I don't know any coldwater catfish that you could buy for an aquarium, but assuming that your going to use it as an algae eater, you could use a Borneo Sucker, they get about 2-4". They're scientific name isGastromyzon, or Beaufortia. But DO NOT keep them with goldfish.
You can buy cold water fish from your local pet store, or aquatic center.
Most other coldwater fish. There are some species of catfish and then there is the Golden Orf and Blue Dace. Check around the local pet shops for coldwater fish. You never know what may be available.
you can use bluegill or you can go to a store and buy catfish bait
Bullheads are not sold commercially, but are common catfish across North America.
What you need to look for is not particularly "freshwater" fish. What you need is Coldwater fish rather than Tropical fish. The coldwater species that may be available apart from all the different types of Goldfish. are Golden Orf, Rudd, Roach, and various catfish species too.
None. Goldfish are coldwater fish. (Keep below 70F). All the sucking catfish that I know of are warm water (tropical) species. (Keep above 70F).
The address of the Coldwater Public Library is: 305 W. Main St., Coldwater, 45828 1604
The address of the Coldwater-Wilmore Regional Library is: 221 E.Main, Coldwater, 67029 0606
Rudd, Golden Orfe, Blue Dace, some species of Catfish. Check with your local pet shop what coldwater species they can get.
teamcatfish.com
There are several species of coldwater fish but no coldwater fish are really suitable for keeping in aquaria IMO because they all belong outside in ponds. There are Blue Dace, Golden Orf, and Koi Carp and several species of catfish to name a few.
A Foot in Coldwater was created in 1970.