Shortfin Molly Identification Guide

Key identification features

• Stocky, moderately compressed body with an olive-gray to silvery ground color
• Short, rounded dorsal fin (roughly 6-9 rays), never sail-like
• Rows of small dark spots along the sides that often merge into faint horizontal lines
• Rounded caudal fin without extensions
• Males show a gonopodium (modified anal fin) and reach smaller sizes than females, which can approach 10 cm

Common look-alikes

• Sailfin molly (Poecilia latipinna): easily separated by its tall, sail-like dorsal fin with many more rays; shortfin molly's dorsal stays low and rounded.
• Common molly (Poecilia sphenops): nearly identical in shape and color; best distinguished by native range and fine differences in dorsal-fin ray counts rather than obvious field marks.
• Amazon molly (Poecilia formosa): a naturally occurring hybrid with intermediate, often plainer patterning and no distinct male form since it reproduces asexually.

Where you'll see one

Shortfin mollies inhabit fresh to brackish waters along the Gulf slope from Mexico south into Central America, including slow streams, spring-fed pools, and coastal lagoons, often in large mixed schools near vegetation.