Mosquitofish and Allies, Livebearers of the Genus Gambusia
On the surface (and above the waterline), mosquitofish closely resemble Guppies, both being small livebearers with the same basic body plan. Don’t let that fool you though. While Guppies can be territorial, they are more on the placid side of the aggression spectrum while mosquitofish can be extremely nasty to other smaller fish. They may also pick at larger, easygoing fish and as such are best kept in their own tanks. Though more often used for laboratory experiments than fishkeeping, Mosquitofish are hardy animals that take readily to tank life.
Species
Gambusia is one of the 41 Genera under the family Poeciliidae (Livebearing Toothcarp), along with Poecilia (Mollies), Xiphophorus (Platies and Swordtails), and Heterandria (Dwarf Mosquitofish). Gambusia includes 43 species, of which 10 species are native to the United States:
- Gambusia affinis (Western Mosquitofish)
- Gambusia clarkhubbsi (San Felipe Gambusia)
- Gambusia gaigei (Big Bend Gambusia)
- Gambusia geiseri (Largespring Gambusia)
- Gambusia heterochir (Clear Creek Gambusia)
- Gambusia holbrooki (Eastern Mosquitofish)
[pictured]
- Gambusia nobilis (Pecos Gambusia)
- Gambusia rhizophorae (Mangrove Gambusia)
- Gambusia senilis (Blotched Gambusia)
- Gambusia speciosa (Tex-Mex Gambusia)
None of these species are widely sold as aquarium fish, though sometimes mosquitofish are accidentally sold in batches of feeder Guppies. The Western and Eastern Mosquitofishes can be purchased through laboratory fish specimens or through pond supply chains. In the wild, these two are the species you are most likely to encounter (depending on range).
Conservation Status
The Blotched Gambusia is considered Near Threatened by the IUCN. The San Felipe, Clear Creek, and Big Bend Gambusia are Vulnerable, the Pecos Gambusia is Endangered, and the Tex-Mex Gambusia is considered Data Deficient. The other species of mosquitofish are Least Concern or have not been evaluated.
Two species of mosquitofish, the Amistad Gambusia (G. amistadensis) and the San Marcos Gambusia (G. georgei) have been declared extinct.
Distribution
The Mangrove Gambusia is found in southeastern Florida and extends into Cuba. The Western Mosquitofish is distributed across the eastern half of the United States, and the Eastern Mosquitofish can be found along the east coast of the US, from New Jersey and southward.
All other species of Mosquitofish are found in Texas and in Mexico.
Description
Mosquitofish are typically small fish, with both the Eastern and Western
species topping out at about 1.5 inches for males and 2.5 inches for
females. The other species of mosquitofish are smaller, with females reaching less than 2 inches and the males a bit less than that. They all are fairly non-descript in coloration and appearance, but G. holbrooki has a very lovely marbled form found specifically in Florida. Beautiful fish for sure.
Like most livebearers (discounting the similarly named Dwarf
Mosquitofish of the genus Heterandria), mosquitofish males are typically
aggressive to each other and spend most of their time courting females.
In order to prevent over-amorous males from pestering females, a ratio
of 1 male to 2 or 3 females works best. Anecdotal evidence suggests that Mosquitofish are much more
aggressive than other livebearers, though, and will attack other
livebearer males (like Guppies) or harass dissimilar
fish. The best companions for mosquitofish are either small fish that
keep out of the way (like gobies) or other pushy fish such as Florida Flagfish and splitfins like Ameca splendens.
My personal experience is that Mosquitofish (at least G. holbrooki) are normally placid given ample room (mine do great in a 55 gallon with multiple families of fishes) and multiple females per single male. Whether this has to do with the specific species, the tank size, the decor, or being mixed with fish that can “push back” like Banded Killifish is unknown by me - I just lean towards them not being as aggressive as they have a reputation for.
Mosquitofish are outgoing fish, and though likely appreciate rockwork, driftwood, and plants to break up line of sight between fighting individuals, they do not typically hide. They spend most of their time in the top level of the aquarium where they look for floating insect larvae to eat (as implied by their name).
Feeding
Mosquitofish are not typically picky when it comes to food. They prefer live insects and larvae but also take readily to frozen food like brine shrimp, mysis shrimp, and bloodworms. Flake and pelleted foods are also accepted. Like most livebearers, mosquitofish will consume small amounts of algae by picking at plants in the tank.
Take care to feed only in moderate amounts. Adult mosquitofish will eagerly eat up to (or over!) their own weight in food if given the chance.
Water Quality
Certainly not picky about water, provided it is hard (dH 10+) and alkaline (pH 7+). They can survive in water with high turnover and dissolved oxygen levels or stagnant ponds with lower oxygen levels. As long as the water is clean (0 ammonia and nitrites, under 40 ppm nitrates) then there isn’t an issue. This doesn’t mean they don’t need filters, though as small fish that aren’t particularly messy they do not need overpowered ones. Turnover of about 5 times the tank volume per hour is sufficient.
Mosquitofish are adaptable when it comes to temperature. They can survive for a reasonable length of time between 50 and 90 F, though subtropical temperatures around 64 to 68 F are fine. Highest growth rates for juveniles were noted between 75 to 86 F, but this also comes with increased metabolism and aggression.
Brackish Suitability
Mosquitofish are truly euryhaline, with some species tolerating salt levels twice that of the ocean (up to 1.050) for periods of time. It’s unknown whether all species can adapt to fully marine conditions, though all likely tolerate at least low end brackish conditions (up to 1.005) indefinitely. Unless you have soft water, though, there’s not much reason to keep them in brackish water and marine salt can be left out entirely without bothering mosquitofish.
Tank Size
A solitary mosquitofish could be kept in an 8-10 gallon tank without problems, and indeed this is likely best for laboratory conditions. For groups of mosquitofish, 20 gallons (particularly a “long” tank) is a reasonable starting size, though with non-mosquitofish tankmates you’ll likely want to start at 30 or 40 gallons. They can also be kept in ponds, provided the water does not freeze in the Winter.
That said, I observed a large group of mosquitofish cohabitating with Black Mollies and young (1-4 inch) Mayan Cichlids in a small pond with no noted aggression at all.
Breeding
Breeding mosquitofish is extremely easy for the beginner aquarist, and is as simple as putting males and females together and feeding them high quality foods. Females can give birth every 3-4 weeks or so, depending on species, when kept with males. Even when separated from males, the females can store sperm for months and still reproduce. Only females which have never been kept with males (not typically an option for wild caught or store purchased fish) won’t produce fry. Fry can be raised in a separate tank (of at least 10 gallons) and will accept powdered food or finely crushed flake food from day one.
Final Thoughts
Mosquitofish, though hardy and very easy to care for, may not be the best choices for keeping at home. Their aggression and lack of color make it hard to recommend them over other fish. That said, they are abundant in their native range and are very easy to care for. My recommendation is to keep them in large tanks, don’t crowd them, and aim for more (or only) females.
Sources
Fish Identification, Fishbase
Rajkumar, R (1987). “Trophic microvilli of the belated embryos of Gambusia affinis (Baird and Girard) (Atheriniformes: Poeciliidae)”. Journal of the Inland Fisheries Society of India Barrackpore 19 (1): 32–36.
Wurtsbaugh, Wayne A.; Cech, Joseph J. (1983). “Growth and activity of juvenile mosquitofish: temperature and ratio effects”. Transactions of the American Fisheries Society 112 (5): 653–660.
Whiteside, Bobby; Bonner, Timothy; Thomas, Chad; Whiteside, Carolyn. “Gambusia affinis western mosquitofish”. Texas State University.
FAQs on the Gambusia, Heterandria spp. Mosquitofish, Wetwebmedia
Gambusia affinis (Western Mosquitofish), Seriously Fish
issg Database: Ecology of Gambusia affinis, Global Invasive Species Database
Ecology of Gambusia affinis, issg Database
Western Mosquitofish (Gambusia affinis), USGS
(Image Source: Me!)
