There is a cetopsis candiru:
http://www.planetcatfish.com/catelog/sp ... ies_id=702

Seems like corydoras eggs would have hatched by now -or- gone white if infertile. And aren't they deposited in little clutches of twos and threes? If they were fish eggs, they would surely have been discovered and eaten by now.

Our channel Catfish all have deeply forked caudal fins. Yeah, but the fork is much less pronounced when they get big. This applies to blues as well. And it is hard to tell much about the tail fork from this picture. I think that the shape of the anal fin is a better distinguishing characteristic ...

Looks like a blue to me as well, but maybe a channel cat. Remember, you said "private pond", so it was probably stocked.

If it is a North American native, perhaps it is one of the madtoms. Search for "madtom" under common names in the cat-elog. I think that all madtoms adapt readily to aquaria, although they may like it a bit cooler with more current than the bullheads. They are a bit smaller, generally maxing out ...