Actually, cdawson, the only molly that is supposed to be around here is P. latipinna. The other mollies are Mexican and Central American. I can't tell by looking at the ones I collected that there is any degree of hybridization, they have a perfect P. latipinna coloring, but the males just have little dorsals. I suppose other molly varieties could have been introduced, but our winter water temp hits 50 or less for several months, I doubt any molly other than latipinna could handle that.
newaridiar--- Sailfins do develop (or at least do elsewhere than my creek!) the big male dorsals. In fact, they get bigger dorsals in the wild than in tank-bred specimens. You should see, in person, a full-grown natural male sailfin, quite a showoff! Sometimes you even run across a black-marbled molly in the wild. I just don't know if the ones I collected were too young, or if the swift creek flow is the culprit.