If you had a small 1/4-1/2 acre pond and you wanted to be surprised at the catch every time you dropped a hook in, what would you use to have a
"Sustainable/balanced" population?
Using those terms loosely
Just to emphasize my two favorite replies.
Steve_ mentioned that put and take is a good option. It's just difficult to have the predators spread across the different size classes to have a really good balance of predator and prey.
Snrub mentions SMB as an option. For a pond this small, a single reproducing predator might also be an acceptable route depending on your goals. SMB are the better of these choices because they would attain a greater standing weight than LMB. You have to be willing to harvest a specified weight of them each year to keep a new crops of pan sized SMB coming. You don't have to have any other fish in the pond to achieve a balance, they achieve their own balance each year ... then you crop them so they can do it again the next year. You could harvest annually as much weight/acre of SMB as you could weight/acre of LMB and BG in a properly balanced larger pond. So it is a productive scenario that is easier to manage than a predator prey combination.
I will add some additional thoughts.
For a small pond to provide a lot of fishing catches, you need the weight of the fish concentrated in catchable sizes. When a large proportion of the weight of fish are sub-catchable or are too small to be memorable its a stretch to call the fishing good. When the approach is put and take, it is useful to have fish that grow to a harvestable size in one season. When they are carried from year to year, this will reduce the number of catchable fish you can have and they can become difficult to catch. Along the lines of completely put and take you can plan for fishing seasons in the temperate weather of Fall and Spring. Fish that you don't catch in the fall that can overwinter can be outsized bonuses the following year. There are a lot of options but the number and weight of fish you could grow annually in a 1/4 acre pond might surprise you.
