have a recommendation for the mesh size to hold 3/4" fish? What is too big, hole wise?

I bought a 3mm X 3mm hole size net cage 2M X 2M X 1M for 3/4" tilapia & they seemed to have disappeared. I have not seen them since the second day. No holes or tears in the netting. My goal was to grow them to 4-6" & release them into the pond.