Western Mosquitofish
Gambusia affinis
Western Mosquitofish is a small livebearing freshwater minnow widely introduced around the world for mosquito control. It is hardy, aggressive, and often abundant in warm shallow waters where it can outcompete native fishes.
Identification points
- Tiny, slender body with a slightly upturned, surface-feeding mouth
- Male with narrow gonopodium instead of a normal anal fin
- Female larger and deeper-bodied, often showing a dark gravid spot near the vent
Habitat
Warm, shallow, still or slow-moving freshwater such as ponds, ditches, marshes, irrigation canals, and vegetated margins of lakes and streams; tolerant of low oxygen and degraded water.
Bait notes
Usually not targeted by anglers; tiny pieces of worm, insect larvae, or micro jigs/micro flies may catch them when needed for bait or study. Their small size makes them poor sportfish.
Behavior
Feeds near the surface and among vegetation on mosquito larvae, small insects, zooplankton, and tiny invertebrates. Males can be persistent nippers and the species often forms loose schools in shallow cover.
Caution
Can be invasive and is regulated or prohibited from release or transport in some areas; do not move them between waters. Handle carefully in warm, stagnant water where water-quality issues may be present.
Fishing notes
Use ultra-light tackle, fine line, and very small hooks in shallow warm water near weeds or the surface. A slow dead-drift or tiny slow retrieve works best; many are captured with dip nets rather than hook and line.