Gambusia Identification Guide
Learn to identify Gambusia mosquitofish by their drab olive body, rounded belly, and upturned mouth.
Read the full Gambusia encyclopedia entry →
Key identification features
- Small, drab olive-gray to tan body with little ornamentation
- Rounded, distended belly, especially pronounced in pregnant females
- Small, upturned mouth positioned for surface feeding
- Rounded caudal fin and a small dorsal fin set noticeably far back on the body
- Sometimes a faint dark blotch just behind the eye; females much larger than males, reaching 6-7 cm
Common look-alikes
- Guppies: males show bright, varied coloration and elaborate tail shapes that Gambusia entirely lacks.
- Dwarf livebearer (least killifish): much smaller and shows a distinct blotchy dark stripe along the body, unlike Gambusia's plain flanks.
- Juvenile mollies: rounder-finned and typically show a more compressed body shape than the slender-bodied Gambusia.
Where you'll see one
Gambusia are native to still and slow-moving freshwater habitats such as ponds, ditches, and marshes of the Mississippi basin and Gulf coast, and have been introduced worldwide, where they now thrive in similar quiet, vegetated waters. They are frequently seen skimming near the surface in dense schools, feeding on insect larvae along the shoreline and among floating plants.
Frequently asked questions
How do I recognize Gambusia in a pond or ditch?
Look for a small, plain olive-gray fish with a rounded belly, an upturned mouth, and a dorsal fin set unusually far back toward the tail.
How do I tell Gambusia from a guppy?
Gambusia males stay drab and unadorned, while male guppies display bright colors and elaborate, often flowing tail fins.
Gambusia identified by the community
Recent Gambusia catches identified with Fish Identifier.
