Dave,

I think you probably nailed the source of the fish also...pet store. Someone bought some of these and got tired of them and probably thought they would do the "humane" thing and throw them in a ditch.

There was an article in the Houston Chronicle several months ago about all the amazing fish varieties you can find in Houston drainage ditches aka bayous. Some of the species are very bad, indeed...most all come from the pet stores who sell them to people who grow tired of them and "release" them.

Kind of like all the dogs and cats that are "released" in the country to starve and otherwise terrorize native wildlife species. It's a never ending problem.