Mosquitofish, Holbrook's

Gambusia holbrookii

Adult length: 1.5 in (3.81 cm); coloration: light olive-brown color on top, with silvery sides and a yellowish belly. It has rows of black spots on its dorsal (back) fin and caudal (tail) fin. This fish’s mouth is near the top of its head, and it has a black “tear drop” under its eye.








Southeastern United States


Freshwater lakes, ponds, marshes, and slow-moving streams east of the Mississippi River

Life Expectancy

1 to 2 years

Sexual Maturity

Females 6-8 weeks


In the wild, they eat mosquito larvae and pupae, worms, mites, small crustaceans, insects (aquatic and terrestrial), snails, tadpoles, and algae; in the Zoo, they are fed a scientifically developed, commercially available flake and pelleted fish foods and black worms.


IUCN - Not listed


Mosquitofish are very aggressive. They attack and shred the fins of larger fish. They also eat eggs and young of other fish, including largemouth bass and common carp. They sometimes even eat each other. Because they are so aggressive, mosquitofish are almost always in competition with other fish and animals that eat insects. They can “starve out” other fish species and amphibians (frogs, toads, and salamanders). The Holbrook’s mosquitofish breeding season is between mid- spring and mid- autumn with the peak breeding time being around summer. Sexual selection in this species is based on the size of the male. Females tend to choose the larger and more aggressive males. Females also tend to choose areas of shallow water with dark soil cover for brooding sites, while juveniles prefer more rooted plants to hide in. Female mosquitofish are one of our few native live-bearing fish. This means baby fish, known as fry, are born alive; mothers do not lay eggs. It has been shown that females can have up to nine broods per mating season with the average number of fry born ranging from 5 -100. The variability of number of fry born is due to many things including temperature, age, and available nutrients. It has been shown that higher temperatures can increase the reproductivity of this species. The gestation period for this species is between 22 and 25 days. These offspring have a juvenile stage that lasts between 18 days to 8 weeks. Once again, changes in temperature affect these numbers. This means that colder temperatures decrease maturing and higher temperatures can increase maturity. This species can have several generations within their breeding period due to the fast rate of growth.


Special Interests

Other common names include the Eastern mosquitofish. Mosquitofish often have a parasite called “The Big Red Worm.” This worm is actually a nematode, which uses the mosquitofish as part of its life cycle. Other parts of the Big Red Worm’s life cycle involve larger fish, birds, and aquatic worms. This parasite does not usually do much damage to the mosquitofish. Predators of mosquitofish include larger fish, snakes, frogs, turtles, birds, crayfish, and some large aquatic insects.



The Holbrook’s mosquitofish has become an invasive species in Australia, where it was released as a method to decrease mosquito populations. Their ability to thrive in many different environmental conditions which are usually lethal to other fish species makes this a species that is hard to eradicate once established.

Jacksonville Zoo History

Our Holbrook’s mosquitofish were collected on Zoo grounds in 2009. This species has bred here.