Shorefishes of the Greater Caribbean online information system

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Species: Gambusia affinis, Mosquitofish, Western Mosquitofish

All Families:   All Genera:   All Species:

dark scale edges - > cross-hatching
D 7-8 (5-10)
A 8-11
gill rakers 5-12
male: pectoral 5th ray scalloped, sex organ - no palp, + hooks above tip
lateral scales 26-34

Gambusia affinis (Baird & Girard, 1853)

Western Mosquitofish, Mosquitofish

Head and body moderately robust, moderately compressed at rear; head depressed; front nostril not tubular; covering of eye not continuous with skin of head; mouth small, opens at front, slightly oblique, lower jaw slightly projecting, top jaw protractile; jaw teeth consist of an outer row of large backward curved teeth, and several rows of small pointed teeth; 5-12 gill rakers; 1 dorsal fin with short base, at rear of body, 5-10 (mean 7-8) rays; anal fin origin distinctly before dorsal fin origin in both sexes, female with 8-11 rays; pelvic origin well behind pectoral base, near anal fin, tips of fins of males not swollen; pectorals high on flank, 12-14, modified in male, with 5th ray scalloped near its tip; 3rd anal ray unbranched; anal fin modified in male to form an elongate sex organ, tip of that organ curved upwards, with forward-ward pointing hooks near top of tip, without a fleshy palp; tail base relatively narrow; tail fin rounded; scales smooth and relatively large; 26-34 in lateral series.

Light olive to silvery to yellowish above, pale below; often a dark bar under eye; scale edges dusky, forming a diamond pattern; dorsal fin with 2-3 transverse rows of fine black spots; body may have scattered small indistinct dark spots; gravid female with a dark spot on rear of belly.

Reaches 10 cm.

Freshwater to hypersaline water (0-41 ppt).

Depth range: 0-2 m.

Originally from Delaware to the W Gulf of Mexico, but now worldwide due to introductions.

Note: Often considered to be two separate species: G. affinis (western mosquitofish) with a natural range from about Pensacola (W Florida) to the Rio Panuco in NE Mexico and G. holbrooki (eastern mosquitofish) with a natural range from to about Talahassee eastwards throughout the rest of Florida to Delaware. The two differ slightly in fin ray counts (G. affinis has 1 less anal and dorsal ray than G. holbrooki), in the details of the structure of the male gonopodium and in their genetic characteristics. Here we follow ITIS and the Catalog of Fishes and regard them as one species.

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  • Brackish
  • Freshwater
  • Hypersaline
  • Non Marine
  • Inshore
  • Inshore Only
Water Column Position
  • Bottom
  • Soft bottom (mud/sand/gravel/beach/estuary/mangrove/seagrass)
  • Estuary
  • Freshwater
FishBase Habitat
  • Demersal
Feeding Group
  • Carnivore
  • Data
  • Detritivore
  • Planktivore
  • Data
  • Zooplankton
  • Bony fishes
  • Detritus
  • Insects
  • Mobile benthic worms
Egg Type
  • Data
  • Live birth
  • No pelagic larva
  • No pelagic phase
Global Endemism
  • All species
  • Greater Caribbean non-endemic
  • West Atlantic Endemic
Regional Endemism
  • Continent
  • Continent only
  • Extends North of GC
  • GC non-endemic
  • All species
  • Resident
Climate Zone
  • Subtropical (23-35N, Florida / Carolinas / Bermuda)
  • Temperate (>35N)
IUCN Red List
  • Least concern
  • Listed
  • Not listed
Length Max
  • 10
Depth Range Min
  • 0
Depth Range Max
  • 2