If they are bass, you should see a black line running down the sides of their bodies. On young bass, it is usually pretty distinct and easy to see from the surface of the water. If they have the torpedo shape of the bass, they may be. If they had a lot of food, they are growing fast. Way fast. Is it possible that some were in the pond before you stocked it with the ones that you know about?
Fish get into ponds without stocking. The best idea of how that happens is that they stick to birds feet and get transplanted. Anyway, it is not uncommon to find fish in a pond that was never stocked.
