You might think that as thuggy looking as catfish are, plus the whole thing that happens if they stick one of their fins into your hand, they would be apex predators in a small pond. And further, you might think that in a catfish versus goldfish battle for territory, the goldfish would quickly be beaten, finned, and eaten into extinction.
I know I did, but in this case I was wrong. The goldfish are obviously expanding - there are so many of them that it can't be a good sign, and I haven't seen a catfish in a while - also not such a good sign.