I also have caught them on a variety of flies...mostly nymph or leech patterns, or woolly bugger/ woolly worm patterns.
This "Jumpin' Catfish Nymph" seems to work:
http://freestateflyfishers.org/jumpin-catfish-nymph/


Evenings right at dusk seems to be about the best time. I've caught 'em on bass poppers at night as well.