A good pond builder could find enough subsoil clay to line the basin with clay so the pond holds water better. Minimum clay liner thickness is usually 2 ft and best is 8ft thick in the upper 6 ft and below that depth is usually a clay 'belly' basin. Find and use the best pond builder in your area.
For a small pond like you are planning and to grow a decent amount of fish you will need to add high protein fish food (40%+) to fish that have previously been pellet trained. Check out an eastern PA fish farm maybe close to you called Shultz's for good quality pellet trained fish.
http://buybass.com/It might be worth a trip there to get quality fish.
There are a few small ponds near me that have only yellow perch (YP)and they keep growing well due to an annual harvest and being fed pellets. A few predators may help with eating extra perch young but it may not be necessary if you manage the perch well. With perch only and feeding you could probably harvest 15-25 8"-10" perch each year from a 50x50 pond. You could add a few (15-25) trout each fall, feed them and harvest them in June-Jul or they may live year round with the right water quality. You would have to try it and see once the pond is built. If the pond could somehow be spring fed that may help with improved water quality and long term survival of trout and YP. If not just YP will also work if done properly. If feeding the fish, artificial aeration is very beneficial to optimum water quality in a small pond so plan to provide for that (electrical within 200ft) feature.
There is quite a bit of info in past posts here about fish options for a small pond similar to that you are planning. The problem is the info is not all in one place so you will have to do some searching and asking questions.
