Oliver,

If yo put 40lbs of fingerlings in a 120 gallon container. as they grow the lbs per gallon changes.

so you will need to remove fish to keep the ratio correct?

I have roughly 40 to 44 pieces of Tilapia in 40 gallons of water. All chemistry is fine and within good range only when I added additional water when I went from gravel to float beds did I experience a slight Nitrite spike but it has not hurt the fish. everything else stayed the same. After a week the Nitrite level went back down. Nitrate levels never changed ammonia levels never changed and pH is around 6.6-6.8.

So When I put the the tilapia in I put in forty Tilapia fingerlings they are growing and range in size from 3 inches to 7 at present. I am going to leave them as long as I can to see how big I can grow them in this same 40gallons of water.