If it was my 5 acre pond, zero.

It all depends on your goals and how many you think you'll be taking out annually. Just remember, once they surpass about 3#, they will be competing with Bass for food (i.e. live fish).

www.hoosierpondpros.com

[Linked Image from lh6.ggpht.com]
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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).