The question that came to mind when I saw the pictures is "Are all the high-finned specimens featured really from Purus, Brazil? Or is it because they have high fins and then they were labelled to be from Purus?" In any case, they are fantastic-looking specimens!
Finnage extension amongst well-conditioned, adult males of some species seems to be rather frequently seen. This is also true for some Scleromystax spp. e.g.
S. barbatus, S. kronei, S. macropterus, C113.
Regards,
Alan