|Scientific Name||Gambusia affinis|
|Other Names||western mosquitofish, plague minnow|
|Size||females about 2.8 in (7 cm), males 1.6 in (4 cm)|
|Age||1 – 1.5 years|
|Habitat||able to adapt to almost any condition|
When used on its own, the term “mosquitofish” usually refers to the “western mosquitofish” (Gambusia affinis). Please note that there is also the “eastern mosquitofish” (Gambusia holbrooki), which is closely related albeit a different species.
The western mosquitofish (Gambusia affinis) are rather small fish, with females reaching approximately 2.8 in (7 cm) and male fish being significantly smaller with 1.6 in (4 cm). They have big eyes and a small mouth. Their coloring is quite dull. The back is an olive green to brown color, the sides and the belly are silver-gray. They are able to adapt their color to both lighter or darker habitats. This is achieved by enriching melanin in cells similar to those which give us humans our tan. Gambusia tend to be aggressive towards other small fish and may feed on their eggs and fry. So you can use them to control the population of bigger species such as goldfish and hinder them from reproducing too much. Mixing them with smaller species should be avoided, as they are a nuisance for other small fish and might even eradicate them completely.
In the wild, their life span usually ranges from 1 to 1.5 years. In an aquarium, it can expand to up to 3 years.
The western mosquitofish stems from the southern states of the U.S. It’s native range spreads down to northern Mexico.
Worldwide mosquitofish have been used in several large-scale attempts to diminish the number of mosquitoes. Mosquitoes are hosts to a number of pathogenic agents. When mosquitoes suck blood from an infected human, they also suck up the germs or viruses within that blood. These agents then can be transferred into the blood cycle of the next individual being bitten. This person then falls ill as well and becomes another source for spreading the disease further.
Among mosquito-borne diseases are malaria, the West Nile virus, dengue, several kinds of encephalitis and yellow fever. In Africa, mosquitoes are the carriers of the horrible disease Malaria. So getting rid of mosquitoes means getting rid of Malaria. These attempts, however, haven’t always been successful. Often the mosquito fish did eat the mosquito larvae but at the expense of other native fish species. In the United States, similar attempts have been made. Here, mosquitoes are usually more of a nuisance than transmitters of dangerous diseases. Mosquito fish have been handed out for free to communities as well as private pond owners. Parts of California still have a program running as of today in order to fight the West Nile virus.
However, again the results are a mixed bag. Most fish feed on insect larvae, when available, so mosquito fish aren’t the only ones diminishing them.
And for them to make an impact in your garden, you probably need to make sure you put them in every pond, lake and other standing water in your area. If your pond is the only one anywhere near, then they definitely will have an impact.
Apart from their promising name, mosquitofish are also a very persevering species. They are able to endure higher acidic levels in the water than most sweet water fish. They are quite immune to a high salinity and can live in brackish water. Plus they can adapt to temperatures anywhere between almost freezing and 95 °F (35 °C).
These qualities helped them to spread quite rapidly beyond the areas where they were introduced by humans to fight against mosquitoes. They can now be found almost everywhere around the globe.
The mosquitofish has been listed as one of the 100 worst invasive species worldwide. So I would only recommend them for your pond when you live in an area, where these fish are native.
How to feed Mosquitofish
They feed mainly on insect larvae, of course. It has been shown that a single female can eat up to 167% of its own weight in larvae in a day. However, some studies showed that mortality rises and the fish get deformations when living solely on mosquitoes. So you might consider feeding them small flake food two to three days a week to give them a more varied diet and keep them healthy.
Apart from larvae they also feed on zooplankton, small insects, tadpoles, detritus as well as other fish species’ eggs and fry. Some studies also showed cannibalistic behavior in times of food shortage. But these studies were under laboratory conditions. It remains unclear whether this kind of behavior also occurs in their natural habitats. Usually, they should be able to find enough other food sources in the wild.
Breeding MosquitofishBreeding season lasts from mid spring until autumn, when the water is at least 57 °F (14 °C) warm. Female mosquitofish don’t lay eggs. Instead the males insert their milt into the female’s genitals via their gonopodium, an anal fin modified specifically for this purpose. This procedure only lasts about a second. After 2,5 to 4 weeks gestation period the mother then gives live birth to approximately 60 baby fish. A female can store a part of the milt of one or several males inside its genitals. Thus it is able to give birth to more broods without being fertilized again. Depending on the temperature, a female can give birth to anything from two up to six broods in one season.
The newborns are about 0.31 in (8 mm) long and can grow at 0.05 in (14 mm) per week. After three to four weeks the females reach sexual maturity and can start reproduction themselves. Male mosquitofish take longer to mature, usually 1,5 to 2 months.