Tuesday May 6, 2025
Common names: Western Mosquitofish
Scientific name: Gambusia affinis
Native range: Eastern United States
Status: invasive in much of their nonnative range
Habitat: Freshwater (prefer shallow and slow moving)
Western Mosquitofish (Gambusia affinis) are native to the eastern United States but were introduced to California in 1922 for mosquito control. These fish are small and appear grey/brown with silvery bellies, flattened heads, and rounded caudal fins. This species is sexually dimorphic, and males have thin, streamlined bodies and a long, thin gonopodium, while females are larger and often have distended abdomens with a black gravid spot. Mosquitofish are omnivorous and fecund livebearers that are resilient to changes in water temperature, salinity, and water quality, making them suited for many altered ecosystems that native California fishes can no longer live in. Learn more about their contributions to mosquito control in California in this Fish Report or this Video.
Fun fact: Females can store sperm for several weeks and abort embryos if conditions are not suitable for reproduction!