You have Metynnis fasciatus, perhaps the rarest SD. I think it's the best looking. Fishbase doesn't have much to say:
http://www.fishbase.org/Summary/speciesSummary.php?ID=56433
Myleus schomburgkii is a close cousin of myloplus rubripinnis, or Red Hook. A writer for Practical Fishkeeping suggests that there should be more than one species here: "There are currently three regional variants of the species. Two to me look very similar, but I suspect that the first will soon be described as a different species. This variant sports blue-white finnage with an extremely broad vertical band while the other two have a red anal fin and a narrower black band. (I keep seeing this quote but I can't find the article. The writer is Richard Hardwick.)
Here's the Emperor Blue Hook. I'm finding aquarists with 13" specimens (they get thick too). These are sometimes sought as Piranha and Pacu substitutes.
I have two of the red hooks, labeled by my LFS simply as Black Belts, $47 each. Note how their single bar is thinner than the Blue Hooks' and their fins have an orange tint. Anecdotal evidence suggests that they don't get as big. That's also wishful thinking on my part.
