Thanks, everyone. He's from a small creek in middle Tennessee. This one is male (females are relatively drab), but he's not yet in his full nuptial coloration, which will be even more spectacular.
This individual was about 3" in length, which is typical adult size for his species. Other darters range from less than 1.5" to nearly a foot, and most of them have brightly colored males.
Jaysen- yes, all darters live in freshwater, and they are endemic to the US and Canada (east of the Rockies). Most species live in smaller streams, but there are also big-river and swamp darters. Some of the swamp-dwelling species are common stowaways in feeder shrimp tanks.
*EDIT* Most darters make good aquarium inhabitants, provided you can give them a little current and lots of bloodworms, blackworms, and other live or frozen inverts.