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Robyn's Mosquito Fish Page

Last Updated: 11/12/13

Quick Information
Description, Varieties, Detrimental Effects of Mosquito Fish, and a Trap
Setup and Water Preferences
Sexing
Breeding
Prolificness and My Fish
Where Can I Get Some?
Links and Pictures

Are mosquito fish good or bad? You decide from the facts presented.

For information on mosquitoes and controlling mosquitoes, go to my Mosquito Page.

For controlling mosquitoes using fish, I recommend fathead minnows instead of mosquito fish. They are more hardy, less nasty, and do a better job of eating mosquito larvae. Go to this page for more information than you need on them.

Quick Information

Common name: Mosquito fish, mosquitofish
Scientific/Latin name: Gambusia affinis (other species are also called mosquito fish)
Maximum length: Males 0.5 to 2 inches, females 1 to 3 inches
Colors: Natural brownish gray
Temperature preference: 60 to 80 degrees F, can survive 33 to 100 degrees F
pH preference: 7 to 8
Hardness preference: Moderate to hard
Salinity preference: 1 Tablespoon per 5 to 15 gallons
Compatibility: Not recommended for community tanks or ponds with other fish present, especially if you wish to have fry of other species survive
Life span: 1 to 3 years
Ease of keeping: Easy
Ease of breeding: Super easy

Description, Varieties, and Detrimental Effects of Mosquito Fish

There are many species called mosquito fish. They may more properly be called mosquitofish but, English-wise, making it two words makes more sense to me. So, I may be writing it the wrong way. All mosquito fish are livebearers. I am referring specifically to Gambusia affinis. There are a number of subspecies. Other Gambusia species include G. holbrooki from the East Coast of the US; G. amistadensis, G. gaigei, G. geiseri, G. georgei, G. heterochir, and G. senilis from Texas; G. noblis from Texas and New Mexico; and G. rhizophorae from Florida and Cuba.
G. affinis and similar species are insignificant in color, a melange of brown, dull yellow, and black. Females grow up to 3.25 inches while males grow up to 1.75 inches depending on the subspecies. Usually the fish stay around an inch long. Mosquito fish are far from perfectly peaceful. Mine used to harass each other and other fish. In a pond setting, they are less bullying. They also will eat some of their babies. Each fish should have a few gallons to itself but can thrive in high densities with more than five fish per gallon. They will live at least a few years. Mosquito fish are native or introduced to much of the United States. Here in Maryland, they inhabit many drainage ponds and ditches. They are used for mosquito control in stagnant water. Mosquito fish are normally naturally colored but there are hard-to-find orange/yellow and albino variants out there.

A large female can eat 100-200+ mosquito larvae in a day! More often mosquito fish will eat other tasty insect larvae and fish fry. One scientist examined the stomachs of over 2000 mosquito fish and found only a small percentage of mosquito larvae. Instead, aquatic insects and fry made up most of their diet. For this reason, they are best used in small ponds where fry of other species are not desired. I keep mine in tub ponds too small for other fish. There is debate over how efficient mosquito fish are at mosquito control. Generally, mosquito fish will not drastically reduce mosquito larvae populations in large bodies of water. Instead, they will eat other insects and fry preferentially. This can have a detrimental affect on insect and native fish populations. For this reason, mosquito fish should not be introduced into natural waters in which they are not native. In personal ponds, they usually will eat most small insect larvae present, including mosquito larvae.

A new study in late 1999 indicates that mosquito fish may be a major part of the decline of small frogs and newts in California. Apparently, mosquito fish prefer to eat Pacific treefrog tadpoles more than mosquito larvae. So, be aware that mosquito fish may also eat small amphibian larvae including those of frogs, toads, salamanders, and newts. This is yet another reason to keep these fish out of natural waters. My mosquito fish did not appear to reduce the number of green frog tadpoles in their pond most likely because these frogs and their tadpoles are relatively large and the adults laid many eggs.

A new thread on rec.ponds has people renaming the mosquito fish "dambusia" instead of gambusia due to their tenacity against other fish and animals. Many ponders are finding that they reproduce too quickly and eat any other small fish. This may not occur with everyone though. All my mosquito fish died after two winters. Anyway, for those of you wishing to trap and remove "dambusia" from your pond, here is the recipe that Dwight has for a trap. Cut off the top of a 2 L soda bottle (with no cap on) about 1/3 of the way down and flip the top over so it sticks into the bottom. Drill a few holes in the base of the bottle to let water in, and tie a string to the base so you can pull the trap in. Put food (fish food, meat, bread) in through the top. Put this in the pond where it should float. Fish can swim in through the bottle neck but have trouble finding the way back out.

NEVER release mosquito fish into the wild! Even if they are native to the area, adding more will increase the stress on local fish and amphibian populations.

Setup and Water Preferences

They can take a range of pH's from about 6.0 to 8.5. They also can take a variety of hardnesses. As with most livebearers, a moderate hardness and some added salt can be beneficial. Mosquito fish are known for their ability to survive in almost any collection of water outside. They can survive temperatures from the high 30's to the high 90's degrees F but between 60 and 75 degrees F is best if it can be controlled. Provide plants and other hiding places. They will eat flake food and some algae but prefer live insect larvae and fry. They also eat mosquito larvae, hence their name. Frozen bloodworms, tubifex, and mosquito larvae are all eaten with relish.

Sexing

They are easy to sex. Besides the mature female being significantly larger and fatter, the mature male has a gonopodium. This tube-shaped fin acts like a penis does in mammals. The female also has a black patch near her vent where fry develop. She will greatly increase in size as the fry develop.

Breeding

If you put at least one mature male and one mature female together in at least five gallons of water, and the temperature is between 65 and 80 degrees F, you will most likely be expecting fry soon. A female can retain sperm from a single mating to create several batches of fry. Some books suggest placing more males than females together, unlike with other livebearers. After about 24 days, the females will give live birth to 10-100 babies. Newborns are a large 3/8 of an inch. In small tanks, the female should be placed in a net or birth box for livebearers when it looks like she is ready to pop. The fry should be visible as a black spot near her vent. After the babies are born, remove the mother from the box. She will eat her young as will most fish that see them. Nonetheless, because the fry are so large for fry, a large percentage of the fry elude predation in a pond.

In a pond, these fish usually breed virtually out of control and soon, with no help from you, there should be hundreds of fry. This may seem like too many for your pond but many may die over winter in areas with freezing temperatures. Excess fish or unwanted fish can be trapped using the trap described above. The fry are rather large and can take finely crushed flakes, prepared baby foods, and newborn brine shrimp right away. In ponds, they will find food on their own. Keep the fry at around 75 degrees F. In July, 1998, the 6 adult mosquito fish that I put in an outdoor tub in Spring 1998 with plants and only about 10 gallons of water had turned into 104 fish of all sizes. They loved eating frozen white mosquito larvae that I fed them.

More information on fry care can be found at my breeding and fry care page but this information is really geared towards egg-laying fish.

Prolificness and My Fish

Information on the ponds that I have had and do have mosquito fish in can be found on my former 50 gallon pond page and my 50 gallon lotus tub and 153 liner pond page.

To less than 5 gallons of water, one pair of mosquito fish were added in the Spring of 1998. On 10/11/98, 14 fish were removed. At least three full sized, pregnant females were included.

To less than 10 gallons of water, 6 adult mosquito fish were added in the Spring of 1998. Five small fish were removed during the summer to another pond (the 16.5 gallon). By 10/24/98, 91 were removed to be overwintered in a heated 50 gallon pond. They ranged from newborns to huge females. Most were medium sized. Wow, that is a lot of fish!! Another three were never caught. They multiplied into a dozen before the tub pond froze solid, killing them all.

Thus, you can see that mosquito fish can really breed even in tiny puddles of water. They apparently do not have a high propensity to eat their own fry (but they sure love fry of other species).

The 102 or so mosquito fish moved into the 50 gallon rubbermaid pond had dwindled to only a single female and her fry by spring that were moved to the new 50 gallon lotus tub pond while the 153 gallon was being built. The mosquito fish had almost all died, either from the cold, from eating each other, or from some predator like a raccoon. So, even though mosquito fish can breed like crazy, their population can crash to almost nothing during a winter, even with a de-icer keeping the pond completely open!

In the fall of 1999, 17 mosquito fish were retrieved from the 50 gallon lotus tub and moved to the new 153 gallon pond. When I cleaned out the 153 gallon pond on 3/26/00, I did not find a single mosquito fish left. Since I only changed half the water and ran the net all over to collect debris, one or two may have eluded capture but I do not think so. All 17 must have perished. From a high of over 110 mosquito fish, I now have zero. A 100% cleaning out of the 153 gallon pond on 3/26/01 verified that there are no mosquito fish at all left.

Where Can I Get Some?

Mosquito fish are often given away free by local governmental agencies in an attempt to control mosquitoes. Try locating whatever agency is in charge of mosquito control in the area to obtain some. Also, in many areas, they occur naturally in bodies of water, including ditches, ponds, lakes, streams, and anything else containing water for any length of time. I do not know of any restrictions on collecting them from the wild (aside from getting the land owner's permission). Jan Jordan alerted the rec.ponds newsgroup that in Washington state, it is illegal to transport mosquito fish but the state will give you some. There is some confusion as to whether the species in question are native or introduced species that cannot survive the winter. Please e-mail me if you have any info on this law or those of other states.

If you or someone you know works at a school, university, or at a science-related business, Carolina Math and Scientific will send you a catalog there. They will ship to individuals homes, just not send the catalog there. I got my mosquito fish from them. I ordered 12 but got only 8 alive and 2 dead. No matter, in just a few months, their numbers were up to nearly 100 in only two tubs with 10 gallons of soil and 10 gallons of water! Of course, after a few years, they all died. Their number is 1-800-334-5551.

Here are a few places that sell mosquito fish:
Fattigfish
HT Aquatics - also has information
Autumn Koi - also sell albino mosquito fish (they e-mailed me this; I cannot find the mosquito fish on their web site though)
Liveaquaria.com - part of Drs. Foster and Smith, sells mosquito fish.
Live Aquaria deleted their affiliate program so these links will no longer work. I am leaving up the pictures which are still working for now.

Links and Pictures

Mosquito fish - at Lilypons on 9/2/07.

These links were last checked on 3/3/06. Links that did not work were replaced with archived versions, or if none found, deleted.

Mosquito Fish - page with some information on Gambusia affinis as well as nice drawings of a male and a female mosquito fish. This is an archived version of the site as the original is gone.

Mosquito Fish - a short page on Gambusia affinis and a photo of a male mosquito fish. Jim informed me that the photo is not of Gambusia affinis but in fact a male Heterandria formasa or least killifish, native to Florida.

Gambusia Control Homepage - the anti- Gambusia contingent

Adverse Assessents of Gambusia affinis - NANFA article on negative impacts of mosquito fish

Albino Mosquitofish - this page has drawings of mosquito fish and some technical information. This is an archived version of the site as it no longer exists. I am not sure why it says "albino" as the page has no other mention of that. I had not heard of or seen albino mosquito fish but then Lee e-mailed me to say he has raised albino mosquito fish. They are white with pink eyes. This place in California breeds them, and there are photos of some on their site: Contra Costa Mosquito Vector & Control District.

Swedish Livebearer Site. This is an archived version of the site that no longer exists.

Mosquito Fish Information

Jonah's Aquarium - a single photo of a regular mosquito fish, a golden one, and an albino one all together.

Thanks to Gregory for these additional mosquito fish links:

Mosquito Fish - page from the Los Angeles County West Vector & Vector Borne Disease Control District.

Mosquito Fish - from the Illinois-Indiana Sea Grant site.

Mosquito Fish facts - from Exotic Aquatics (pond builders).

Keeping Gambusia affinis

Gambusia - site by New Zealand's Department of Conservation.

For more links on native fish that may include information on mosquito fish, check out my native fish page.


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