Howdy PP,
I just entered this field, thus, I am far away from being a silverdollar expert. However, if I understand it correctly, some varieties of regular silverdollars can simply have a red anal fin. Only the red hook has the hook. My smallest is 3'', and it has a very pronounced hook already. Maybe someone can chime in who bought them a bit younger.
Geez, two things I've learned over the weekend: These guys are skittish as hell. They drive the other fish crazy. I hope they'll calm down in the next few weeks. Second, they eat like cows. I will have to buy the jumbo flake food boxes in the future.
They do not touch Crypts nor Vallisneria nor water lettuce, but they seem to like fresh Echinodorus leaves. As compared to regular silver dollars, who eat every green in the tank. To me, the beautiful looks and the associated minimal reduction of plant-diversity are a compromize well worth it!
HarleyK