If it started as a new pond, then where did your water come from? If you only catch rainwater and there is no possibility of fish coming in with the water, then that leaves your supplier, birds/animals, or a random person putting them in the pond. THere are some links on this site on how to make a good baitfish/bullhead trap. Make two or three of them, bait them and watch them work, as well as a few good days of hook line and worm you can really do some damage in a small pond. If you get totally mad at them you can release some .12 ga on them
