Western Mosquitofish

Habitat

• Freshwater ponds, rivers, streams and lakes, brackish lagoons
• Also found in rice fields, floodplains and swamps, where they have been introduced for controlling the mosquito population

Description

• A small, stout freshwater fish with a dull grey to brown colour
• A rounded dorsal fin with 7-9 fin rays and small black spots
• An anal fin with 9-10 rays, pale amber in colour
• Mature females are larger than males growing up to 7cm and 4cm in length, respectively
• Females bear live young, producing 3-4 broods in a lifetime, with each brood containing 40-100 offspring
• It feeds on algae, small invertebrates, fish eggs but more famously, mosquito larvae
• Utilised for their presumed value in mosquito-control programmes

Origin and Worldwide Distribution

• G. affinis is native to the freshwaters of eastern and southern USA.
• Widely introduced around the world as a mosquito-control agent, it may be the most widespread freshwater fish

Potential or Known Impacts

• Attacks native fish species, damaging and sometimes killing them, leading to native fish population declines
• Consumes the eggs of commercially important fish species
• Selective predation can alter zooplankton, insect and crustacean communities
• Potential to transmit parasites to native fish species

Is it found in Northern Ireland?

                                                                                                                                                                      How could it get here?

• Historically, spread through mosquito-control programmes but their use as ornamental fish could lead to introductions through accidental or intentional release, both of which are likely reasons for illegal introduction today

Management/Methods for Prevention

• Prevention via enforcing the IAS (Enforcement and Permitting) Order (Northern Ireland) ensuring that G. affinis is not introduced to Northern Ireland
• Reporting all sightings so that Rapid Response can be instigated
• If Rapid Response is not successful, management can include chemical control

Current Legislative Position (Listed on 02 August 2022)

• This species must not intentionally be brought into the Union; kept; bred; transported to, from or within the United Kingdom, unless for the transportation to facilities in the context of eradication; placed on the market; used or exchanged; permitted to reproduce, grown or cultivated; or released into the environment.

Species Related Files:

RA_Gambusia_affinis_Eastern_mosquitofish