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The Mosquito Assassin

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Hate mosquitoes? Of course you do! And yet, you love your pond which can turn into a mosquito nursery. Luckily there is a fish ideally suited to keeping your pond free from the little bastards. The western mosquitofish (AKA Gambusia affinis) loves mosquito larvae. Introduce a few of these mosquito assassins into your pond and you’ll keep it mosquito free.

The mosquitofish is a small guppy-like fish that’s sort of a dull grey color.  The females can reach 7 cm and the males 4cm.  Here’s a picture of one:


Don’t be fooled by their unassuming appearance.   They’re tough little guys, able to stand temperatures from almost freezing up to 108 degrees F and live in water with low oxygen saturation and even salinity up to double that of sea water.  They’re super-effective mosquito killers, too.  Just one can easily eat over 100 mosquito larvae per day.  In fact, they’re credited with helping to eradicate malaria in South America, the Ukraine, and South Russia.  The Russians love them so much, they built a mosquitofish monument near the Black Sea:


They’re so tough, they’ve become a problem in Australia.  They were introduced to help control the mosquitoes there and ended up also causing the deaths of some of the local fish and even frogs.  For instance, they’re responsible with the extinction of the rainbowfish around Brisbane.

They’re big time breeders, too.  The females are ready to breed at about 7 weeks old and can have 3 or 4 broods per season.  They’re live bearing, so the survival rate of their young is much higher than most egg laying fish.  Add that to the fact that they can give birth to 60-100 babies at a time and you can understand how they can quickly have a major impact on an ecosystem.  This, combined with the fact that they’ve been introduced to so many environments to help control mosquitoes means that they may now be the most widespread freshwater fish in the world.

Ok, they’re pretty tough, but in order to introduce some mosquitofish into your pond, certain considerations must be made to ensure their health and safety. If you use copper pipes or fittings in your pond where the plumbing actually comes into contact with the water, the pipes must be coated with a special paint to prevent unintentional poisoning. Also, even though mosquitofish can withstand pH levels that are toxic to many other fish species, keeping your pond pH level between 6.5 to 8.0 is important to keep your fish happy.

Certain types of algae and other free floating plant life such as duckweed should be kept to a minimum. Filamentous algae, in small doses, is beneficial to your pond and to your mosquitofish, however care should be taken to prevent the algae from becoming excessive as this will prevent your fish from being able to access the mosquito larvae. These plants should be manually removed instead of chemically controlled to prevent poisoning your fish.

Mosquitofish prefer warm (77-86 degrees F), slow moving water with few floating plants. They actually enjoy living among the roots of water plants, instead. Mosquitofish are omnivorous and will eat a wide variety of prey and detritus, making them a great addition to water gardens that house other fish species. Mosquitofish thrive in ponds that receive several hours of direct sunlight and will languish in heavily shaded ponds.

Natural predators of the mosquitofish include many of the same predators that threaten other pond fish species. These include raccoons, possums, cats, herons, egrets, frogs, and larger predatory fish. Providing plenty of rooted plants and large rocks will give the mosquitofish plenty of places to hide from predators. This is especially important for mosquitofish fry, who must hide from the usual predators as well as adult mosquitofish.

So if you are annoyed by the constant “bzzzzzzz….slap!” of mosquitoes, maybe this little fish is just what you need to take back control of your yard.

Do any of you have any experience with these fish?  Please post your experiences or questions in the comments.


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