There is a sticky in this forum that lists many species under 8 inches, most of which are correct, or use www.planetcatfish.com
As for the ''hi-fin spotted'' its kind of hard to tell you what size that will hit as it could be any one of a number of different species. My guess is that it will be P. gibbiceps as it's from a chain store, and if so it's certainly not a small fish, expect at least 18 inches.