We've had luck establishing threadfins in ponds as small as 1/10 acre. My dad has a 1/10 pond in north texas, near the oklahoma border that was stocked with threadfins 2 years ago. The pond has no lmbs but has hybrid stripers and catfish. He caught some shad in a cast net this fall. Pond is only 6-7 ft deep. I'm not saying that shad will make every winter in this small pond.
Also we've had luck establishing shad in ponds as small as 2 acres with lmb predation pressure. The key for success is fertile water with some deep-open areas, and adult shad that are ready to spawn.
We surveyed a 2 acre pond this year for a new customer. His pond was loaded with threadfins and chunky bass. As a matter of fact, we ended up harvesting about 50 lbs of chunky male lmbs from this 2 acre pond to help out the females. In this particular case the threadfins were the primary forage base, more than his populations bluegill or redear sunfish. This pond had good natural plankton bloom and some deep open water.
Odds for threadfin survival and establishment in a pond or lake depend mainly on environmental conditions, which are not necessarily related to surface acreage. This is my very humble opinion. I'd love to hear from folks who have stocked threadfins.
