Jexnell
is right. Same fish in different color forms. And don't let anyone fool you, the gold form was an expensive and rare fish many years ago, but not anymore.
Early on, early 1970s when rivulatus first arrived in the US (white fins first, then gold), there was confusion on all of this, including which fish was actually
rivulatus. Some, including Alf Stalsberg (who was a hobbyist/collector, not a scientist, a fact some people don't seem to understand about him), insisted that what is now stalsbergi was rivulatus. In fact I had a book years ago with a photo of what is now stalsbergi stating it was the 'true' rivulatus. Some wondered if white finned rivulatus, gold finned rivulatus, and stalsbergi were three different fish. All of this turned out to be wrong and rivulatus, both white and gold fins were confirmed by scientists as rivulatus and
stalsbergi was the 'odd man out' as a different fish.
The whole "saum" thing (white saum, gold saum, silbersaum), when used as though there's something authoritative about it, is comical, really, in that it's basically a hobbyist contrivance with absolutely nothing official or scientific to it. It simply means "hem" or edge in German, referring to fin color.