I think Jelly has Melanopterus, Sao Fransisco and Hilarii- the SF variety seem to develop brown fins rather than black and some colour in their fins. The Amazonicus are very similar;
Mela-
Amazonicus-
Images are from google and in fact, through searching, there is also Brycon Falcatus and Cephalus to add to the list of possibly confused with Melanopterus-
Falcatus-
Cephalus-
Ok, so next to each other there are noticable differences but likewise, there are a lot of similarities. And there maybe other species.