Sailfin
A variant of Molly (Poecilia sphenops)

Representative Mollyphoto — a dedicated image of this exact morph isn't available yet.
Tall, banner-like dorsal fin (most dramatic in males) inherited from Poecilia latipinna/velifera lines.
Keeper tips for this variant
Needs a larger, longer tank (75 L+) and pristine water to grow the dorsal fully; warmth (26-28°C) helps fin development.