I have a small 3/4 acre pond next to my home that I dug with my backhoe in 2003. In 2004, it filled up and the water remained dark brown and muddy looking. In 2006, I bought 200 channel cats from Tyler Fish Farms just outside of Tyler, as wells as coppern nose bluegill and fathead minnows.
Last summer, we started catching bullhead catfish. The year before we never cought any, and the ones that we have cought are very small. The channel cats are 2 to 3 pounds and larger, but the bullheads are just a few ounces. We thought they were baby channel cats until I posted pics of them here and learned to tell the difference in the fins. They are also a yellow color compared to the channel cats.
I guess the possibility exists that bullheads were mixed in with my channel cats. I couldn't say 100% that it didn't happen, but I don't think so. They have a very good reputation and I watched them get the channel cats out of their tanks inside the barn when I bought them. Every fish looked the same to me, but even more important, they would destroy their client base and reputation is they sold something like bullheads.
There is no creak higher then this pond. All the water that gets to it is from watershed that comes across my fields. The pond isn't located in the best place because of this, but I've move hundreds if not a thousand yards of dirt to catch every bit of water that I can to keep the pond full.
We do have herons and egrets there all the time. I didn't see either bring any fish to the pond, but that's how I feel the bullheads got in there. I think it happened last year and my guess is that since it's happened to my small pond, it's happened to my large pond.
Yes, fish will appear in a pond. what fish you get is the question. In my situation, it's not what I wanted, but short of draining the pond and starting over again, I'm stuck with them. Even if I did that, I'm sure it will just happen again anyway.
Eddie
