I took scrapings from 3 fish, but didn't see anything that even
closely resembled flukes or any other parasite activity I've read
about. The mucus all looked normal and there wasn't a lot of activity
on the slides.

I did see this thing:
http://homepage.mac.com/pondstuff/PhotoAlbum2.html

I'm not sure what it is. I saw a few of those. Are they just worms?

Also, is there a good source (book or online) for deciphering what I'm
looking at under the microscope? I'd like to learn more about what I'm
seeing.

The injured fish is still swimming around, but has started resting
(right side up) with its fins against the bottom of the pond. It looks
worn out, but it's still eating and still swimming. It's just taking
more breaks.

Dave