The biggest difference is I know where to get spottails. But I don't think there are spotfin in my state.
Does your state have red shiners? They are same genus (Cyprinella) as spotfins and likely will spawn in similar habitats. Literature says they are tolerant of numerous conditions and tolerate suspended silt. Spawning is variable and not quite as specific as most of the other Cyprinella species. Pond spawning should be possible since they reportedly scatter eggs over similar areas as GSH and also in crevices. Sometimes one has to make a road trip to an area known for the species to probably do some self collecting. Sometimes you might be able contact local bait shops where the species occurs and buy some of them from the bait shop.
Some of the distribution maps show red shiners extending up into south central North Dakota. One may have to take a long weekend vacation to a place that sells red shiners as bait fish.
http://ninnescahlife.wichita.edu/node/367
