Eastern mosquitofish

Habitat

• Can adapt to a variety of aquatic habitats from freshwater to marine, cold temperate waters to tropical but prefers sluggish to fast flowing water
• Principally found to inhabit terrestrial freshwater waterbodies like rivers, lakes, lagoons, and ponds
• Can tolerate near-coastal environments, inhabiting mudflats, salt marshes, the inter-tidal zone, and mangroves
• Found abundantly in the shallow waters of near-shore environments, close to dense vegetation to avoid predation

Description

• Translucent grey in colour, with a blueish sheen on the sides and a silver belly
• Fins are colourless with black spots dotted across them
• Males can have irregular black blotching patterns and are smaller in size to females, 35mm and up to 60mm, respectively
• Often misidentified as the Western mosquitofish but differentiated by differences in the male anal fin
• Can quickly establish a large population due to rapid maturation rates and high survival rates of offspring
• Introduced across the world to control mosquito populations

Origin and Worldwide Distribution

• A native range of the Mississippi Basin and the tributaries to the Northern Gulf of Mexico
• Due to deliberate human introductions, it is now found across the world, present on all 7 continents

Potential or Known Impacts

• Competes with native fish species for habitat, food and spawning areas
• Lacking natural predators, they increase in size and therefore feeding rate, monopolising food resources
• Consumes the natural predators of mosquitos, leading to increase in mosquito populations
• They attack and injure native fish, leaving them susceptible to disease
• Predation on the eggs and juveniles of native fish lead to population declines

Is it found in Northern Ireland?

• It is not currently present in Northern Ireland

How could it get here?

• Initially introduced deliberately to aid in controlling mosquito populations, locally, nationally and globally
• Spread has also been a result of flooding and using the fish as bait
• Illegal introduction is the most likely cause of spread here

Management/Methods for Prevention

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

Research

Species Related Files:

RA_Gambusia_holbrooki_Eastern_mosquitofish