Mosquitofish

Gambusia affinis

Common name:

Mosquitofish

Scientific name:

Gambusia affinis

Alternative common names:

Western mosquitofish, gambezi, guayacon mosquito (Spanish). 

The mosquitofish is a species of freshwater fish indigenous to the Mississippi River in the USA. It is listed as one of the world’s worst invasive species. The name 'mosquitofish' was given because the diet of this fish predominantly consists of large amounts of mosquito larvae (as well as other invertebrate larvae); an adult female can consume hundreds in a day.

Additional Info

  • Where does this species come from?

    Eastern and southern United States of America.

    What is its invasive status in South Africa?

    NEMBA Category 1b in national parks, provincial reserves, mountain catchment areas and forestry reserves declared in terms of the Protected Areas Act. NEMBA Category 2 for breeding for the purpose of feeding stock for zoos and animal breeders. NEMBA Category 3 for all other discrete catchment system in which it occurs.

    Where in South Africa is it a problem?

    Sundays River Valley, Eastern Cape.

    How does it spread?

    Mosquitofish can be spread during floods and through unintentional relocation when it is inadvertently transported in aquatic equipment, such as nets, boats and fishing gear.

    Why is it a problem?

    Adults are extremely aggressive and attack other fish, shredding their fins and sometimes killing them. They are known to prey on eggs, larvae and juveniles of various fishes, including largemouth bass and common carp. They are also known to prey on adults of smaller species.

    What does it look like?

    Description: Mosquitofish is a small, live-bearing fish, dull grey or brown, with no bars or bands on the sides, and a rounded tail. The body is short and the head flattened, with the mouth pointed upward for surface feeding. It may have a large dusky to black teardrop marking beneath its eye, but this marking is sometimes reduced. Females have a rounded, small anal fin and grow to about 6-7cm. Males grow to about 4cm. Habitat: It occurs in a variety of freshwater and protected brackish environments. It preferentially occupies vegetated ponds and lakes, backwaters and quiet pools of streams. It is most often encountered in standing or slow-flowing waters. Breeding: Sperm transfer occurs when males insert their gonopodium in the oviductal opening of the female. Females can store viable sperm for several months. After fertilisation, young are born in about 24 days. Maturity occurs after one month for males and six weeks for females. The maximum age of mosquitofish is four years. They prefer temperatures between 12-29 degrees Celsius. However, in deep enough water they are able to reduce activity and go into a hibernation-like state.